^m^:- 


STEAM-BOILEK  ECONOMY 


A  TREATISE  ON  THE  THEORY  AND 
PRACTICE  OF  FUEL  ECONOMY  IN 
THE  OPERATION  OF  STEAM-BOILERS 


BY 


WILLIAM  KENT,  M.E.,  Sc.D. 

AUTHOK  OF  THE   MECHANICAL  ENGINEERS'   POCKET-BOOK 


SECOND  EDITION, REVISED  AND  ENLARGED;  WITH  NEW  CHAPTERS 

ON  BOILER  DESIGN  AND  CONSTRUCTION,  AND  BOILER-ROOM 

APPLIANCES 

TOTAL  ISSUE,   FIVE  THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS,  lire. 

LONDON:  CHAPMAN"  &  HALL,  LIMITED 

1915 


\< 


COPYRIGHT,  1901,  1915 

BY 
WILLIAM  KENT. 


THE  SCIENTIFIC  PRESS 

ROBERT  DRUMMOND  AND  COMPANY 

BROOKLYN.  N.  Y. 


PREFACE   TO  THE   SECOND   EDITION. 


IN  the  fourteen  years  since  the  first  edition  of  this  book  was  issued 
numerous  improvements  have  been  made  in  boiler  practice.  Steam 
pressures  have  increased,  but  methods  of  construction  and  of  caring 
for  boilers  have  improved  to  such  an  extent  that  there  are  fewer  ex- 
plosions relative  to  the  number  of  boilers  in  use.  There  is  more  than 
twice  as  much  coal  burned  per  day  in  the  Western  cities,  but  the  smoke 
nuisance  is  decreasing.  The  increased  fuel  economy  due  to  the 
adoption  of  better  methods  of  burning  coal  has  raised  the  maximum 
boiler  efficiency  obtained  in  the  best  practice  with  soft  coal  from  76 
per  cent  to  81  per  cent,  and  the  efficiency  in  average  practice  has 
probably  increased  in  a  greater  ratio.  Boilers  are  now  driven  in 
electric  power  stations  at  double  their  former  rate,  with  higher  fuel 
economy  and  with  decreased  cost  of  labor  and  maintenance.  The 
possible  saving  of  money  by  the  operation  of  boilers  by  modern,  as 
compared  with  old  methods,  is  so  great  that  it  is  now  recognized  that 
the  boiler  plant,  rather  than  the  engine  room,  is  the  place  where 
money  is  made  or  lost,  and  that  it  pays  to  study  and  to  adopt  modern 
methods  in  the  boiler  plant,  to  keep  statistics  of  operation,  and  to  em- 
ploy intelligent  and  high-priced  labor. 

The  several  elements  that  have  contributed  to  the  improvements 
in  modern  practice  and  the  nature  of  the  results  obtained  from  them 
may  be  tabulated  as  follows : 

IMPROVEMENTS  RESULTS 

Much  larger  boilers Economizing  real  estate  and  cost 

of  setting. 
Very  large  combustion  chambers.      Burning  coal  without  smoke. 

Eapid  driving Economy  in  cost  of  plant. 

Coal-  and  ash-handling  machinery.     Dispensing    with    all    labor    for 

shoveling  and  wheeling  coal. 
iii 


AQAJ. 


iv  PREFACE  TO  THE  SECOND  EDITION. 

Mechanical  stokers Feeding  coal  uniformly,  avoiding 

loss  due  to  opening  of  doors. 
Eegulating  the  coal  and  air 
supply  so  as  to  maintain  uni- 
form furnace  conditions. 

Gas  analysis Check  on  the  air  supply,  enabling 

the  operator  to  adjust  the  air 
supply  to  that  required  for 
maximum  economy. 

Superheaters Insuring  dry  steam  and  improving 

engine  efficiency. 

Draft  gauges Enabling   the   operator   to   know 

at  all  times  the  difference  in 
draft  pressure  between  the  ash 
pit  and  the  furnace  and  between 
tfie  furnace  and  the  flue,  and 
to  equalize  the  draft  in  the 
several  boilers  of  a  plant. 

Electric  pyrometers For  finding  temperatures  at  dif- 
ferent points  in  the  gas  pas- 
sages, to  discover  if  the  baffling 
is  in  good  order. 

Purchase  of  coal  under  specifica-  Enabling  the  purchaser  to  obtain 
tions,  analyses  and  calorimeter  coal  of  known  quality  for  a 
tests  of  coal stated  price. 

Treatment   of  feed-water Diminishing  the  danger  and  the 

loss  of  economy  due  to  scale,  the 
.  cost  of  removal  of  scale,  the 
time  boilers  are  out  of  service 
for  cleaning  and  for  repairs, 
the  cost  of  renewal  of  tubes  and 
other  repairs. 

Better  construction  and  higher  Diminishing  danger  of  explosion, 
factors  of  safety. 

Eecording  and  plotting  of  boiler  Knowledge  of  performance  under 
performance.  different  conditions  of  opera- 

tion. 

Bonus  and  premium  systems  of  Securing  maximum  efficiency  of 
payment  of  wages.  labor. 


PREFACE  TO  THE  SECOND  EDITION.  v 

In  the  present  edition  all  of  these  several  improvements  are  dis- 
cussed at  length.  Numerous  records  of  recent  tests  of  different  kinds 
of  boilers  are  given,  showing  the  efficiency  that  may  be  obtained  with 
different  coals  under  different  conditions  of  operation. 

The  author's  formula,  given  in  Chapter  IX,  showing  the  relation 
that  exists  between  boiler  efficiency,  the  rate  of  driving,  the  air 
supply,  and  other  variables  that  have  a  relation  to  efficiency,  has  been 
developed  so  as  to  show  the  effect  of  imperfect  combustion  and  of 
moisture  in  coal,  and  a  new  straight  line  formula  for  efficiency,  as- 
suming complete  combustion,  and  plotted  diagrams  made  from  it 
has  been  devised,  enabling  the  user  to  predict  the  maximum  economy 
that  can  be  obtained  with  different  rates  of  driving  and  different  pro- 
portions of  air  supply.  New  tables  of  analyses  and  heating  values  of 
American  coals  are  given,  and  the  chapters  on  Coal  Fields  of  the  United 
States  and  Heating  Value  of  Coal  have  been  revised. 

Two  new  chapters  have  been  added,  one  on  Boiler  Design  and  Con- 
struction, and  one  on  Boiler  Attachments  and  Boiler  Room  Appliances, 
which  will  make  the  book  as  a  whole  more  useful  to  students. 

NEW  YORK,  July   1,  1915. 


EXTRACT  FROM  THE  PREFACE  TO  THE  FIRST  EDITION,  1901. 

IN  the  year  1875  the  author  made  his  first  evaporative  test  of  a 
steam-boiler.  It  was  the  Pierce  rotating  boiler,  which  was  tested  at 
the  Centennial  Exhibition  the  following  year.  It  had  certain  peculiar- 
ities of  design  which  were  supposed  by  the  inventor  to  make  it  more 
efficient  than  any  other  boiler  then  on  the  market.  The  testing  of  this 
boiler  and  of  two  others  during  the  same  year  led  the  author  to  study 
seriously  the  problem :  "On  what  conditions  does  the  fuel  economy  of 
a  steam-boiler  depend  ?"  For  three  years,  1882-5,  he  was  in  the  em- 
ploy of  the  Babcock  &  Wilcox  Co.,  and  it  was  part  of  his  work  to  make 
evaporative  tests  of  the  boilers  made  by  that  company,  and  of  other 
kinds  of  boilers  for  comparison,  in  different  sections  of  the  country, 
and  with  all  kinds  of  coal.  In  connection  with  his  office  practice  from 
1890  to  the  present  time,  he  has  had  occasion  to  make  nearly  a  hun- 
dred boiler-tests,  with  different  boilers,  fuels,  and  furnaces.  Besides 
having  this  practical  experience,  together  with  the  habit  of  studying 


vi         EXTRACT  FROM  PREFACE  TO  FIRST  EDITION,  1901. 

critically  the  result  of  each  test  for  the  purpose  of  drawing  conclusions 
from  it,  the  author  has  been  a  constant  student  of  the  literature  of  the 
subjects  of  boiler-testing  and  fuel  economy  which  from  time  to  time 
appears  in  the  transactions  of  engineering  societies,,  in  the  technical 
press,  in  trade  catalogues,,  and  in  books.  He  has  thus  been  enabled  to 
compare  theory  with  practice. 

Many  books  have  been  written  on  the  subjects  of  boilers,  furnaces, 
and  fuels,  but  in  none  of  them  does  it  seem  that  the  problem  of  steam- 
boiler  economy  has  been  treated  with  the  thoroughness  which  its  im- 
portance deserves.  Most  of  the  treatises  on  boilers  devote  the  greater 
part  of  their  space  to  details  of  construction,  and  only  a  small  space 
to  the  subject  of  fuel  economy.  There  appears  to  be  a  demand  for 
a  new  book  which  shall  treat  solely  of  steam-boiler  economy  and  of 
subjects  related  thereto.  To  supply  such  a  demand  this  book  is  offered. 


CONTENTS 


CHAPTER  I. 

PRINCIPLES    AND    DEFINITIONS 

PAGE 

List  of  Subjects  to  be  Studied 1 

Heat 2 

Temperature 2 

Heat-unit 3 

Unit  of  Evaporation 4 

Latent  Heat 4 

Specific  Heat 4 

Quantity  of  Heat 6 

Heat  of  Combustion 7 

How  Smoke  may  be  Burned : 9 

Flame 9 

Transfer  of  Heat 10 

Capacity  of  a  Boiler .  .  . 11 

Boiler  Horse-power 11 

Efficiency  of  a  Boiler 12 

Operation  of  a  Boiler r 12 

Efficiency  of  the  Heating  Surface 14 

CHAPTER  II 

FUEL    AND    COMBUSTION. 

Chemistry  of  Fuel  and  Combustion 17 

Carbon 17 

Hydrogen 17 

Oxygen 18 

Nitrogen 18 

Sulphur 18 

Properties  of  Air 19 

Relative  Humidity 19 

Weights  of  Air,  Vapor  of  Water,  etc «... 20 

Heating  Values  of  Various  Substances 21 

Heat  Absorbed  by  Decomposition 22 

Heating  Value  of  Compound  or  Mixed  Fuels 23 

Available  Heating  Value  of  Hydrogen 23 

Available  Heating  Value  of  a  Fuel  Containing  Hydrogen 25 

vii 


viii  CONTENTS. 

PAGE 

Temperature  of  the  Fire 26 

Maximum  Temperature  due  to  burning  Carbon 27 

"                   "            "    "        "       Hydrogen 28 

Temperature  of  the  Fire,  Fuel  Containing  Hydrogen  and  Water 29 

Excessive  Carbon  Monoxide  Due  to  Heavy  Firing 33 

Calculation  of  Weight  of  Air  Supplied 33 

Air  Supply  Required  for  Different  Grades  of  Coal 36 

Heat  Carried  away  by  the  Chimney  Gases 37 

Errors  in  Analysis  of  Furnace  Gas 38 

Heating  Value  of  Sulphur  in  Coal 39 

Hygrometric  Properties  of  Coal 40 


CHAPTER  III. 

COAL. 

Production  of  Coal  in  the  United  States 42 

Formation  of  Coal 44 

Progressive  Change  from  Wood  to  Graphite 45 

Classification  of  Coal 46 

Caking  and  Non-caking  Coals 50 

Long-flaming  and  Short-flaming  Coals 51 

Cannel  Coals 51 

Lignite  or  Brown  Coal,  Sub-bituminous  Coal 51 

Decrease  of  Weight  of  Lignite  in  Transit 52 

Composition  of  Ash 53 

Proximate  Analyses  and  Heating  Value  of  Coals 54 

Approximate  Heating  Values  of  Coals 56 

New  Classification  and  Tables  of  Heating  Value 58 

Air  Drying  of  Coal 73 

Different  Methods  of  Reporting  Coal  Analyses 73 

Reliability  of  Dulong's  Formula 77 

Nature  of  the  Volatile  Matter  in  Coal 79 

Relation  of  Quality  of  Coal  to  Capacity  and  Economy  of  a  Boiler 80 

Valuing  Coals  by  Test  and  by  Analysis 82 

Selection  of  Coal  for  Steam  Boilers 83 

Specifications  for  Purchase  of  Coal 85 

CHAPTER  IV. 

COAL-FIELDS   OF   THE    UNITED    STATES. 

Maps  of  Coal-fields  of  the  United  States Facing  98 

Graphite  Coal  in  Rhode  Island  and  Massachusetts 98 

Anthracite  Coal-beds  of  Pennsylvania 99 

Semi-anthracite  in  Sullivan  Co.,  Pa 100 

Progression  from  Bituminous  to  Anthracite 101 

Early  Use  of  Pennsylvania  Anthracite 101 


CONTENTS.  ix 

PAGE 

Virginia  Anthracite 102 

Anthracite  in  Colorado 103 

Anthracite  in  New  Mexico 103 

Bituminous  and  Semi-Bituminous  Coal-fields 103 

Appalachian  Field  in  Pennsylvania 104 

Analyses  of  Pennsylvania  Bituminous  and  Semi-bituminous  Coals 107 

Maryland  Semi-bituminous  Coal 110 

Virginia Ill 

North  Carolina 112 

West  Virginia 112 

Eastern  Kentucky 114 

Tennessee 116 

Georgia,  Alabama 117 

Ohio 118 

Northern  or  Michigan  Coal-field 119 

The  Illinois  Coal-basin 120 

Indiana 120 

Western  Kentucky 121 

Illinois 122 

The  Missouri  Coal-basin 124 

Iowa,  Missouri 125 

Kansas 126 

Arkansas 127 

Oklahoma 128 

Texas 129 

Colorado 131 

New  Mexico,  Wyoming 132 

Montana 133 

Utah,  Washington 134 

Alaska : 136 

Texas  Lignite 137 

Lignites  and  Lignitic  Coals  of  the  Western  States 137 

Arizona  Lignite 138 

Idaho,  North  Dakota,  Nevada 139 

California,  Oregon 139 

CHAPTER  V. 

TESTS   OF   THE   HEATING   VALUE   OP   AMERICAN   AND   FOREIGN   COALS. 

Johnson's  Tests  of  American  Coals 141 

Scheurer-Kestner's  Tests  of  European  Coals 141 

Mahler's  Tests  of  European  Coals 141 

Mahler's  Bomb-calorimeter 144 

The  Parr  Calorimeter 152 

Lord  and  Haas's  Tests  of  American  Coals 153 

Comparison  of  Mahler's  and  Lord  and  Haas's  Results 158 

Heating  Value  of  Wyoming  Coals 160 


X  CONTENTS. 

PAGE 

Calorific  Power  of  Weathered  Coals 161 

Weathering  of  Coal 165 

Deterioration  of  Coal  in  Storage 165 

CHAPTER  VI. 

FUELS  OTHER  THAN  COAL. 

Coke 167 

Pressed  Fuel  or  Briquettes 167 

Coal-dust,  Powdered  Fuel 170 

Peat  or  Turf 172 

Wood 174 

Sawdust 175 

Tan-bark 176 

Straw 177 

Bagasse 178 

Petroleum 180 

Oil  versus  Coal  as  Fuel 188 

Specifications  for  Purchase  of  Oil 189 

Tar  as  Fuel 190 

Gas  Fuel 191 

Corn  as  Fuel . 193 

CHAPTER  VII. 

FURNACES, METHODS   OF   FIRING. SMOKE-PREVENTION. MECHANICAL    STOKERS. 

FORCED  DRAFT. 

Location  of  the  Furnace 195 

Requirements  of  a  Good  Furnace 197 

Burning  of  Anthracite  Coal 197 

Burning  Small  Sizes  of  Anthracite 198 

Comparative  Efficiency  of  Steam-  and  Fan-blowers 200 

Grate-bars 201 

Shaking-  and  Dumping-grates 203 

The  McClave  Grate. 205 

The  Argand  Steam-blower 206 

How  to  Burn  Soft  Coal 207 

How  to  Avoid  Smoke 209 

Practical  Success  of  Smoke-prevention . . .  • 209 

The  Coking  System  of  Firing 211 

Alternate  Firing 212 

The  "Wing-wall"  Furnace 213 

Introduction  of  Heated  Air  into  the  Furnace 215 

Steam-jet  Smoke  Preventers 215 

Downward-draft  Furnaces 218 

Automatic  or  Mechanical  Stokers 219 

The  Playford  Stoker 221 


CONTENTS.  xi 

PAGE 

The  Babcock  &  Wilcox  Stoker 222 

The  Roney  Stoker 225 

The  Murphy  Furnace 226 

The  Jones  Under-feed  Stoker 227 

The  Taylor  Gravity  Underfeed  Stoker 228 

The  Riley  Underfeed  Stoker.  .  .  230 

Burning  Illinois  Coal  Without  Smoke \ 232 

Forced  Draft 234 

Effect  of  Damper  Regulation 236 

Economy  of  High  Rates  of  Driving 237 

Relation  of  Draft  to  Boiler  Capacity 238 

The  Howden  Hot-air  System ' 239 

The  Prat  Induced  Draft  System 239 

Retarders 240 

The  Ellis  &  Eaves  Hot-air  System 240 

Calculations  for  Forced  Draft 240 

Furnaces  for  Burning  Coal-dust 245 

Methods  of  Burning  Petroleum 248 

Mechanical  Oil  Burners . : 253 

Methods  of  Burning  Tar 259 

Bagasse  Burner 260 

Furnaces  for  Burning  Wood,  Sawdust,  etc 261 

Furnaces  for  Burning  Wet  Tan 264 

Volume  of  Combustion  Space  Required 266 

CHAPTER  VIII. 

SOME  ELEMENTARY  PRINCIPLES  OF  BOILER  ECONOMY  AND  CAPACITY. THE  PLAIN 

CYLINDER   BOILER. 

Capacity  of  a  Plain  Cylinder  Boiler 269 

Calculations  of  Fuel  Economy 272 

Capacity  Depends  on  Economy 273 

Loss  of  Economy  due  to  Insufficient  Heating  Surface 276 

Maximum  Possible  Economy 277 

Loss  of  Heat  by  Radiation 279 

Capacity  of  a  Plain  Cylinder  Boiler  at  Different  Rates  of  Driving 281 

Disadvantages  of  the  Plain  Cylinder  J3oiler 282 

Saving  Waste  Heat  of  the  Plain  Cylinder  Boiler 283 

Use  of  a  Water-Tube  Boiler  as  an  Addition  to  the  Plain  Cylinder  Boiler .  . .   283 

CHAPTER  IX. 

EFFICIENCY   OF   THE    HEATING    SURFACE. 

Statement  of  the  Problem 285 

Radiation  Considered 291 

General  Formulas  for  Efficiency 294 

Interpretation  of  the  Equation 294 


xii  CONTENTS. 

PAGE 

The  Coefficient  a  as  a  Criterion  of  Boiler  Performance 295 

Effect  of  Variation  of  the  Conditions 296 

Effect  of  Heating  Value  of  the  Fuel 298 

Effect  of  Hydrogen  and  Moisture 300 

Loss  of  Efficiency  due  to  Moisture  in  the  Air 300 

Practical  Conclusions  from  the  Discussion 301 

Low  Temperature  of  Furnace  may  Cause  High  Flue  Temperature 307 

Relation  of  Furnace  Temperature  to  Heating  Surface  Required 308 

Heat  Transmitted  by  Successive  Portions  of  the  Surface 310 

Efficiencies   and  Flue  Temperatures  for  Varying  Air  Supply  and  Rate  of 

Driving 314 

Modification  of  Formula  (15)  for  Incomplete  Combustion 315 

Meaning  of  the  Coefficient  a\ 317 

Values  of  a\  computed  from  Boiler  Trials 319 

Calculations  of  Efficiency  by  the  Revised  Formula 320 

Effect  of  Quality  of  Coal  upon  Efficiency 322 

Efficiencies  Obtained  in  Practice 322 

The  Straight-line  Formula  for  Efficiency 323 

Blechynden's  Experiments  on  Transmission  of  Heat 325 

Durston's  Experiments  on  Transmission  of  Heat ' 329 

Effect  of  Circulation  on  Economy 330 

Efficiency  does  not  Depend  on  Type  of  Boiler 332 

Comparison  of  Lancashire  and  Multitubular  Boilers 333 

Effect  of  Velocity  of  Gases  on  Efficiency 334 


CHAPTER  X. 

TYPES    OF    STEAM-BOILERS. 

Evolution  of  Different  forms  of  Boiler 341 

Two-flue  Boiler , 342 

Evolution  of  the  Steam-boiler  in  France  and  England 342 

The  Cornish  Boiler '.  ...  342 

The  Lancashire  and  Galloway  Boilers 343 

The  Horizontal  Return-flue  Boiler 344 

The  Vertical  Tubular  Boiler 346 

The  Locomotive  Boiler 348 

The  Scotch  Marine  Boiler. 349 

The  Water-tube  Boiler 351 

Early  Forms  of  Water-tube  Boiler 352 

More  Recent  Forms  of  Water-tube  Boiler 353 

Modern  Forms  of  Water-tube  Boiler 354 

Setting  of  a  Heine  Boiler  with  Superheater 365 

Water-tube  Marine  Boilers 370 

Forms  of  Boiler  Used  in  Different  Countries  . .  .  374 


CONTENTS.  xiii 


CHAPTER  XI. 

THE   HORSE-POWER  OF  A  STEAM-BOILER. — PROPORTIONS  OF  HEATING  AND    GRATE- 
SURFACE. PERFORMANCE  OF  BOILERS. 

PAGE 

The  Horse-power  of  a  Steam-Boiler 376 

Definitions  of  Boiler  Horse-power 377 

Measures  for  Comparing  the  Duty  of  Boilers 378 

Proportions  of  Grate  and  Heating  Surface  for  a  Given  Horse-power 379 

Heating  Surface 379 

Measurement  of  Heating  Surface 381 

Ratio  of  Superheating  Surface  to  Boiler  Surface 382 

Horse-power,  Builder's  Rating 382 

Grate-surface 383 

Areas  of  Flues  and  Gas-passages 385 

Air-passages  through  Grate-bars 386 

Performance  of  Boilers .386 


CHAPTER  XII. 

POINTS    OF    A    GOOD    BOILER. 

Selecting  a  New  Type  of  Boiler.  .  , 388 

Economy  of  Fuel 389 

Danger  of  Explosion 391 

Durability 392 

Facility  for  Removal  of  Scale 393 

Water  and  Steam  Capacity 394 

Steadiness  of  Water-level 395 

Dryness  of  Steam 395 

Water  Circulation 396 

CHAPTER  XIII. 

BOILER   DESIGN   AND    CONSTRUCTION. 

Boiler  and  Boiler  Plant  Design 397 

Modern  Boiler  Plants 399 

A  Large  Boiler  Plant  in  France 401 

Station  of  the  Commonwealth  Edison  Co.,  Chicago 402 

Designing  Boilers  for  a  Street  Railway  Plant 403 

Materials  Used  in  Boilers 412 

Boiler  Tubes 416 

Shells,  Water  and  Steam  Drums 418 

Riveted  Joints 418 

Convex  or  Bumped  Heads 422 

Thickness  of  Plates,  Riveting 422 

Working  Pressure  on  Boilers  with  Triple-riveted  Joints 424 


xiv  CONTENTS. 

PAGE 

Pressures  Allowed  on  Boilers 425 

Making  a  Boiler  Shell 426 

Holding  Power  of  Expanded  Tubes 428 

Calking 428 

Braces  and  Stays 429 

Stay-bolts 431 

Flat  Surfaces  Supported  by  Stay-bolts 432 

Size  of  Boiler  Tubes 435 

Tube  Spacing  in  Horizontal  Tubular  Boilers 437 

Manholes  and  Handholes t 437 

Dimensions  of  Boilers ; 439 

Sizes  of  Water-tube  Boilers 441 

Specifications  for  Horizontal  Tubular  Boilers 442 

Setting  of  a  Horizontal  Tubular  Boiler 452 

Fire-brick  Furnace  Arches 458 

Hollow  Walls  not  an  Advantage 459 

Fire-brick  for  Furnaces 460 


CHAPTER  XIV. 

BOILER    ATTACHMENTS    AND    BOILER-ROOM    APPLIANCES. 

Mud  Drums 461 

Blow-off  Pipe;  Blow-Off  Valve 462 

Steam  Dome 462 

Dry  Pipe 463 

Connecting  Steam  Pipes  to  Boilers 463 

Fire  Doors 464 

Fire-door  Openings 465 

Nozzles  for  Attaching  Pipes  to  Boilers 466 

Brackets  and  Hangers  for  Supporting  Boilers 466 

Feeding  Boilers 467 

Attachments  to  Boilers 467 

Safety  Valves 469 

Damper  Regulators 474 

Feed- water  Regulator 474 

Blow-off  Valve 476 

Surface  Blow-Off 477 

Regulating  the  Air  Supply  Over  the  Fire 477 

Water-tube  Cleaner 478 

Steam  Separators 478 

High-  and  Low-water  Alarm 479 

Gauge  Glass  and  Gauge  Cocks 479 

Steam  Gauges 480 

The  Venturi  Meter 480 

The  V-Notch  Water  Meter 481 

Feed-water  Indicators .  4 


CONTENTS.  xv 

PAGE 

Filtering  Oil  from  Feed  Water 483 

Steam  Meters : 484 

The  Roberts  Smoke  Chart 488 

Differential  Draft  Gauges 488 

The  Uehling  Triple  Draft  Gauge 490 

Flue  Gas  Analysis 491 

Co2  Recorders 492 

The  Uehling  Pyrometer 494 

Piping  Connections  for  CO2  Recorders . 494 

The  Bi-Meter  CO2  Recorder 496 

Oxygen  Recorder 497 

Superheating  of  Steam 498 

The  Foster  Superheater 499 


CHAPTER  XV. 

BOILER   TROUBLES    AND    BOILER-USERS'    COMP1\AINTS. 

Causes  of  Complaint 501 

Poor  Draft 501 

Insufficient  Grate-surface  and  Poor  Coal 503 

Furnace  not  Adapted  to  Coal 503 

Bad  Setting  of  Boiler 504 

Leaks  of  Air  Through  Brickwork 506 

Improper  Firing 507 

Insufficient  Heating  Surface '. 511 

Bad  Water 512 

Corrosion,  Internal 513 

Use  of  Zinc  as  a  Remedy  for  Corrosion 515 

Incrustation  or  Scale 518 

Effect  of  Scale  on  Boiler  Efficiency 520 

Boiler-compounds 523 

Causes  and  Remedies  for  Incrustation 524 

The  Use  of  Boiler-compounds 527 

Chemical  Theory  of  Scale  Remedies 527 

Water-softening  Apparatus 535 

Method  of  Testing  Boiler  Waters 536 

Methods  for  Purification  of  Water 538 

The  Permutit  Water-softening  Process 544 

External  Corrosion 546 

The  Life  of  a  Steam-boiler 547 

Defects  Discovered  by  Inspection 547 

Explosions  Caused  by  Hidden  Defects 547 

Causes  of  Boiler  Explosions 550 

Clinkering  in  Furnaces 553 


xvi  CONTENTS. 

CHAPTER  XVI. 

EVAPORATION   TESTS   OF    STEAM-BOILERS. 

PAGE 

Object  of  an  Evaporation  Test 557 

Rules  for  Conducting  Boiler  Trials,  Code  of  1915 559 

Forms  for  Report  of  a  Trial 572 

Appendices  to  Code 576 

Computation  of  the  Results  of  a  Boiler  Trial 591 

Erroneous  Conclusions  from  Boiler  Tests 594 

CHAPTER  XVII. 

RESULTS    OF    STEAM-BOILER   TRIALS. 

Range  of  Economy  Found  in  Practice 596 

Tests  of  Stirling  Boilers  with  Anthracite  Coal ". 598 

Comparative  Trials  of  Two-flue  Boilers  with  Pittsburg  Coal 603 

Tests  of  a  Babcock  &  Wilcox  Marine  Boiler 605 

Tests  of  a  Thorny  croft  Boiler 607 

A  Study  of  Gas  Analyses 610 

Tests  of  a  Mosher  Marine  Boiler 611 

Tests  of  Large  Boilers  of  the  Detroit  Edison  Co 612 

Comparison  of  Three  High  Records ..." 617 

Tests  of  a  Locomotive 618 

Application  of  the  Criterion  Formula 622 

Range  of  Results  Obtained  from  Anthracite  Coal 623 

Tests  With  Anthracite  at  the  Centennial  Exhibition 624 

Highest  Efficiency  with  Anthracite 629 

Impossible  Boiler  Performances 629 

Test  of  a  Rust  Water-tube  Boiler  with  Pittsburgh  Coal 630 

Test  of  a  Babcock  &  Wilcox  Boiler  and  Taylor  Stoker 632 

Tests  with  Taylor  Stokers '. 633 

Test  of  an  Edge  Moor  Water-tube  Boiler 635 

Recent  Experience  with  the  Delray  (Detroit)  Boilers 638 

Labor  Costs  at  the  Delray  Plant 639 

Tests  of  Riley  Underfeed  Stokers 640 

High  Rates  of  Driving  Fire-Engine  Boilers 641 

Variation  in  Gas  Analyses 641 

Relation  of  CO2,  O  and  CO  in  94  Tests 644 

Air  Leaks  Through  Boiler  Settings 645 

Tests  of  Washed  Grades  of  Illinois  Coal 645 

Tests  with  North  Dakota  Lignite 646 

Tests  with  Coke-oven  and  Blast-furnace  Gas 648 

Tests  with  Oil  Fuels 648 

Tests  of  Two  Kinds  of  Tile  Roof 652 

Superheated  Steam  in  Locomotive  Service 655 

Tests  with  Natural  Gas  as  Fuel.  .  .  657 


CONTENTS.  xvii 


CHAPTER  XVIII. 

PROPERTIES    OP    WATER    AND     STEAM. — FACTORS    OF    EVAPORATION. CHIMNEYS. 

«  PAGE 

Properties  of  Water 658 

Weight  and  Heat-units  of  Water 659 

Properties  of  Steam 660 

Steam-Table 662 

Properties  of  Superheated  Steam 665 

Factors  of  Evaporation 667 

Chimney-draft  Theory 671 

Height  of  Chimney  for  Different  Fuels 676 

Table  of  Sizes  of  Chimneys 679 

Velocity  of  Gas  in  Chimneys 680 

Chimneys  with  Forced  Draft 680 

Chimneys  for  Mechanical  Stoker  Installations 681 

Chimney  Table  for  Oil  Fuel 681 

Regulation  of  Draft  with  Variable  Loads  and  Oil  Firing 683 

Lightning  Conductors 684 

Design  of  Breechings  and  Smoke  Flues 684 

Radial  Brick  Chimneys 686 

Concrete  Chimneys 687 

CHAPTER  XIX. 

MISCELLANEOUS. 

Economizers 689 

The  "  Unaccounted  For  Loss  "  in  the  Heat  Balance 696 

Loss  of  Fuel  Due  to  Banking  Fires 697 

Coal  Used  in  Banking  Fires 698 

Cost  of  Coal  Per  Boiler  Horse-power 699 

Boiler-room  Labor 699 

Number  of  Boilers  to  Operate  with  Variable  Load 700 

Task  Setting  for  Firemen 701 

Results  of  Bonus  Payments  of  Labor 706 

Steam-boiler  Practice  of  the  Future. ,          , , 707 


STEAM-BOILER   ECONOMY. 


CHAPTER  I. 
PRINCIPLES    AND    DEFINITIONS. 

A  Steam-boiler  is  a  vessel  in  which,  by  the  agency  of  heat  derived 
from  the  combustion  of  fuel,  water  is  converted  into  steam. 

The  study  of  the  operation  of  a  steam-boiler  includes  the  consid- 
eration of  the  following  subjects: 

1.  The  fuel,  its  kind,  quality,  and  chemical  composition. 

2.  The  air  supplied  to  the  fuel  to  effect  its  combustion  or  rapid 
oxidation,  also  the  moisture  in  the  air. 

3.  The  furnace  in  which  the  combustion,  more  or  less  complete, 
takes  place;  its  construction  and  its  fuel-burning  capacity. 

4.  The  loss  of  unburned  fuel  through  the  grate-bars  of  the  fur- 
nace, or  in  the  ashes  withdrawn  from  it. 

5.  The  heat  generated  by  the  combustion;  its  quantity;  the  tem- 
perature attained  in  and  beyond  the  furnace ;  and  the  efficiency  of  the 
combustion,  or  the  ratio  which  the  quantity  of  heat  actually  generated 
bears  to  that  which  might  be  generated  with  perfect  combustion. 

6.  The  gaseous  products  of  combustion,  and  their  dilution  by  an 
excessive  supply  of  air. 

7.  The  transfer  of  heat  from  the  fire,  and  from  the  hot  gases 
generated  by  the  combustion,  through  the  shell  or  tubes  of  the  boiler 
into  the  water,  and  the  conditions  which  increase  or  diminish  the  rate 
and  the  effectiveness  of  the  transfer. 

8.  The  loss  of  heat  due  to  the  escape  of  hot  gases  into  the  flue  or 
chimney. 

9.  The  loss  of  heat  due  to  radiation  from  the  external  surfaces  of 
the  furnace  and  boiler. 

10.  The  properties  of  water  and  steam  at  different  temperatures. 


STEAM-BOILER  ECONOMY. 


11.  The  capacity  of  the  boiler,  or  the  quantity  of  water  it  is 
capable  of  converting  into  steam  under  certain  given  or  assumed  con- 
ditions. 

12.  The  efficiency  of  the  boiler,  or  the  ratio  of  the  heat  absorbed 
by  the  boiler  to  the  heat  which  would  be  generated  by  the  complete 
combustion  of  so  much  of  the  fuel  as  is  actually  burned. 

13.  The  efficiency  of  the  boiler  and  furnace  combined,  or  the  ratio 
of  the  heat  absorbed  by  the  boiler  to  the  heat  which  would  be  gener- 
ated by  complete  combustion  of  all  the  fuel  used,  including  that  lost 
through  the  grates  and  withdrawn  in  the  ashes. 

The  consideration  of  each  one  of  the  several  items  specified  above 
is  necessary  to  a  thorough  understanding  of  the  operation  and  the 
fuel  economy  of  a  steam-boiler,  and  each  will  be  discussed  at  length 
in  succeeding  chapters  of  this  book. 

The  general  subject  of  steam-boiler  economy,  however,  includes 
other  subjects  than  those  relating  to  fuel  economy,  such  as  the  con- 
struction of  the  boiler  in  its  relation  to  strength,  durability,  repairs, 
facility  of  cleaning,  space  occupied,  first  cost,  cost  of  labor  for  its 
operation,  etc.  These  will  also  be  treated  of  in  their  proper  place. 

Heat  is  a  form  of  energy  in  bodies,  supposed  to  consist  of  molec- 
ular vibration.  Its  nature,  like  that  of  gravity  and  electricity,  is  not 
clearly  understood,  but  its  effects  may  be  perceived  and  measured. 
Its  intensity  in  any  body  may  be  measured  in  degrees  of  temperature 
by  a  thermometer  or  pyrometer.  Its  quantity  may  be  measured  in 
heat-units.  When  two  bodies,  one  hotter  or  at  a  higher  temperature 
than  the  other,  are  placed  in  contact,  there  is  a  flow  of  heat  from  the 
hotter  into  the  cooler  body,  tending  to  equalize  their  temperature,  and 
the  quantity  of  heat  thus  transferred  may  be  measured  or  estimated  if 
the  nature  or  composition,  the  weight,  and  the  temperature  of  the  two 
bodies  are  known.  One  or  both  the  bodies  may  experience  a  change 
of  state  by  reason  of  the  transfer  of  heat.  Thus  if  a  piece  of  ice  be 
plunged  into  a  vessel  containing  steam,  the  flow  of  heat  from  the 
steam  will  condense  it  into  water,  and  the  flow  of  heat  into  the  ice 
will  cause  the  latter  to  melt  and  be  changed  also  into  water. 

Temperature,  or  intensity  of  heat,  is  measured  in  degrees,  by  a 
thermometer  or  pyrometer.  Certain  fixed  or  standard  temperatures 
are  identified  by  certain  phenomena  of  the  change  of  state  of  certain 
bodies.  The  two  most  commonly  used  standard  temperatures  are:  (1) 
that  of  melting  ice,  zero  on  the  Centigrade  thermometric  scale  or  32° 
on  the  Fahrenheit  scale,  and  (2)  that  of  the  boiling-point  of  pure 


PRINCIPLES  AND  DEFINITIONS.  3 

water  at  the  mean  atmospheric  pressure  of  14.7  Ibs.  per  square  inch, 
viz.,  100°  on  the  Centigrade  scale  or  212°  on  the  Fahrenheit  scale. 
The  Fahrenheit  scale  is  most  commonly  used  in  England  and  the 
United  States.  If  the  range  of  temperature  between  the  freezing  and 
the  boiling-points  of  water  be  divided  into  180  equal  parts,  we  obtain 
the  scale  of  degrees  of  the  Fahrenheit  thermometer,  which  scale  may 
be  extended  indefinitely  downwards  and  upwards  to  measure  the  low- 
est and  the  highest  temperatures  found  in  the  arts.  For  scientific 
measurements  of  great  accuracy  and  through  a  wide  range  degrees 
of  temperature  may  be  measured  by  the  air-thermometer,  in  which 
the  recorded  degree  of  temperature  is  proportional  to  the  product  of 
the  pressure  and  volume  of  a  given  weight  of  air.*  For  all  ordinary 
purposes  the  mercury  thermometer  is  available  between  the  range  of 
—  40°  and  600°  F.,  and  mercury  thermometers  with  compressed 
nitrogen  in  the  tube  above  the  mercury  may  be  used  for  temperatures 
as  high  as  900°  or  1000°  F.  For  higher  temperatures,  up  to  3000° 
F.,  the  Uehling  and  Steinbart  air  pyrometer,  the  Chatelier  and  the 
Bristol  electric  pyrometers,  and  the  Fery  radiation  pyrometei  are 
available.  For  obtaining  the  temperature  of  chimney-gases,  from 
300°  to  1200°,  metallic  pyrometers  may  be  used,  but  their  indications 
are  apt  to  be  inaccurate. 

The  temperatures  commonly  observed  in  steam-boiler  practice  are, 
on  the  Fahrenheit  scale: 

1.  The   temperature   of  the  feed-water,   from   32°   to   300°   and 
upwards. 

2.  The  temperature  of  the  steam,  from  212°  to  400°  (correspond- 
ing to  saturated  steam  of  250  Ibs.  per  sq.  in.  absolute  pressure)  and 
upwards  (500°  or  over  for  highly  superheated  steam). 

3.  The  temperature  in  the  furnace,  from  1000°  to  3000°  or  up- 
wards. 

4.  The  temperature  of  the  escaping  flue-gases,  from  300°  to  1200° 
and  upwards. 

5.  Temperatures  of  the  gases  of  combustion,  taken  at  points  in 
the  gas-passages  through  the  boiler  intermediate  between  the  furnace 
and  the  flue. 

A  Heat-unit,  or  British  Thermal  Unit  (B.T.U.),  is  the  quantity 
of  heat  required  to  raise  the  temperature  of  one  pound  of  pure  water 

*  Consult  Rankine,  Steam-engine^  p.  226;    Kent's  Mech.  Engrs.  Pocket-book, 
8th  edition,  p.  530;  Trans.  A.S.  M.  E.,  vol.  vi.  p.  282. 


4  STEAM-BOILER  ECONOMY. 

one  degree  Fahrenheit,  or,  more  accurately,  1/180  of  the  heat  required 
to  raise  it  from  32°  to  212°  F. 

The  quantity  of  heat  required  to  raise  the  temperature  of  one 
pound  of  water  1°  F.  varies  very  slightly  with  the  temperature,  being 
nearly  constant  below  100°  F.  and  increasing  at  higher  temperatures, 
so  that  to  raise  its  temperature  from  32°  to  100°  requires  67.97 
instead  of  68  B.T.U.,  and  from  100°  to  300°,  201.6  instead  of  200 
B.T.U. 

The  Unit  of  Evaporation  (U.E.)  is  the  quantity  of  heat  required 
to  convert  one  pound  of  water  at  212°  into  steam  of  the  same  tem- 
perature. It  is  equivalent  to  970.4  B.T.U. 

Latent  Heat  is  the  quantity  of  heat  which  apparently  disappears 
(or  becomes  latent  or  hidden,  and  therefore  not  measurable  by  a 
thermometer)  when  a  body  changes  its  state  from  solid  to  liquid 
or  from  liquid  to  gaseous,  while  the  temperature  remains  constant. 
Thus  when  a  pound  of  ice  at  32°  is  converted  into  water  at  the  same 
temperature,  144  B.T.U.  becomes  latent,  and  when  a  pound  of  water 
at  212°  is  converted  into  steam  at  212°,  970.4  B.T.U.  (or  one  U.E.) 
becomes  latent. 

When  a  body  changes  its  state  from  the  gaseous  to  the  liquid 
form,  or  from  the  liquid  to  the  solid  form,  the  heat  which  was  latent 
is  given  off  and  becomes  sensible  heat.  Thus  a  pound  of  steam  at 
212°  in  condensing  to  water  at  212°  transfers  970.4  B.T.U.  to  sur- 
rounding bodies,  raising  their  temperature,  and  a  pound  of  water  at 
32°  freezing  into  ice  at  the  same  temperature  will  give  off  144  B.T.U. 
to  the  surrounding  atmosphere. 

Specific  Heat  is  a  figure  representing  the  quantity  of  heat,  ex- 
pressed in  thermal  units,  required  to  raise  the  temperature  of  one 
pound  of  any  given  substance  one  degree;  or  it  is  the  ratio  of  the 
quantity  of  heat  required  to  raise  the  temperature  of  a  given  weight 
of  the  substance  one  degree  to  the  quantity  required  to  raise  the  tem- 
perature of  the  same  weight  of  water  from  62°  to  63°  F.  The  specific 
heat  of  water  at  62°  F.  being  taken  at  unity,  that  of  all  other  known 
substances,  except  hydrogen,  is  less  than  unity. 

One  of  the  methods  of  determining  the  specific  heat  of  a  body  is 
the  method  by  mixture,  described  as  follows : 

The  body  whose  specific  heat  is  to  be  determined  is  raised  to  a 
known  temperature,  and  is  then  immersed  in  a  mass  of  liquid  of 
which  the  weight,  specific  heat,  and  temperature  are  known.  When 


PRINCIPLES  AND  DEFINITIONS.  5 

both  the  body  and  the  liquid  have  attained  the  same  temperature,  this 
is  carefully  ascertained. 

Now  the  quantity  of  heat  lost  by  the  body  is  the  same  as  the 
quantity  of  heat  absorbed  by  the  liquid. 

Let  c,  w,  and  i  be  the  specific  heat,  weight,  and  temperature  of  the 
hot  body,  and  c'  ,  w',  and  t'  of  the  liquid.  Let  T  be  the  temperature 
the  mixture  assumes. 

Then,  by  the  definition  of  specific  heat,  c  X  w  X  (t  —  T)  =  heat- 
units  lost  by  the  hot  body,  and  c'  X  w'  X  (T  —  t')  =  heat-units 
gained  by  the  cold  liquid.  If  there  is  no  heat  lost  by  radiation  or 
conduction,  these  must  be  equal,  and 

cw(t  -  T)  -  c'w'(T  -  t')     or    c 


The  specific  heats  of  several  different  substances  at  ordinary 
atmospheric  temperatures  are  given  below: 

SOLIDS. 

Copper  ....................  0.0951  Aluminum  ............       0.2185 

Glass  ..................  ____  0.  1937  Charcoal  .............       0.2410 

Iron,  cast  ..................  0.1298  Coal  .................  0.20  to  0.24 

Iron,  wrought  ..............  0.  1138  Coke  .................       0.203 

Steel,  soft  ..................  0.  1165  Brickwork  and  masonry  about  0.20 

Platinum  ..................  0.0324  Wood  ................  about  0.32 

LIQUIDS. 

Water  .....................   1  .0000        Mercury  ..................  0.0333 

GASES. 

At  Constant      At  Constant 
Pressure.  Volume. 

Steam,  superheated  *  .....................  0  .  4805  0  .  346 

Air  .........  ............................  0.2375  0.1685 

Oxygen  .................................  0.2175  0.1551 

Hydrogen  ...............................  3.4090  2.4122 

Nitrogen  ..............................  0.2438  0.1727 

Carbon  monoxide,  CO  ...................  0.2479  0.1758 

Carbon  dioxide,  CO2  .....................  0.217  0.  1710 

Marsh-gas  (methane),  CH4  ................  0.5929  0.4683 

Olefiant  gas  (ethylene),  C2H4  ..............  0.404  0.332 

Blast-furnace  gas  ........................  0  .  228 

Gases  in  chimneys  of  steam-boilers  (approx.)  .  0  .  240 

*  These  figures  are  from  Regnault'  sexperiments.  More  recent  determinations 
show  that  the  specific  heat  of  superheated  steam  varies  with  the  pressure  and 
temperature.  See  M.E.  Pocket-book,  p.  838. 


6  STEAM-BOILER  ECONOMY. 

The  specific  heat  of  a  gaseous  mixture,  such  as  that  of  a  chimney- 
gas,  is  found  by  multiplying  the  percentage  of  each  of  the  constituent 
gases  by  the  specific  heat  of  that  gas  and  dividing  the  sum  of  the 
products  by  100.  Thus  for  a  gas  whose  composition  is  C02,  12; 
CO,  0.5 ;  0,  9.5 ;  N,  78,  we  have 

CO2 ' 12     X0.217   =  2.604 

CO 0.5X0.248   =  0.124 

0 9.5X0.2375=  2.256 

N..  78     XO.  2438  =  19. 016 


100.0  24.000 

Whence  the  specific  heat  is 

24.0  +  100  =  0.240. 

The  specific  heats  of  all  substances  in  the  solid  or  liquid  state 
increase  slowly  as  the  temperature  rises.  Experiments  by  Mallard 
and  Le  Chatelier  indicate  a  continuous  increase  in  the  specific  heat  of 
C02,  steam,  and  other  gases  with  rise  of  temperature.  The  variation 
is  inappreciable  at  212°  F.,  but  increases  rapidly  at  high  temperatures. 
In  the  absence  of  data  of  specific  heats  of  gases  at  high  temperatures, 
the  figures  given  in  the  above  tables  are  generally  used  in  calculations 
relating  to  gases  of  combustion,  although  their  use  may  lead  to  errors 
of  unknown  magnitude  in  the  results.  (See  page  340.) 

The  following  figures,  showing  increase  of  specific  heat  of  metals 
with  rise  of  temperature,  are  sometimes  used  in  pyrometric  calcula- 
tions : 

Platinum,  22°  to  440°  F.,  0.0332,  increasing  0.000305  for  each  100°  F.  above  440°. 

Copper,  32°  to  212° 0.094 

32°  to  572° 0. 1013 

Wrought  iron,  32°  to  212° 0.1138 

"  32°  to  500° 0.1228 

"  32°  to  1300° 0.1601 

"  32°  to  1500° 0. 1698 

32°  to  2700° 0.1666 

The  Quantity  of  Heat  in  a  body,  in  British  thermal  units,  meas- 
ured above  a  certain  temperature  taken  as  standard,  usually  32°  F., 
is  the  product  of  its  weight,  its  average  specific  heat  between  the 
limits  of  temperature  considered,  and  the  difference  between  its  tem- 
perature and  the  standard  temperature.  Thus  the  quality  of  heat 
above  32°  in  a  piece  of  wrought  iron  weighing  10  Ibs.,  at  a  tempera- 
ture of  212°,  is  10  X  -1138  X  (212  —  32)  =  204.84  B.T.U. 


PRINCIPLES  AND  DEFINITIONS.  7 

This  statement  is  true,  however,  only  when  the  body  does  not 
change  its  state  between  the  standard  temperature  and  the  higher 
temperature.  When  the  body  changes  its  state,  its  latent  heat  must 
be  considered.  Thus  the  heat  above  32°  in  a  pound  of  steam  is  the 
sum  of 

Heat  required  to  raise  its  temperature  from  32°  to  212° 180 . 0  B.T.U. 

Latent  heat  of  evaporation  at  212° 970. 4      " 


Total i 1150.4      " 

The   quantity   of  heat  in  a  pound   of  saturated  steam  at   320°  F. 
(75.3  Ibs.  gauge  pressure  per  sq.  in.)  is 

Heat  (above  32°)  in  water  at  320° 290.5  B.T.U. 

Latent  heat  of  evaporation  at  320° 893.9 

Total 1184.4      " 

When  the  steam  is  superheated,  the  quantity  of  heat  required  for 
superheating  must  be  added.  Thus  if  the  steam  of  75.3  Ibs.  gauge 
pressure,  whose  temperature  when  saturated  is  320°,  be  superheated, 
while  its  pressure  remains  constant,  to  420°,  the  increase  of  100°  of 
temperature  will  require,  since  the  specific  heat  of  superheated  steam 
at  that  pressure  and  between  320°  and  420°  is  about  0.526,  an  addition 
of  52.6  B.T.U.,  making  the  total  heat  1184.4  +  52.6  =  1237  B.T.U. 
The  properties  of  steam  will  be  discussed  further  in  another  chapter. 

Heat  of  Combustion. — Every  combustible  chemical  element,  such 
as  carbon,  hydrogen,  and  sulphur,  and  every  gaseous  fuel  of  definite 
chemical  composition,  containing  two  or  more  elements,  such  as  car- 
bon monoxide  (CO)  and  methane  (marsh-gas,  CH4),  when  completely 
burned  in  oxygen  or  in  air  generates  a  definite  quantity  of  heat  per 
pound  of  the  combustible,  which  quantity  may  be  ascertained  with  a 
close  approximation  to  accuracy  by  means  of  an  instrument  known  as 
a  fuel  calorimeter.  The  exact  determination  of  the  heat  of  combus- 
tion, or  calorific  value,  of  any  combustible  requires  a  very  delicate 
apparatus,  a  high  degree  of  skill  on  the  part  of  the  operator,  and  an 
allowance  for  certain  unavoidable  errors,  such  as  loss  by  radiation, 
so  that  the  calorific  values  of  different  combustibles  as  reported  by 
different  authorities  show  a  slight  variation.  Thus  the  heating  value 
of  carbon  is  14,544  B.T.U.  according  to  Favre  and  Silbermann,  and 
14,647  B.T.U.  according  to  Berthelot.  That  of  hydrogen  is  62,032 
B.T.U.  according  to  Favre  and  Silbermann,  and  61,816  B.T.U.  accord- 


8  STEAM-BOILER  ECONOMY. 

ing  to  Thomsen.  The  round  figures  of  14,600  B.T.U.  for  carbon 
(burned  to  carbon  dioxide)  and  62,000  B.T.U.  for  hydrogen  (burned 
to  steam  and  the  steam  condensed  to  liquid  water)  are  generally  used 
in  calculations  relating  to  steam-boiler  practice. 

The  heating  value  of  any  fuel,  such  as  coal,  consisting  of  a  mixture 
of  combustible  and  non-combustible  substances  may  be  directly  deter- 
mined by  means  of  a  calorimeter,  or  it  may  be  calculated  from  its 
ultimate  chemical  analysis  by  Dulong's  formula,  which  is : 

Heating  value  =  -^  X  [l4,600C  +  62,(Wff  -  -|)  +  4000SJ, 

in  which  C,  H,  0,  and  S  are  the  percentages  of  carbon,  hydrogen, 
oxygen,  and  sulphur  in  the  coal,  as  determined  by  analysis. 

Combustion  of  Fuel. — Combustion  may  be  perfect  or  imperfect, 
depending  upon  the  supply  of  air  in  the  furnace  and  upon  other  con- 
ditions which  will  be  discussed  later.  When  the  combustion  is  perfect 
the  whole  of  the  carbon  in  the  fuel  is  burned  to  carbon  dioxide,  C02, 
each  pound  generating  14,600  B.T.U.,  and  the  whole  of  the  hydrogen 
is  burned  to  steam,  or  vapor  of  water,  H20,  each  pound  generating 
62,000  B.T.U.  Part  of  the  heat  of  the  combustion  of  hydrogen  is 
absorbed  in  the  latent  heat  of  evaporation  of  the  9  Ibs.  of  stea'm  formed 
by  the  combustion  of  1  Ib.  of  hydrogen,  and  another  part  in  super- 
heating, to  the  temperature  of  the  furnace,  this  steam,  and  also  the 
steam  that  may  be  derived  from  moisture  in  the  coal  or  in  the  air 
supplied  to  the  furnace. 

When  the  combustion  is  imperfect  part  of  the  carbon  may  be 
burned  only  to  carbon  monoxide,  CO,  generating  only  4450  B.T.U. 
per  pound ;  or  part  of  the  carbon  which  has  been  burned  on  the  grate 
to  C02  may  be  "unburned,"  being  converted  into  CO  on  passing 
through  a  bed  of  red-hot  coke,  absorbing  carbon  therefrom  by  the 
chemical  reaction  C02  +  C  =  2CO,  a  cooling  process,  absorbing 
10,150  B.T.U.  per  pound  of  the  C  originally  burned  to  C02.  Also, 
in  imperfect  combustion  some  of  the  hydrogen,  together  with  the 
carbon  with  which  it  is  combined  in  the  coal,  forming  the  "volatile 
matter,"  may  be  only  distilled  from  the  coal  and  not  burned,  or  the 
hydrogen  only  in  this  volatile  matter  may  be  burned,  leaving  the 
carbon,  in  the  form  of  soot  or  smoke,  to  be  carried  off  in  the  gases 
passing  out  of  the  furnace.  All  the  products  of  imperfect  combus- 
tion, the  carbon  monoxide,  the  hydrocarbon  gases  distilled  from  the 


PRINCIPLES  AND  DEFINITIONS.  9 

coal,  and  the  soot  or  smoke,  may  afterwards  be  burned  if  they  are 
carried  into  a  very  hot  chamber,  where  they  are  thoroughly  mixed 
with  a  sufficient  supply  of  highly  heated  air. 

How  Smoke  may  be  Burned. — This  last  statement  is  contrary  to 
that  made  by  Charles  Wye  Williams  in  his  treatise  "On  the  Combus- 
tion of  Coal  and  the  Prevention  of  Smoke,"  first  printed  about  sixty 
years  ago,  and  copied  extensively  by  later  writers,  viz.,  that  "When 
smoke  is  once  produced  in  a  furnace  or  flue,  it  is  as  impossible  to 
burn  it  or  convert  it  to  heating  purposes  as  it  would  be  to  convert 
the  smoke  issuing  from  the  flame  of  a  candle  to  the  purposes  of  heat 
or  light."  The  error  of  the  statement  made  by  Mr.  Williams  can  be 
easily  shown  by  a  simple  experiment  which  has  been  made  by  the 
author.  A  short  piece  of  candle  was  placed  inside  of  a  tall,  narrow  tin 
cylinder.  The  deficient  supply  of  air  the  candle  thus  received  caused 
it  to  give  off  a  column  of  black  smoke.  This  was  caused  to  pass  into 
the  central-draft  tube  of  a  "Rochester"  kerosene  lamp,  and  as  it  passed 
up  into  the  flame  of  the  lamp  it  was  completely  burned,  not  a  trace 
of  smoke  being  visible  in  the  lamp-chimney.  The  experiment  was  also 
made  with  a  still  larger  column  of  smoke,  produced  bv  burning  paper 
under  the  lamp,  with  the  same  result. 

Flame  is  a  mass  of  intensely  heated  combustible  gas.  It  is  not 
necessarily  gas  in  a  state  of  combustion,  for  combustion  cannot  take 
place  without  access  of  air,  and  flame  may  exist,  as  in  passing  through 
a  furnace  or  flue,  where  there  is  no  supply  of  air  to  burn  the  gas.  If 
the  flame  in  passing  through  a  tube  becomes  cooled  below  a  bright  red 
heat,  the  gas  will  not  burn  when  it  escapes  and  comes  in  contact  with 
cool  air,  but  will  be  chilled  and  pass  off  as  unburned  gas  and  smoke. 

The  flame  of  pure  hydrogen  gas  is  almost  invisible,  but  visibility 
and  color  may  be  given  to  it  by  the  presence  of  other  substances; 
thus  carbon  will  make  it  white,  copper  green,  cyanogen  purple,  and 
sodium  yellow. 

The  white  color  of  the  flame  of  hydrocarbon  gas,  such  as  that  from 
a  candle  or  that  of  a  kerosene  lamp,  is  due  to  intensely  heated  particles 
of  carbon.  If  the  flame  is  caused  to  impinge  on  a  cold  surface,  some 
of  these  particles  will  be  deposited  as  soot. 

Visible  flame  is  evidence  of  imperfect  combustion  or  non-combus- 
tion. The  product  of  the  perfect  combustion  of  carbon  is  invisible 
carbon  dioxide  gas,  and  that  of  hydrogen  is  invisible  vapor  of  water. 

Take  a  lighted  central-draft  kerosene  lamp  and  adjust  the  wick  to 
such  a  point  that  the  lamp  gives  a  rather  short  and  clear  white  light 


10  STEAM-BOILER  ECONOMY. 

without  a  trace  of  smoke.  Now,  without  altering  the  adjustment  of 
the  wick,  gradually  obstruct  the  opening  at  the  bottom  of  the  central- 
draft-tube  and  observe  the  result.  The  flame  grows  longer  and  its 
whiteness  changes  to  yellow  and  then  to  red.  It  begins  to  smoke,  and 
finally  when  the  supply  of  air  is  nearly  shut  off  the  flame  has  risen  to 
nearly  the  top  of  the  chimney  and  a  dense  column  of  black  smoke  and 
soot  is  given  off.  We  learn  from  this  experiment  that  with  the  same 
consumption  of  fuel,  i.e.,  the  oil  supplied  by  the  wick,  the  flame  may 
'be  short  and"  intensely  hot,  or  very  long,  of  a  low  temperature,  smoky 
and  sooty.  While  the  flame  is  lengthening  and  before  it  becomes 
smoky  the  combustion  may  be  complete,  but  it  is  not  effected  in  as 
short  a  space  as  it  was  with  the  original  supply  of  air.  For  a  given 
supply  of  fuel  a  short  flame  means  rapid  and  complete  combustion,  a 
longer  flame  delayed  combustion,  and  a  very  long  flame  imperfect 
combustion.  If  midway  in  the  flame  of  medium  length  a  cool  surface 
be  interposed,  the  temperature  of  the  flame  will  be  lowered,  the  com- 
bustion will  be  rendered  imperfect,  and  smoke  and  soot  will  be 
produced. 

The  principles  learned  from  these  simple  experiments  with  the 
flame  of  a  lamp  are  of  great  importance  in  connection  with  the  study 
of  the  action  of  steam-boiler  furnaces. 

A  Transfer  of  Heat  from  the  burning  fuel  and  from  the  hot  gases 
produced  by  its  combustion  into  the  water  contained  in  a  steam-boiler 
takes  place  through  the  metal  plates  and  tubes  of  the  boiler  in  two 
ways:  (1)  by  radiation  directly  from  the  fire  and  from  the  hot  par- 
ticles of  carbon  in  the  flame,  and  (2)  by  contact  of  the  hot  gases  with 
the  metal  of  the  boiler.  The  laws  of  these  two  methods  of  transfer  are 
as  yet  imperfectly  understood,  and  there  is  a  great  lack  of  accurate 
scientific  data  concerning  them.  The  experimental  determination  of 
these  data  is  a  matter  of  extreme  difficulty,  on  account  of  the  number 
of  variable  conditions  attending  the  experiments.  Such  conditions  are : 
the  extent  of  surface  exposed  to  direct  radiation;  the  temperature  of 
the  radiating  surfaces,  the  resistance  to  radiation  of  metal  plates 
in  different  conditions,  more  or  less  coated  with  scale  and  soot;  the 
manner  in  which  the  heated  gases  impinge  upon  the  shell  and  tubes ; 
the  triple  resistance  to  transfer  of  heat  from  the  gases  to  the  water, 
viz.,  the  resistances  of  the  external  and  internal  surfaces  of  the  metal, 
varying  with  their  condition,  and  the  resistance  of  the  metal  between 
these  surfaces,  varying  with  the  nature  of  the  metal  and  its  thickness ; 
the  influence  which  the  temperature  of  the  gases  on  one  side  of  the 


PRINCIPLES  AND  DEFINITIONS.  11 

plate  and  tubes,  steadily  decreasing  as  they  pass  from  the  furnace  to 
the  flue,  and  the  temperature  of  the  water  on  the  other,  sensibly  con- 
stant, have  upon  the  rate  of  transfer  of  heat  through  the  metal  and  its 
exterior  and  interior  surfaces.  Notwithstanding,  however,  the  lack 
of  accurate  knowledge  concerning  the  influence  of  these  several  vari- 
ables on  the  transfer  of  heat  in  steam-boilers,  enough  is  known  to 
enable  us  to  deduce  some  broad  general  laws,  and  to  express  some  of 
them  in  empirical  formula?,  so  that  boilers  may  intelligently  be 
designed  to  fill  given  requirements,  and  so  that  the  probable  perform- 
ance of  any  boiler  and  furnace  may  be  predicted  from  a  study  of  its 
design  and  dimensions,  when  the  character  of  the  fuel  is  known, 
within  limits  of  error  sufficiently  narrow  for  practical  purposes. 

The  Capacity  of  a  Boiler  is  its  capacity  for  producing  steam.  It 
may  be  expressed  in  the  number  of  heat-units  absorbed  by  the  boiler 
in  a  given  time,  such  as  one  second,  or  in  the  number  of  pounds  of 
water  converted  into  steam  in  an  hour. 

"Equivalent"  Evaporation. — Since  the  latter  number  will  depend 
upon  the  temperature  of  the  feed-water  and  upon  the  pressure  or 
temperature  of  the  steam,  it  is  customary  to  express  the  capacity  in 
terms  of  what  is  called  "equivalent  evaporation,"  that  is,  reducing  the 
number  of  pounds  of  steam  actually  generated  at  a  given  or  observed 
pressure  from  feed-water  of  an  observed  temperature,  into  the  equiva- 
lent evaporation  per  hour  from  feed- water  of  212°  into  steam  at  the 
same  temperature,  or,  as  it  is  commonly  expressed,  "equivalent 
evaporation  per  hour  from  and  at  212°." 

The  evaporation  of  a  pound  of  water  from  and  at  212°  being  the 
"unit  of  evaporation"  (U.E.),  equal  to  970.4  B.T.U.,  the  capacity  of 
a  boiler  may  be  stated  as  so  many  U.  E.  per  hour. 

Boiler  Horse-power. — Another  convenient  method  of  expressing 
the  capacity  of  a  boiler  is  in  terms  of  "Boiler  Horse-power,"  a  boiler 
horse-power  being  equal,  according  to  a  commonly  accepted  conven- 
tion, to  34J  U.E.  per  hour,  or  34j  Ibs.  of  water  evaporated  from  and 
at  212°  per  hour.  This  latter  is  the  usual  method  of  expressing  the 
capacity  of  stationary  boilers  in  the  United  States.  It  is  not  used  for 
marine  or  locomotive  boilers. 

A  boiler  rated  at  100  H.P.  would  therefore  be  rated  also  at  a 
capacity  of  3450  Ibs.  of  water  from  and  at  212°  per  hour,  or  at 
3,347,880  B.T.U.  per  hour,  or  930  B.T.U.  per  second.  The  B.T.U. 
rating  is  not  used  in  practice,  as  it  is  not  so  convenient  as  the  other 
:methods  of  rating. 


12  STEAM-BOILER  ECONOMY. 

It  is  to  be  noted  that  the  "rating"  of  a  boiler  as  100  H.P.  may 
be  very  different  from  the  actual  capacity  it  may  show  under  a  given 
set  of  conditions.  The  "rating"  is  supposed  to  be  its  average  capacity 
under  easy  conditions  of  driving,  with  fairly  good  fuel,  and  with 
ordinary  draft.  Two  boilers  exactly  alike  in  all  respects  may  both  be 
rated  at  100  H.P.,  and  one  of  them  with  excellent  fuel  and  forced 
draft  may  be  actually  developing  200  H.P.,  while  the  other,  with  poor 
fuel  or  insufficient  draft  or  both,  may  not  be  capable  of  developing 
over  75  H.P. 

The  Efficiency  of  a  Boiler  may  mean:  1.  The  ratio  of  the  heat 
absorbed  by  it  to  the  heat  actually  generated  in  the  furnace;  2.  The 
ratio  of  the  heat  absorbed  by  it  to  the  heating  value  of  the  combustible 
actually  burned  (whether  thoroughly  or  not)  ;  3.  The  ratio  of  the 
heat  absorbed  by  it  to  the  heating  value  of  the  fuel  supplied  to  the 
furnace,  whether  all  the  fuel  is  burned  or  not  (some  of  the  fuel  may 
fall  through  the  grates  or  be  withdrawn  with  the  ashes,  and  not  be 
burned).  The  first  of  these  efficiencies  is  not  used  in  practice,  for  the 
reason  that  there  is  no  convenient  way  of  estimating  the  amount  of 
heat  actually  generated  in  the  furnace,  or  of  determining  what  portion 
of  the  fuel  is  imperfectly  burned.  The  second  and  third  are  com- 
monly used  and  are  thus  defined : 

„_  .  , ,    .,  Heat  absorbed  per  Ib.  combustible  burned 

Efficiency  of  boiler  = == — -r—   —~ .     „        — r- — -.T-J . 

Heating  value  01  1  Ib.  combustible 

Efficiency  of  boiler,  ^       Heat  absorbed  per  Ib.  coal  fired 
furnace,  and  grate  /  Heating  value  of  1  Ib.  coal 

The  meaning  of  the  word  "combustible"  in  the  above  definitions 
is  that  portion  of  the  total  fuel  supplied  to  the  furnace  which  remains 
after  deducting  its  moisture  (determined  by  a  test  of  a  sample)  and 
the  total  amount  of  ash  and  refuse  (including  unburned  coal)  with- 
drawn from  the  furnace,  through  the  grates  or  otherwise.  In  other 
words  it  is  the  sum  of  the  fixed  carbon  and  the  volatile  combustible 
matter,  or  the  "coal  dry  and  free  from  ash." 

The  Operation  of  a  Steam-boiler. — The  several  events  that  take 
place  in  the  operation  of  an  ordinary  steam-boiler  may  be  briefly 
described  as  follows:  Consider  that  the  furnace  is  already  heated,  a 
hot  fire  of  partially  burned  coal  or  coke  lying  on  the  grate,  and  that 
the  boiler  is  delivering  steam  as  usual.  A  few  shovelfuls  of  fresh  coal 
are  evenly  spread  over  the  bed  of  hot  coal,  to  replenish  the  fire.  The 
first  thing  that  then  takes  place  is  the  evaporation  of  the  moisture 


PRINCIPLES  AND  DEFINITIONS.  13 

contained  in  the  fresh  coal.  This  absorbs  heat  from  the  fire,  cooling 
it  for  a  short  time.  If  the  fresh  coal  is  of  small  size,  it  partly  fills 
the  interstices  between  the  pieces  of  hot  coal,  and  thereby  checks  the 
draft  and  diminishes  the  supply  of  air  which  enters  through  the  grate. 
The  formation  of  the  steam  by  the  evaporation  of  the  moisture  in 
the  fuel,  together  with  the  reduction  of  the  air-supply,  may  'cause 
two  chemical  actions  to  take  place  which  are  in  the  nature  of  "decom- 
position" or  the  reverse  of  combustion  or  rapid  oxidation,  both  of 
which  are  detrimental  to  the  most  economical  operation  of  the  boiler. 
The  first  is  the  decomposition  of  the  carbon  dioxide,  formed  by  the 
union  of  the  oxygen  of  the  air  with  the  carbon  of  the  hot  coal  lying 
next  to  the  grate  bars,  into  carbon  monoxide,  by  the  reaction  C02  +  C 
=  2  CO,  which  takes  place  when  carbon  dioxide  is  passed  through  a 
bed  of  very  hot  coal  or  coke,  the  supply  of  air  being  deficient.  The 
second  is  the  decomposition  of  a  portion  of  the  steam  produced  by  the 
evaporation  of  the  moisture  in  the  coal,  by  the  reaction  H20  +  C 
=  2H  +  CO,  which  takes  place  when  steam  is  brought  in  contact  with 
very  hot  carbon.  Both  of  these  reactions  or  decompositions  are  cool- 
ing processes,  absorbing  heat  from  the  fire,  and  they  therefore  dimin- 
ish the  rate  of  transfer  of  heat  through  the  heating  surface  of  the 
boiler.  Moreover,  they  both  rob  the  bed  of  fuel  of  some  of  its  carbon, 
converting  it  into  combustible  gases  which  may  escape  unburned,  thus 
causing  a  loss  of  heat.  Fortunately  the  length  of  time  during  which 
these  reactions,  unfavorable  to  economy,  take  place  is  not  long  when 
the  firing  is  done  carefully,  and  the  fresh  coal  is  fired  only  in  small 
quantities  at  a  time. 

After  the  moisture  is  driven  off  from  the  coal  the  volatile  matter 
begins  to  be  distilled,  and  this  continues  until  the  fresh  coal  has 
attained  a  red  heat.  When  the  amount  of  this  volatile  matter  is  small, 
when  the  air-supply  is  sufficient,  and  when  the  furnace  is  at  a  high 
temperature,  it  may  all  be  completely  burned  before  it  passes  out  of 
the  furnace;  but  if  it  is  distilled  in  large  volume  and  is  not  brought 
into  intimate  mixture  with  air  at  a  temperature  high  enough  to  main- 
tain ignition,  more  or  less  of  it  will  escape  unburned. 

After  the  volatile  matter  has  been  driven  off,  the  combustion  of 
the  remainder  of  the  coal  or  coke  is  completed.  If  the  relation  of  the 
thickness  of  the  bed  of  coal  on  the  grate  to  the  force  of  the  draft  is 
such  that  only  so  much  air  passes  through  the  grate  as  will  cause  the 
complete  combustion  of  the  carbon  to  C02,  the  temperature  of  the 
furnace  will  be  very  high,  a  most  favorable  condition  for  economy  of 


14  STEAM-BOILER  ECONOMY. 

the  boiler.  If  the  force  of  the  draft  be  excessive,  in  relation  to  the 
resistance  of  the  grate  and  the  fuel  upon  it  to  the  passage  of  air,  or  if 
the  bed  of  coal  be  too  thin,  an  excessive  supply  of  air  will  pass  into 
the  furnace,  lowering  its  temperature  and  making  conditions  unfavor- 
able to  economy.  If,  on  the  other  hand,  the  thickness  of  the  bed  of 
coal  is  too  great  in  its  relation  to  the  force  of  the  draft,  or  the  draft 
is  insufficient,  the  air  supply  to  the  furnace  will  not  be  enough  to 
secure  complete  combustion,  part  of  the  carbon  will"  be  burned  only  to 
CO,  and  the  furnace  temperature  will  be  low.  In  this  case  there  is 
thus  a  twofold  loss  of  economy;  first,  that  due  to  direct  loss  of  heat- 
units  by  imperfect  combustion;  and  second,  that  due  to  low  furnace 
temperature,  which  lessens  the  rate  of  transfer  of  heat  into  the  boiler. 

While  the  coal  is  being  burned  as  above  described  it  generates  a 
quantity  of  heat,  more  or  less  according  to  the  degree  of  completeness 
of  combustion,  at  a  rate  varying  from  one  instant  to  another  as  the 
conditions  vary,  the  coal  giving  off  moisture  at  one  period,  distilling 
its  volatile  matter  at  another,  and  having  its  carbon  burned  more  or 
less  perfectly  at  another.  The  temperature  of  the  furnace  also  varies 
as  these  conditions  vary,  and  with  it  the  rate  of  transfer  of  heat  into 
the  boiler  both  by  radiation  and  by  conduction. 

A  portion  of  the  heat  generated  in  the  furnace  being  radiated 
directly  from  it  into  the  boiler,  and  a  very  small  portion  escaping 
by  radiation  through  the  walls  of  the  furnace  (if  it  is  not  enclosed 
in  the  boiler  itself,  as  in  internally  fired  boilers),  the  remainder 
of  the  heat  passes  out  of  the  furnace  in  the  heated  gases  of  combus- 
tion. These  give  up  to  the  boiler  a  portion  of  their  heat  as  they  pass 
along  the  heating  surfaces,  and  carry  what  remains  into  the  flue  lead- 
ing to  the  economizer  or  to  the  chimney,  as  the  case  may  be.  How 
much  of  this  heat  shall  be  absorbed  by  the  boiler  and  how  much  shall 
pass  into  the  chimney  depends  upon  a  number  of  variable  conditions 
which  will  be  discussed  later. 

Efficiency  of  the  Heating  Surface. — The  two  principal  sources  of 
loss  of  heat  in  the  ordinary  operation  of  a  steam-boiler  are :  1.  The  loss 
due  to  imperfect  combustion ;  2.  The  loss  of  heat  in  the  chimney-gases. 

If  H j_  represents  the  heat-units  in  1  Ib.  of  the  gases  of  combustion 
in  the  furnace,  and  H2  the  heat-units  in  the  same  quantity  of  the  same 
gases  as  they  leave  the  boiler,  the  efficiency  of  the  heating  surface 
is  represented  by  the  equation 

J-'--  • <« 


PRINCIPLES  AND  DEFINITIONS.  15 

If  7\  represents  the  temperature  of  the  gases  in  the  furnace,  and 

T2  their  temperature  as  they  leave  the  boiler,  the  efficiency  is  also 
represented  by  the  equation 


» 


on  the  asumption  that  the  specific  heat  of  the  gases  is  the  same  at 
each  of  the  two  temperatures.  In  these  equations  H19  H2,  Tlf  and  T2 
are  taken  as  measured  from  the  temperature  of  the  air  supplied  to 
the  furnace. 

From  equation  (2)  we  learn  that  the  efficiency  of  the  heating  sur- 
face may  be  increased  either  by  increasing  2\  or  by  decreasing  T2  or 
by  both.  Therefore  high  efficiency  depends  both  on  high  furnace 
temperature  and  on  low  chimney  temperature.  How  to  increase  the 
furnace  temperature,  and  how,  with  increased  furnace  temperature,  to 
decrease  the  chimney  temperature,  are  the  principal  things  to  be 
learned  in  regard  to  the  fuel  economy  of  steam-boilers. 

The  efficiency  of  the  heating  surface  corresponding  to  different 
temperatures  7\  and  T2  is  shown  in  the  following  table  : 

Tt  =  2500°         2000°         1500°         1000° 

•  -  Efficiency,  per  cent.  -  • 

T2  =  300°  ..........  88  85  80  70 

400°  ..........  84  80  73.3  60 

500°  ..........  80  75  66.7  50 

600°  ..........  76  70  60  40 

700°  ..........  72  65  53.3  30 

800°  ..........  68  60  46.7  20 

900°  .......  ...  64  55  40  10 

1000°  ..........  60  50  33.3  0 

The  highest  figure  of  efficiency  in  the  above  table,  88%,  it  is  scarcely 
possible  to  realize  in  practice  except  under  unusual  conditions,  such  as 
the  supplying  of  the  furnace  with  hot  air  heated  by  the  utilization  of 
some  of  the  heat  of  the  escaping  chimney-gases.  The  lowest  figure, 
0%,  represents  an  impossible  condition,  that  of  no  transfer  of  heat 
from  the  gases  into  the  boiler. 

The  efficiency  commonly  obtained  in  practice  in  the  Western  States 
with  bituminous  coals  burned  in  ordinary  furnaces  is  not  over  60  per 
cent,  and  is  often  less  than  50  per  cent.  Probably  55  per  cent  is  a  fair 
average.  The  highest  efficiency  obtainable  under  the  best  conditions, 
with  mechanical  stokers  and  with  furnaces  adapted  to  burn  the  volatile 
matter  of  the  coal,  is  about  80  per  cent.  The  difference,  25  per  cent 


16  STEAM-BOILER  ECONOMY. 

-r-  80  per  cent  =31.2  per  cent,  is  the  margin  for  saving.  If  only 
half  of  this  saving,  or  15.6  per  cent,  can  be  made,  and  this  is 
easily  possible  by  the  introduction  of  improved  methods  of  burning 
Western  coals,  the  reduction  of  the  cost  of  coal  used  for  steam  pur- 
poses, were  these  improvements  generally  adopted,  would  amount  to 
many  millions  of  dollars  a  year.  This  is  the  most  important  improve- 
ment that  can  be  made  in  existing  American  boiler  practice. 

The  principles  briefly  outlined  in  this  chapter  form  the  basis  of  the 
theory  of  the  economy  of  fuel  in  steam-boilers.  They  will  all  be 
considered  in  greater  detail,  with  reference  to  experimental  data,  in 
succeeding  chapters. 


CHAPTER  II. 
FUEL    AND   COMBUSTION. 

Chemistry  of  Fuel  and  of  Combustion. — The  four  principal  chem- 
ical elements  found  in  fuel  and  in  the  air  used  for  its  combustion  are 
carbon,  hydrogen,  oxygen,  and  nitrogen.  The  chemical  symbols  and 
the  atomic  weights  of  these  four  elements  are  respectively  C, 12; H,  1; 
0,  16;  N,  14.  The  atomic  weights,  or  combining  numbers,  are  the 
relative  proportions  by  weight  in  which  the  elements  always  combine 
with  each  other  to  form  definite  chemical  compounds.  Some  of  these 
compounds  are  the  following: 

Parts  by  Weight. 

Water,  H2O 2H  +  160  =  18H20 

Carbon  monoxide,  CO 12C  +  160  =  28CO 

Carbon  dioxide,  CO2 12C  -f  32O  =  44CO2 

Methane,  CH4 12C  +    4H  =  10CH4 

The  names  of  the  last  three  compounds  are  those  used  in  modern 
works  on  chemistry.  Their  older  names  are:  CO,  carbonic  oxide; 
C02,  carbonic  acid;  CH4,  marsh-gas,  or  light  carburetted  hydrogen. 

Air  is  not  a  chemical  compound,  but  a  mixture  of  oxygen  and 
nitrogen. 

Water-gas  (pure),  2H  +  CO,  is  a  mixture  of  two  parts  hydrogen 
and  28'  parts  carbon  monoxide. 

Carbon  is  found  in  the  pure  and  solid  state  in  the  diamond,  in 
charcoal,  and  in  graphite.  Combined  with  hydrogen  it  is  found  in 
various  oils,  tars,  and  gases.  Combined  with  hydrogen  and  oxygen  it 
is  found  in  the  whole  range  of  vegetable  products.  It  is  the  principal 
constituent  of  coal  and  of  most  other  fuels,  whether  solid,  liquid,  or 
gaseous. 

Hydrogen  is  a  very  light  combustible  gas,  of  only  about  TJT  of 
the  density  of  air.  It  may  be  produced  in  its  pure  gaseous  state  by 
the  electrical  or  chemical  decomposition  of  water.  It  is  also  formed, 
mixed  with  carbon  monoxide,  when  steam  is  passed  through  a  body  of 
white-hot  carbon,  the  chemical  reaction  being  thus  expressed: 

17 


18  STEAM-BOILER  ECONOMY. 

H20  +  C  =  2H  +  CO. 

2  +  16  +  12  =  2  +  28  parts  by  weight. 

18  parts  steam  +  12  parts  carbon  =  30  parts  water  gas. 

Hydrogen  is  a  constituent  of  most  fuels,  solid,  liquid,  and  gaseous, 
combined  either  with  carbon  or  with  both  carbon  and  oxygen  in 
various  proportions. 

Oxygen  is  an  invisible  gas,  16  times  as  heavy  as  hydrogen.  It  is 
found  in  the  gaseous  state,  mixed  with  nitrogen,  in  air.  Combined 
with  -J  of  its  weight  of  hydrogen  it  forms  water.  It  is  the  universal 
supporter  of  combustion,  and  is  the  active  agent  of  corrosion  or  rust- 
ing, forming  oxides  of  the  metals.  It  is  found  combined  with  hydro- 
gen and  carbon  in  wood  and  other  vegetable  products,  forming  about 
40  per  cent  of  the  weight  of  dry  wood;  and  it  is  found  in  coal  in 
proportions  varying  from  2  per  cent  or  less  in  anthracite  to  over  25 
per  cent  in  some  lignites. 

Nitrogen  is  also  an  invisible  gas,  14  times  as  heavy  as  hydrogen. 
It  has  so  little  chemical  affinity  for  other  substances  that  it  cannot 
easily  be  combined  with  them  by  ordinary  chemical  methods.  The 
fixation  of  the  nitrogen  of  the  air,  or  causing  it  to  combine  with 
alkalies  to  form  fertilizers,  is  one  of  the  most  important  problems  of  the 
chemist.  It  is  the  diluent  of  oxygen  in  air,  restraining  its  activity, 
and  causing  combustion  and  corrosion  to  be  less  rapid  than  if  they 
were  effected  in  pure  oxygen.  It  is  one  of  the  chief  causes  of  loss  of 
heat  in  the  operation  of  steam-boilers,  since  it  enters  the  furnace  at 
the  temperature  of  the  atmosphere  and  escapes  in  the  chimney-gases 
at  a  high  temperature.  It  is  found  in  all  coals,  usually  to  the  extent 
of  from  0.5  to  2  per  cent  of  their  weight.  When  coal  is  distilled  this 
nitrogen  appears  in  the  vapors,  combined  with  hydrogen,  as  ammonia, 
NH3,  and  when  the  coal  is  burned  the  NH3  is  decomposed  and  part 
of  the  N  is  oxidized  to  nitric  acid,  HX03. 

Sulphur  is  found  in  most  coals,  in  amounts  ranging  from  0.5  per 
cent  to  ocasionally  5  per  cent  or  more  in  some  poor  coals.  It  is 
contained  in  them  usually  as  iron  pyrites  (sulphide  of  iron),  but 
sometimes  as  sulphate  of  lime.  It  is  always  an  objectionable  constitu- 
ent of  coal,  since  it  causes  the  formation  of  clinker  by  the  fusion  of  the 
ash.  It  has  a  slight  value  as  fuel  when  in  the  form  of  sulphide  of 
iron,  1  Ib.  of  sulphur  in  that  form  having  a  heating  value  about  equal 
to  that  of  Mlb.  of  carbon.  In  the  form  of  sulphate  of  lime  it  has  no 
heating  value. 


FUEL  AND  COMBUSTION. 


19 


Properties  of  Air. — Pure  dry  air  is  composed  of  a"  mixture  of 

;     20.91  parts  0  and  79.09  parts  N  by  volume, 

or  23.15  parts  0  and  76.85  parts  N  by  weight. 

The  figure  20.91  is  the  average  result  of  several  determinations  of 

oxygen  in  air,  given  in  Hempel's  Gas  Analysis.     The  parts  by  weight 

are  calculated  from  this  figure,  using  15.963  and  14.012  as  the  relative 

density,  respectively,  of  oxygen  and  nitrogen,  referred  to  hydrogen  as 

1.     (Air  also  contains  about  1  per  cent,  by  volume,  of  argon,  but  it  is 

not  taken  account  of  in  ordinary  gas  analysis,  being  included  with  the 

nitrogen.) 

The  proportions  usually  given  in  text-books  are :  by  volume,  21  0, 
79  N";  and  by  weight,  23  0,  77  N". 

The  proportion  of  nitrogen  to  oxygen  by  weight  is  76.85-^-23.15 
=  3.320;  by  volume,  79.09  —  20.91  =  3.782. 

The  proportion  of  air  to  oxygen  by  weight  is  100  -=-  23.15  =  4.320; 
by  volume,  100  ~-  20.91  ==  4.782. 

Ordinary  atmospheric  air,  outdoors,  contains  about  4  parts  in 
10,000  of  carbon  dioxide,  and  a  quantity  of  vapor  of  water  depending 
upon  the  temperature  and  the  relative  humidity  of  the  atmosphere. 
The  relative  humidity  is  the  percentage  of  moisture  contained  in  the 
air  as  compared  with  the  amount  it  is  capable  of  holding  at  the  same 
temperature;  it  is  determined  by  the  use  of  the  dry-  and  wet-bulb 
thermometer.  The  degree  of  saturation  for  different  readings  of  the 
thermometer  is  given  in  the  following  tables,  condensed  from  the 
Hygrometric  Tables  of  the  U.  S.  Weather  Bureau. 

RELATIVE    HUMIDITY,    PER    CENT. 


S3 

Difference  between  the  Dry  and  Wet  Thermometers,  Deg.  F. 

li 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

26 

28 

30 

H 

Relative  Humidity,  Saturation  being  100. 

Q 

32 

89 

79 

69 

59 

49 

39 

30 

20 

11 

2 

40 

92 

83 

75 

68 

00 

52 

45 

37 

29 

23 

15 

7 

0 

50 

93 

87 

80 

74 

67 

61 

55 

49 

43 

38 

32 

27 

21 

16 

11 

5 

0 

60 

94 

89 

83 

78 

73 

68 

63 

58 

53 

48 

43 

39 

34 

30 

26 

21 

17 

13 

9 

5 

1 

70 

95 

90 

86 

81 

77 

72 

OS 

64 

59 

55 

51 

48 

44 

40 

30 

33 

29 

25 

22 

19 

15 

12 

9 

6 

80 

96 

91 

87 

83 

79 

75 

72 

68 

64 

01 

57 

54 

50 

47 

44 

41 

38 

35 

32 

29 

26 

23 

20 

18 

12 

7 

90 

96 

9? 

89 

85 

81 

78 

74 

71 

OX 

05 

01 

58 

55 

52 

49 

47 

44 

41 

39 

30 

34 

31 

29 

20 

22 

17 

13 

100 

96 

93 

8Q 

86 

83 

80 

77 

73 

70 

08 

05 

02 

59 

56 

54 

51 

4!) 

40 

44 

41 

39 

57 

35 

33 

28 

24 

21 

110 

97 

93 

90 

87 

84 

81 

78 

75 

73 

70 

07 

05 

02 

60 

57 

55 

52 

50 

48 

46 

44 

42 

40 

38 

34 

30 

20 

120 

97 

94 

91 

88 

85 

82 

80 

77 

74 

72 

09 

67 

65 

02 

CO 

58 

55 

53 

51 

49 

47 

45 

43 

41 

:-'S 

34 

31 

J40 

97 

95 

92 

89 

87 

84 

82 

79 

77 

75 

73 

70 

68 

66 

64 

02 

00 

58 

56 

54 

53 

51 

49 

4V 

44 

41 

38 

20 


STEAM-BOILER  ECONOMY. 


WEIGHTS  IN  POUNDS,  OF  PURE  DRY  AIR,  WATER  VAPOR,  AND  SATURATED  MIXTURES 
OF  AIR  AND  WATER  VAPOR  AT  VARIOUS  TEMPERATURES,  AT  ATMOSPHERIC 
PRESSURE,  29.921  INCHES  OF  MERCURY  OR  14.6963  POUNDS  PER  SQUARE  INCH. 
ALSO  THE  ELASTIC  FORCE  OR  PRESSURE  OF  THE  AIR  AND  VAPOR  PRESENT  IN 
SATURATED  MIXTURES. 

(Copyright,  1908,  by  H.  M.  Prevost  Murphy.) 


Saturated  Mixtures  of  Air  and  Water  Vapor. 

ill 

*k 

1    " 

o     S1""1  b 

«ti| 

iiii 

.fei- 

4* 

A 

II  | 

f^t 

||og 

FilS 

^  08  -iJ  **  3  *" 

1H:°! 

1-li 

111° 

KSQ 

£UQ 

So£S 

Woacco 

£>£2o£ 

£«£i 

H°°s 

££%£ 

0° 

0.086354 

0.0439 

29.877 

0.000077 

0.086226 

0.086303 

0.000898 

12 

0.084154 

0.0754 

29.846 

0.000130 

0.083943 

0.084073 

0.001548 

22 

0.082405 

0.1172 

29.804 

0.000198 

0.082083 

0.082281 

0.002413 

32 

0.080728 

0.1811 

29.740 

0.000300 

0.080239 

0.080539 

0.003744 

42 

0.079117 

0.2673 

29.654 

0.000435 

0.078411 

0.078846 

0.005554 

52 

0.077569 

0.3883 

29.533 

0.000621 

0.076563 

0.077184 

0.008116 

62 

0.076081 

0.5559 

29.365 

0.000874 

0.074667 

0.075541 

0.011709 

72 

0.074649 

0.7846 

29.136 

0.001213 

0.072690 

0.073903 

0.016691 

82 

0.073270 

1.092 

28.829 

0.001661 

0.070595 

0.072256 

0  023526 

92 

0.071940 

1.501 

28.420 

0.002247 

0.068331 

0.070578 

0.032877 

102 

0.070658 

2.036 

27.885 

0.002999 

0.065850 

0.068849 

0.045546 

112 

0.069421 

2.731 

27.190 

0.003962 

0.063085 

0.067047 

0.062806 

122 

0.068227 

3.621 

26.300 

0.005175 

0.059970 

0.065145 

0.086285 

132 

0.067073 

4.750 

25.171 

0.006689 

0.056425 

0.063114 

0.118548 

142 

0.065957 

6.167 

23.754 

0.008562 

0.052363 

0.060925 

0.163508 

152 

0.064878 

7.929 

21.992 

0.010854 

0.047686 

0.058540 

0.227609 

162 

0.063834 

10.097 

19.824 

0.013636 

0.042293 

0.055929 

0.322407 

172 

0.062822 

12.749 

17.172 

0.016987 

0.036055 

0.053042 

0.471146 

182 

0.061843 

15.965 

13.956 

0.021000 

0.028845 

0.049845 

0.728012 

192 

0.060893 

19.826 

10.095 

0.025746 

0.020545 

0.046291 

1.25319 

202 

0.059972 

24.442 

5.479 

0.031354 

0.010982 

0.042336 

2.85507 

212 

0.  059079 

29.921 

0.000 

0.037922 

0.000000 

0.037922 

Infinite 

OXYGEN   AND   AIR   REQUIRED    FOR   THE   COMBUSTION   OF   CARBON, 
HYDROGEN,    ETC. 


Chemical  Reaction. 

Lbs.  O. 
per  Ib. 
fuel. 

Lbs.  N  = 
3.22  XO. 

Air  per 
Ib.  = 
4.32XO. 

Gaseous 
product 
per  Ib.- 

Carbon  to  CO2  
Carbon  to  CO  

C+2O=CO2 

c+o=co 

2^ 
1U 

8.85 
4.43 

11.52 
5.76 

12.52 
6.76 

Carbon     monoxide     to 
CO2 

CO+O  =  CQ2 

V7 

1  90 

2  47 

3  47 

Hydrogen  to  H2O 

2H+O  =  H2O 

8 

26  56 

34.56 

35  56 

Methane,   CH4  to  CO2 
and  H2O  .    . 

CH4  +  4O  =  CO2  +  2H2O 

4 

13  .  28 

17.28 

18.28 

Sulphur  to  SO2  

S+2O=SO2 

1 

3.32 

4.32 

5.32 

FUEL  AND  COMBUSTION. 


21 


DENSITIES    OF    GASES. 


Name. 

Symbol. 

Specific 
Gravity. 
Air=l. 

Wt.  of 
1  litre. 
Grams. 

Wt.  of 
1  cu.  ft. 
Lb. 

Relative 
Density. 
H-l. 

Do.,  ap- 
proximate 
figures. 

Oxygen  .  .  . 

o 

1  10521 

1    43003 

0  088843 

15  96 

—  16 

Nitrogen  
Hydrogen  

N 
H 

0.9701 
0.069234 

1.25523 
0  089582 

0.078314 
0  005589 

14.01 
1 

=  14 
—   i 

Carbon  dioxide.  .  . 
Carbon  monoxide. 
Methane 

C02 
CO 
CH4 

1.51968 
0.96709 
0  55297 

1.96633 
1.25133 
0  71549 

0.122681 
0.078071 
0  044640 

21.95 
13.97 

7  99 

=  22 
=  14 

-   g 

Ethylene  
Acetylene  
Sulphur  dioxide  .  . 
Air  

C2H4 
C2H2 

SO2 

0.96744 
0.89820 
2.21295 
1 

1.25178 
1.16219 
2.86336 
1.2939 

0.078100 
0.73010 
0.178646 
0  .  080728 

13.97 
12.97 
31.96 
14  41 

=  14 
=  13 
=  32 

The  first  two  columns  of  figures  are  from  Hem  pel's  Gas  Analysis,  credited 
therein  to  Landolt  and  Bornstein's  Physickalisch-chemische  Tabellen.  The  litre 
weights  are  referred  to  Berlin.  The  weights  per  cubic  foot  are  based  on  the 
weight  of  air  given  by  Rankine,  0.080728  Ib.  per  cu.  ft.  at  32°  F.  and  atmospheric 
pressure,  and  the  figures  in  the  column  of  specific  gravities. 

Heating  Values  of  Various  Substances. — The  following  table  gives 
the  heating  values  of  different  pure  fuels,  as  determined  by  burning 
them  in  oxygen  in  a  calorimeter: 

HEAT   OF    COMBUSTION    OF    VARIOUS    SUBSTANCES    IN    OXYGEN. 


Heat-units. 

Authority. 

Cent. 

Fahr. 

Hydrogen  to  liquid  water. 

/  34,462 
1  34,342 
/    8,080 
\    8,137 
7,859 
7,861 
7,901 
2,473 
/    2,403 
\    2,385 
5,607 
13,120 
13,063 
11,858 
11,957 
10,102 
9,915 
10,109 
2,250 

62,032 
61,816 
14,544 
14,647 
14,146 
14,150 
14,222 
4,451 
4,325 
4,293 
10,093 
23,616 
23,513 
21,344 
21,523 
18,184 
17,847 
18,196 
4,050 

Favre  and  Silbermann. 
Thomsen. 
Favre  and  Silbermann. 

Berthelot. 

<  t 

1  1 

Favre  and  Silbermann. 

<  <                     <  < 

Thomsen. 
Favre  and  Silbermann. 
Thomsen. 

Favre  and  Silbermann. 

<  i                     <  < 

Thomsen. 

<  < 

Favre  and  Silbermann. 
Calculated. 
N.  W.  Lord.* 

Carbon  (wood  charcoal)  to  carbon 
dioxide,  CO2  
Carbon,  diamond  to  CO2  

black  diamond  to  CO2  
'  '       graphite  to  CO2  
Carbon  to  carbon  monoxide,  CO  .  . 

CO  to  CO2  per  unit  of  CO 

CO  to  CO2  per  unit  of  C  =2^  X  2403 
Methane  (marsh-gas),  CH4  to  CO2 
and  H2O                           

Ethylene   (olefiant  gas),   C2H4  to 
CO2  and  H2O            

Benzole  gas,  C6H6  to  CO2  and  H2O. 

Acetylene,  C2H2  to  CO2  and  H2O  .  . 
Sulphur  to  SO2 

*  See  Appendix  to  this  chapter,  Heating  Value  of  Sulphur  in  Coal,  p.  39. 

The  heating  value  of  methane,  CH4,  if  calculated  according  to  its  composition 
by  the  formula  8080C+34,462H,   using  Favre  and  Silbermann's  figures,   is 


22  STEAM-BOILER  ECONOMY. 

14,675  Centigrade  heat-units,  instead  of  13,063,  the  value  determined  by  a 
calorimeter,  a  difference  of  1612  heat-units.  The  calculated  heating  value  of 
ethylene,  C2H4,  is  11,849,  and  that  of  benzole  gas,  C4H4,  is  10,109  heat-units, 
differing  respectively  from  the  calorimetric  values  only  9  and  7  heat-units. 

In  calculations  of  the  heating  value  of  mixed  fuels  the  value  for 
carbon  is  commonly  taken  at  14,600  British  thermal  units,  which  is 
approximately  the  average  of  the  figures  given  by  Favre  and  Silber- 
mann  and  by  Berthelot,  and  that  of  hydrogen  at  62,000,  which  is 
nearly  the  average  of  the  figures  of  Favre  and  Silbermann  and  of 
Thomsen. 

Taking  the  heating  value  of  C  burned  to  C02  at  14,600  B.T.U., 
and  that  of  C  to  CO  at  4450,  the  difference,  10,150  B.T.U.,  is  the  heat 
lost  by  the  imperfect  combustion  of  each  pound  of  carbon  burned  to 
CO  instead  of  C02.  If  the  CO  formed  by  this  imperfect  combustion 
is  afterwards  burned  to  C02,  the  lost  heat  is  regained. 

Imperfect  combustion,  burning  C  to  CO,  is  caused  by  a  deficient 
air-supply,  which  is  usually  due  to  a  great  thickness  of  fire-bed  rela- 
tively to  the  force  of  the  draft.  With  a  thick  bed  of  hot  coal  upon 
a  grate,  the  carbon  in  the  lower  layer,  where  the  air  supply  is  ample, 
is  burned  to  C02,  and  this  gas  passing  through  the  upper  layers, 
where  the  air  is  lacking,  is,  if  the  temperature  is  sufficiently  high, 
converted  more  or  less  into  CO,  as  in  the  operation  of  a  gas-producer. 
Complete  conversion  requires  a  thick  bed  of  fuel  at  a  high  tempera- 
ture, above  1500°  F. 

Heat  Absorbed  by  Decomposition. — By  the  decomposition  of  a 
chemical  compound  as  much  heat  is  absorbed  or  rendered  latent  as 
was  evolved  when  the  compound  was  formed.  If  1  Ib.  C.  is  burned  to 
C02,  generating  14,600  B.T.U.,  and  the  CO,  thus  formed  is  immedi- 
ately reduced  to  CO  by  passing  it  through  a  body  of  glowing  carbon, 
by  the  reaction  CO.,  +  C  =  2CO,  the  result  is  the  same  as  if  the 
2  Ibs.  C.  had  been  originally  burned  to  2CO,  generating  2  X  4450  = 
8900  B.T.U.  The  2  Ibs.  C.  burned  to  C02  would  generate  2  X  14,600 
=  29,200  B.T.U.,  the  difference,  29,200  —  8900  =  20,300  B.T.U. 
being  absorbed  or  rendered  latent  in  the  2CO,  or  10,150  B.T.U.  for 
each  pound  of  carbon. 

In  like  manner  if  9  Ibs.  of  water  (which  might  be  formed  by  burn- 
ing 1  Ib.  H  with  the  generation  of  62,000  B.T.U.  and  cooling  the 
resulting  H20  to  the  atmospheric  temperature)  be  injected  into  a 
large  bed  of  glowing  coal,  it  will  be  decomposed  into  1  Ib.  H  and  8 
Ibs.  0.  The  decomposition  will  absorb  62,000  B.T.U.,  cooling  the 


FUEL  AND  COMBUSTION.  23 

bed  of  coal  this  amount,  and  the  same  quantity  of  heat  will  again  be 
evolved  if  the  H  is  subsequently  burned  with  a  fresh  supply  of  0.  The 
8  Ibs.  0  will  enter  into  combination  with  6  Ibs.  C,  forming  14  Ibs. 
CO  (since  CO  is  composed  of  12  parts  C  to  16  parts  0),  generating 
6  X  4450  =  26,700  B.T.U.,  and  6  X  10,150  =  60,900  B.T.U.  will 
be  latent  in  this  14  Ibs.  CO,  to  be  evolved  later  if  it  is  burned 
to  C02  with  an  additional  supply  of  8  Ibs.  0. 

Heating  Value  of  Compound  or  Mixed  Fuels.  —  It  is  customary  to 
consider  the  heating  value  of  a  compound  or  mixed  fuel  as  being  equal 
to  the  sum  of  the  heating,  values  of  its  elementary  constituents,  and 
to  calculate  it  by  means  of  Dulong's  formula,  which  is,  using  approxi- 
mate figures,  in  British  thermal  units, 


Heating  value  =  -^14,6000  +  62,OOO^H  -  ^  +  4050sl  ; 
or,    Heating  value  =  ~[si40C  +  34,400  ^H  -  Q\  +  2250sl  , 


in  Centigrade  units,  in  which  C,  H,  0,  and  S  are  respectively  the 
percentages  of  carbon,  hydrogen,  oxygen,  and  sulphur  contained  in  the 
fuel.  The  term  H  —  £0  is  called  the  "available"  or  "disposable" 
hydrogen,  or  that  which  is  not  combined  with  oxygen  in  the  fuel. 

This  formula  does  not  apply  in  the  case  of  a  mixed  gaseous  fuel 
containing  carbon  monoxide,  since,  as  shown  in  the  table  given  above, 
1  Ib.  C  in  the  form  of  CO  generates  when  burning  to  C02  only 
.10,093  B.T.U.  instead  of  14,544  B.T.U.  (Favre  and  Silbermann's 
values),  the  difference,  4451  B.T.U.,  having  already  been  generated 
when  the  CO  was  formed.  The  formula  also  does  not  appear  to  hold 
true  in  the  case  of  some  hydrocarbon  gaseous  fuels,  as  in  the  case  of 
methane,  mentioned  in  the  note  under  the  table,  while  on  the  other 
hand  it  does  appear  to  hold  in  the  case  of  ethylene  and  benzole. 

For  all  the  common  varieties  of  coal,  cannel-coal  and  some  lignites 
being  excepted,  it  is  accurate  within  the  limits  of  error  of  chemical 
analyses  and  calorimetric  determinations,  as  is  shown  by  the  recent 
experiments  of  Mahler  and  of  Lord  and  Haas,  which  are  discussed 
elsewhere  in  this  volume. 

"Available  Heating  Value"  of  Hydrogen.  —  Some  writers  in  giving 
the  heating  value  of  hydrogen  subtract  from  its  total  calorimetric 
value,  62,000  B.T.U.  (found  by  burning  the  gas  in  a  calorimeter  in 
which  the  steam  generated  by  the  combustion  is  condensed  and  cooled 
to  the  temperature  of  the  water  in  the  calorimeter),  a  quantity  rep- 


24  STEAM-BOILER  ECONOMY. 

resenting  the  latent  heat  of  the  steam  generated,  viz.,  970.4  B.T.U. 
per  Ib.  steam,  or  9  X  970.4  =  8733.6  B.T.U.  per  Ib.  hydrogen,  making 
the  net  heating  value  of  hydrogen  "burned  to  steam  at  212°  "  62,000 
-  8734  =  53,266  B.T.U.  per  Ib.  Others  subtract  also  an  additional 
quantity  representing  the  difference  between  the  heat  in  the  9  Ibs.  of 
water  condensed  from  the  steam  at  212°  and  that  in  the  same  water 
when  cooled  down  to  a  given  standard  temperature,  such  as  62°.  This 
difference  is  149. 9  B.T.U.  perlb.  water,  or9  x!49.9  =  1349.1  B.T.U. 
per  Ib.  hydrogen,  which  subtracted  from  53,266  gives  51,917  B.T.U. 
as  the  available  heating  value  of  1  Ib.  hydrogen  burned  with  8  Ibs. 
oxygen,  both  gases  being  supplied  at  62°,  and  the  product,  9  Ibs  H20, 
escaping  as  steam  at  212°. 

This  use  of  heating  values  of  hydrogen  "  burned  to  steam,"  in 
computations  relating  to  combustion  of  fuel,  is  inconvenient,  since  it 
necessitates  a  statement  of  the  conditions  upon  which  the  figures  are 
based ;  and  it  is,  moreover,  misleading,  if  not  inaccurate,  since 
hydrogen  in  fuel  is  not  often  burned  in  pure  oxygen,  but  in  air,  the 
temperature  of  the  gases  before  burning  is  not  often  the  assumed 
standard  temperature,  and  the  products  of  combustion  are  rarely  dis- 
charged at  212°.  In  steam-boiler  practice  the  chimney-gases  are 
usually  discharged  at  a  temperature  above  300° ;  but  if  economizers 
are  used,  and  the  water  supplied  to  them  is  cold,  the  gases  may  be 
cooled  to  below  212°,  in  which  case  the  steam  in  the  gases  is  con- 
densed and  its  latent  heat  of  evaporation  is  utilized. 

If  there  is  any  need  at  all  of  using  figures  of  the  "available" 
heating  value  of  hydrogen,  or  of  its  heating  value  when  "burned  to 
steam,"  the  fact  that  the  gas  is  burned  in  air  and  not  in  pure  oxygen 
should  be  taken  into  consideration.  The  resulting  figures  will  then  be 
much  lower  than  those  above  given,  and  they  will  vary  with  different 
conditions,  as  shown  below. 

(1)  Suppose  1  Ib.  H  to  be  burned  in  just  enough  air  to  supply  8 
Ibs.  0,  that  the  H  and  the  air  are  supplied  at  62°,  and  the  products 
of  combustion  escape  at  212°.  We  have: 

Total  heating  value  of  1  Ib.  H 62  000  B.T.U. 

Heat  lost,  latent  heat  of  9  Ibs.  H2O  at  212° . .  =  8734 

9  Ibs.  H2O  heated  from  62°  to  212° =  1349 

Nitrogen  with  8  Ibs.  O  heated  from  62°  to 

212°  =8X3.32X150X0.2438     (specific 

teat) =  971      11,054     " 


Net  available  heating  value 50,946 


FUEL  AND  COMBUSTION.  25 

(2)  Suppose  that  the  air-supply  is  double  that  required  to  effect 
the  combustion  of  the  H,  other  conditions  being  the  same  as  in  (1). 
The  additional  heat  lost  will  be : 

Excess  air  8X4.32  =  34.56  Ibs.X  150X0.2375 =       1,231  B.T.U. 

Which  will  reduce  the  net  heating  value  to 49,715      " 

(3)  Suppose  that  with  the  double  air-supply  tne  products  of  com- 
bustion escape  at  562°.     The  heat  lost  will  then  be  as  below : 

9  Ibs.  water  heated  from  62°  to  212° 1,349  B.T.U. 

Latent  heat  of  9  Ibs.  H2O  at  212° 8,734      ' ' 

Superheated  steam,  9  Ibs.X (562 -212)  X0.48(sp.ht.)*  1,512      " 

Nitrogen,  26.56  X  (562  -62)  X0.2438 3,238      ' ' 

Excess  air,  34.56  X  (562 -62)  X 0.2375 4,104 


Total  losses 18,936      " 

Which  subtracted  from  62,000  gives  41,064  B.T.U.  as  the  net  avail- 
able heating  value. 

It  is  better  in  all  calculations  of  the  heating  value  of  fuel  and  of 
the  results  of  combustion  in  steam-boiler  practice,  to  avoid  the  use  of 
this  so-called  "available  heating  value/'  and  to  take  the  heating  value 
of  hydrogen  (or  that  part  of  the  hydrogen  which  is  not  already  com- 
bined with  oxygen  in  the  fuel)  at  62,000  B.T.U.  The  various  heat 
losses,  calculated  as  above,  which  vary  with  the  conditions,  are  then 
not  subtracted  from  the  heating  value  of  the  fuel,  but  are  taken  as 
losses  of  heat  in  the  chimney-gases. 

In  calculations  of  the  relative  commercial  value  of  different  fuels 
containing  hydrogen  or  water,  however,  account  must  be  taken  of  the 
loss  of  heat  due  to  superheated  steam  escaping  in  the  chimney-gases. 

Available  Heating  Value  of  a  Fuel  containing  Hydrogen, — The 
total  heating  value  of  a  hydrogenous  fuel  being 

14,6000  +  62,000  (H  -  — 

\  C7 

to  find  the  available  heating  value  for  any  assumed  temperature  of  the 
air-supply  and  of  the  chimney-gases,  we  subtract  the  heat  lost  in  the 
superheated  steam  which  escapes  into  the  chimney,  or 

9H  X  [(212°  -  0  +  970.4  +  0.48(7;  -  212°)], 

*  The  specific  heat  of  superheated  steam  at  atmospheric  pressure  is  com- 
monly taken  at  0.48.  Knobloch  and  Jakobs'  experiments  (see  Peabody's  Steam 
Tables)  give  it  at  0.463  at  212°  F.,  0.462  at  302°  and  390°  F.,  rising  to  0.473 
at  752°  F. 


26  STEAM-BOILER  ECONOMY, 

in  which  t  is  the  temperature  of  the  air  supply  and  Tc  that  of  the 
chimney-gases.  This  calculation  takes  no  account  of  the  nitrogen 
which  is  in  the  air  required  to  burn  the  hydrogen,  nor  of  the  excess 
air-supply,  the  loss  of  heat  due  to  these  being  considered  as  part  of  the 
loss  in  the  dry  chimney-gases,  consisting  of  C02,  CO,  0,  and  N". 

EXAMPLE. — What  is  the  total  heating  value  and  the  available  heat- 
ing value  of  1  Ib.  of  combustible  consisting  of  0.91C+ .05H-f-.040, 
the  air  for  combustion  being  supplied  at  62°  and  the  chimney -gases 
escaping  at  562°  ? 

Total  heating  value,  0.9 IX  14,600 +  .045X62,000 =16,076  B.T.U. 

Heat  lost  in  steam,  9 X.05[150 +970 +  (0.48X350)] =      580      " 


Difference,  or  available  heating  value 15,496    ' ' 

The  heat  lost  in  the  steam  is  about  3.5%  of  the  total  heating  value. 

Available  Heating  Value  of  a  Fuel  Containing  Hydrogen  and 
Water. — In  this  case  the  heat  lost  includes,  besides  that  due  to  the 
superheated  steam  formed  by  the  combustion  of  the  available  hydro- 
gen, that  is,  the  hydrogen  of  the  dry  fuel  less  one  eighth  of  the  oxy- 
gen of  the  dry  fuel,  the  heat  due  to  the  superheated  steam  formed 
from  the  water  in  the  fuel,  or 

(9H  +  W)  X  [212  -  0  -+  970  +  0.48(TC  -  212)], 
in  which  W  is  the  water  in  1  Ib.  of  the  fuel. 

EXAMPLE. — What  is  the  available  heating  value  of  1  Ib.  of  moist 
wood  whose  analysis  is  38C,  5H,  320,  1  ash,  24  water,  =  100$,  the 
air  being  supplied  at  62°  F.  and  the  chimney-gas  escaping  at  412°  ? 

Total  heating  value,  38  X  14,600  +  (5  -  4)  X  62,000 =  6168  B.T.U. 

Heat  lost  in  superheated  steam  (9  X  -05  +  0.24) 

X  [150  +  970  +  (0.48  X  200)] =  _839       " 

Available  heating  value =  5329       " 

The  heat  loss  in  the  steam  in  this  case  is  nearly  14%  of  the  total 
heating  value. 

Temperature  of  the  Fire. — Assuming  that  a  pure  fuel,  such  as 
carbon,  is  thoroughly  burned  in  a  furnace,  all  of  the  heat  generated 
will  be  transferred  to  the  gaseous  products  of  combustion,  raising  their 
temperature  above  that  at  which  the  fuel  and  the  oxygen  or  air  are 
supplied  to  the  furnace.  Suppose  that  1  Ib.  C  is  burned  with  2f  Ibs. 
O,  forming  3f  Ibs.  C02,  both  the  C  and  the  0  being  supplied  at  0°  -F. 


FUEL  AND  COMBUSTION.  27 

The  combustion  of  the  1  Ib.  C  generates  14,600  B.T.U.,  which  will 
all  be  contained  in  the  3|  Ibs.  C02.  The  specific  heat  of  C02  is  0.217; 
that  is,  it  requires  0.217  B.T.U.  to  raise  the  temperature  of  1  Ib.  of 
C02  one  degree  Fahrenheit.  To  raise  2|  Ibs.  C02  one  degree  will  re- 
quire 3f  X  0.217  =  0.7957  B.T.U.,  and  14,600  B.T.U.  will  therefore 
raise  its  temperature  14,600  -^0.7957  =  18,350°  F.  above  the  tem- 
perature at  which  the  C  and  the  0  were  supplied.  The  temperatures 
thus  calculated  are  known  as  theoretical  temperatures,  and  are  based 
on  the  assumptions  of  perfect  combustion  and  no  loss  by  radiation. 
The  temperature  of  18,350°  is  far  beyond  any  temperature  known  in 
the  arts,  and  it  is  probable  that  long  before  it  could  be  reached  the 
phenomenon  of  dissociation  would  take  place ;  that  is,  the  C02  would 
be  split  up  into  C  and  0,  and  the  elements  would  lose  their  affinity 
for  -each  other. 

The  theoretical  elevation  of  temperature  of  the  fire  may  conveni- 
ently be  calculated  by  the  formula 

e  ,  B.T.U.  generated  by  the  combustion 

Elevation  of  temp.  =  ^7  .  ,. — j— ^  r—. —      -. . 

Weight  of  gaseous  products  X  their  sp.  heat 

It  is  evident  from  this  formula  that  the  rapidity  of  the  combustion,  or 
the  time  required  to  burn  a  given  weight  of  fuel,  has  nothing  to  do 
with  the  temperature  that  may  theoretically  be  attained.  In  practice 
the  temperature  of  a  bed  of  coal  in  a  furnace  and  that  of  the  burning 
gases  immediately  above  the  coal  are  reduced  to  some  extent  by  radia- 
tion, and  as  the  quantity  of  heat  radiated  from  a  given  mass  of  fuel  is 
a  function  of  the  time  during  which  it  takes  place,  a  considerable  por- 
tion of  the  heat  generated  may  be  lost  by  radiation  when  the  combus- 
tion is  very  slow.  With  ordinary  rates  of  combustion,  however,  say 
10  Ibs.  of  coal  per  sq.  ft.  of  grate  surface  per  hour,  and  fire-brick 
furnaces,  the  percentage  of  loss  of  heat  by  radiation  is  quite  small, 
1%  or  less,  and  the  actual  temperature  that  may  be  attained  will  be 
very  nearly  as  high  with  that  rate  of  combustion  as  with  a  rate  of  20 
or  40  Ibs. 

Maximum  Theoretical  Temperature  due  to  Burning  Carbon  in  Dry 
Air.— 1  Ib.  C  burned  to  C02  generates  14,600  B.T.U.  The  products 
of  combustion  are  3f  Ibs.  C02  +  2f  X  3.32  =  8.853  Ibs.  N  =  12.52 
Ibs.  gas.  Taking  the  specific  heat  of  C02  at  0.217,  and  that  of  N  at 
0.2438,  we  have  for  the  specific  heat  of  the  gas 

(3J  X  0.217  +  8.853  X  0.2438)  -r-  12.52  =-  0.2359. 


STEAM-BOILER  ECOXOMY. 


The  elevation  of  temperature  of  the  fire  above  the  atmospheric  tem- 
perature is  14,600  H-  (12.52  X  0.2359)  =  4942.5°. 

If  the  atmospheric  temperature  is  62°  F.?  then  the  temperature  of 
the  fire  is  4942.5  4-  62  =  5004.5°. 

The  temperatures  found  by  the  above  calculations  can  never  be 
reached  in  practice,  since  it  is  not  possible  to  effect  complete  com- 
bustion without  a  considerable  excess  of  air  above  the  theoretical 
requirement-  The  fact  that  the  specific  heat  of  the  gases  of  com- 
bustion, at  high  temperatures,  is  higher  than  the  figures  given, 
would  also  have  the  effect  of  reducing  the  temperature. 

Taking  the  specific  heat  of  the  gases  at  0.237.  the  figure  commonly 
taken  in  temperature  calculations,  the  calculated  elevation  of  temper- 
ature is  14,000 -T-  (12.52  X  0.23?)  =  4920°  F. 

TEMPERATURE    OF   THE    FIRE,    CAKBOX   BEING    BURXED    PART   TO    CO    AXD 

PART   TO    OOi. 

Heating  value  of  1  Ib.  C  burned  to  CO* 14,600  B.T.U. 

«      .<     «      „       "CO.  4,450       " 


Air  supplv  below  11,52  Ibs..  per  cent 
Air  per  Ib.  C,  Ibs  

0 
11.52 

10 
10.37 

20 
9.22 

30 
8.06 

40 

6  91 

50 
5  76 

Air-t-r=pus_  Ika 

12.52 

11.37 

10.22 

9.06 

7  91 

6  76 

C  burned  to  COj.  per  cent.  .  . 

100 

BO 

60 

40 

20 

0 

C      "       4i  CO,    "      "  

0 

20 

40 

60 

80 

100 

B.T.U.  generated  in  making  CO,..  . 
B.T.U.  generated  in  making  CO.  .  . 
Total  heat  generated 

14.600 
0 
14,600 

11,680 
HM 
12,570 

8,760 
1,780 
10.540 

5.840 
2,670 
8.510  i 

2.920 

o.o-V. 

6,480 

0 
4.450 
4.450 

1am  due  to  CO,  B.T.U  

0 

2,030 

4,060 

6,090 

8.120 

10,150 

Elevation  of  temperature  of  fire 
(taking  specific  heat  of  gases  at  - 
024 

4860° 

4606° 

4298* 

3914= 

3418° 

2743  = 

1  CO*.... 
Gas  analysis  bv  volume  >  CO  
i  N     . 

20.86 
0 
79  14 

18.12 
4  53 
77  35 

14.87 
9  91 
75  22 

10  94  i 
16  41 
72  65 

6  10 
24  42 

69  48 

0 

34  .51 
65  49 

•»-,- 

TEMPERATURE    OF   THE    FIRE,    CARBOX   BURXED   TO    CO*   WITH    EXCESS   OF   AIB. 


Air-supplv  above  11.52  Ibs.  per  cent 
Air  per  Ib.  C,  Ibs.  

25 
14.40 

50 

17.28 

75 

20.16 

100 
23.04 

150 

Ox     xT, 

200 
34.56 

Air-J-C^gas,  Ik* 

15.40 

18.28 

21.16 

24.  04 

29.80 

35.56 

Elevation  of  temperature  of  fire  .  . 
1  CO,.... 
Gas  analysis  bv  volume  -  O  .  . 

3950s 
16  69 
4  17 

3328° 
13.91 
6.95 

2875° 
11.92 
8  94 

2530° 
10  43 
10.43 

2041° 
8  34 
12  52 

1711° 
6  95 
13  91 

N 79  14   79.14   79. 14>  79  14   79  14  79  14 


Theoretical  Temperature  dne  to  Burning  Hydrogen  in 
Dry  Air.— 1  Ib.  H  burned  to  H20  generates  62,000  B.T.U.  The 
products -<>f  combustion  are  9  Ibs.  H20  (superheated  steam)  and 


FUEL  AND  COMBUSTION. 


29 


8  X  3.32  =  26.56  Ibs.  X.  Let  /  =  temperature  of  the  atmosphere 
and  T  -j-  /  =  temperatnre  of  the  products  of  combustion,  0.48  = 
specific  heat  of  superheated  steam,  and  0.2438  =  specific  heat  of 
nitrogen.  Then 

62,000  =  9[(212-/)+970.4+0.48(r+/-212)]  -{-26.56X0.24387". 


212  —  f  is  the  B.T.U.  required  to  heat  1  Ib.  of  water  from  t  to 
970.4  is  the  latent  heat  of  evaporation  at  212°,  and  0.48  (T+t—  212) 
is  the  heat  required  to  heat  1  Ib.  of  steam  from  212s  to  T-j-  f. 


f: 


25 


52  CC 

Air    Supply. 

FIG.  1.  —  MAXIMUM  THEORETICAL  TEMPERATURE  OF  THE  FERE  DUE  TO  BURX- 
IXG  CARBON  WITH  DIFFERENT  QUAXTITIES  OF  ATR. 

Taking  /  at  62°.  we  have 

62,000  =  9[1044.6  -h  0.48  T]  +  6.4757 

=  90401.4  -f-  10.795  T. 
Whence  T=  4872.5,     and     T+t  =  4934.5°  F. 

The  maximum  theoretical  temperature  due  to  burning  hydrogen 
in  air  and  that  due  to  burning  carbon  in  air  are  very  nearly  the  same. 

Temperature  of  the  Fire,  tlie  Fuel  containing  Hydrogen  and 
"Water.  —  The  gaseous  products  of  combustion,  in  this  case  will  contain 


30  STEAM-BOILER  ECONOMY. 

superheated  steam,  formed  from  the  combustion  of  the  hydrogen  in 
the  coal  and  the  evaporation  of  the  moisture.  The  calculation  of  the 
temperature  of  the  fire,  assuming  perfect  combustion  and  no  loss  by 
radiation,  may  be  made  in  the  following  manner.  Reduce  the  analysis 
of  the  fuel  in  percentages  of  C,  H,  0,  and  moisture  to  decimal  parts 
of  1  lb. 

Let  111  =  H  —  \0  =  available  hydrogen  ; 
W  =  moisture  in  the  fuel, 
T  =  elevation  of  the  temperature  of  the  fire  above  the  atmos- 

pheric temperature; 

t  =  temperature  of  the  atmosphere,  say  60°  F.  ; 
L  =  latent  heat  of  evaporation  at  212°  =  970.4; 
a  =  heating  value  of  1  lb.  of  carbon  =  14,600  ; 
&  =  heating  value  of  1  lb.  of  hydrogen  =  62,000  ; 
/  =  Ibs.  of  dry  gas  per  lb.  of  fuel  =  C02  +  N  +  excess  air; 
c  —  specific  heat  of  the  gas  =  0.237  ; 
9£T  —  Ibs.  of  steam  formed  by  burning  the  available  H  ; 
W  +  9H  =  superheated  steam  in  the  gases  ; 

0.48  —  specific  heat  of  superheated  steam. 

The  total  heat  developed  by  burning  1  lb.  of  the  fuel  will  be 
aC  -\-bHi  heat  units. 

All  of  this  heat  will  be  utilized  in  raising  the  temperature  of  the 
gas  and  steam  to  T°  above  the  atmosphere.  The  dry  gas  will  contain 
cfT  heat-units,  and  the  superheated  steam 


(  W+  9#)[212  -  1  +  L  +  OAS(T  +  t  - 
We  have  then 

aC+bHi  =  0.237/T  +  (  W+  9#)[212  -  t  +  L  -f-  0.48(r  +  t  -212)] 
=  [0.237/+0.48(JT+97/)]77+(>r+  9#)(1080.6-  0.52Q. 

Transposing, 


-(W  +  9fl)  (1080.6-0.520 
0.237/+0.48(JF  +  9J5T) 

Substituting  for  a,  £,  and  HI  their  values,  and  taking  t  =  62°, 


14,600C  +  62,000(g-  |0)  -  1048.4(Tf  +  9#) 
0.237/+0.48(JF+9#) 


FUEL  AND  COMBUSTION.  31 

Taking  C,  H,  0,  and  W  in  percentages,  instead  of  in  decimal  parts, 
the  formula  reduces  to  (a  very  close  approximation) 

616C  +  2220#  -  327  0  -  44  W 


EXAMPLES.  —  1.  Given  a  coal  whose  analysis,  excluding  ash  and 
sulphur,  is  75C,  5H,  100,  and  10  moisture,  with  dry  gas=20  Ibs. 
per  Ib.  of  this  combustible,  including  moisture: 

T  -  616  X  75  +  2220  X  5  -  327  X  10  -  44  X  10  _ 
20  +  0.02X10  +  .18X5 
T+t  =  2602°  F. 

The  first  of  the  two  formulse  gives  2600°  F. 

The  sulphur  in  coal  may  be  neglected  in  calculations  of  tempera- 
ture, since  3  per  cent  of  sulphur  would  not  increase  the  temperature 
one  per  cent,  taking  4000  B.T.U.  as  the  heating  value  of  sulphur. 
The  error  due  to  neglecting  it  is  less  than  the  probable  error  of  the  fig- 
ure, 0.237,  for  the  specific  heat  of  furnace-gases  at  high  temperatures. 

2.  Required   the    maximum   temperature    attainable    by   burning 
moist  wood  of  the  composition  C,  38  ;  H,  5  ;  0,  32  ;  ash,  1  ;  moisture, 
24;  the  dry  gas  being  15  Ibs.  per  Ib.  of  wood,  and  temperature  of 
the  atmosphere  62°. 

T      616  X  38  +  2220  X  5  -  327  X  32  -  44  X  24  _ 
15  +  0.02X24  +  0.18X5 

T+t  =  1465°. 

3.  Since  the  carbon  and  the  available  hydrogen  make  only  39%  of 
the  weight  of  the  wood,  a  much  smaller  air-supply  than  that  required 
to  make  15  Ibs.  of  dry  gas  per  Ib.  of  wood  may  be  sufficient  to  effect 
complete  combustion.    If  we  take  the  dry  gas  at  10  Ibs.  instead  of  15, 
the  temperature  T  will  be 

22988 


10  +  1.38 


=  2020°. 


4.  Required  the  theoretical  temperature  of  a  fire  of  Pocahontas 
coal  of  the  following  anaylsis:  C,  84.22;  H,  4.26;  0,  3.48;  N,  0.84; 
S,  0.59;  ash,  5.85;  water,  0.76;  the  dry  gas  being  20  Ibs.  per  Ib.  of 
combustible,  the  heating  value  of  the  S  being  neglected. 


32  STEAM-BOILER  ECONOMY. 

The  combustible,  C,  H,  0,  and  N,  is  92,80%  of  the  coal; 

/  =  20  X  .928  =  18.56. 
616  X  84.22  +  2220  X  4.26  -  327  X  3.48  -  44  X  0.76 


18.56  +  0.02  X  0.76  +  .18  X  4.26 
T  +  t  =  3110  +  62°  =  3172°. 


=  3110°; 


Pure  carbon  burned  with  19  Ibs.  air  per  lb.,  making  20  Ibs.  of  gas, 
by  the  same  formula  gives  T  =  3080,  T  -\- t  =  3142.  The  semi- 
bituminous  coal  therefore  gives  a  trifle  higher  temperature  than  pure 
carbon. 

Actual  Temperature  of  the  Fire  usually  Less  than  the  Theoretical. 
— In  order  to  realize  in  practice  the  temperatures  given  by  the  above 
theoretical  calculations,  it  is  necessary  that  the  air  be  delivered  to  the 
incandescent  fuel  at  a  perfectly  uniform  rate;  that  the  combustion  of 
the  hydrogen  be  complete ;  that  the  combustion  of  the  carbon  be  com- 
plete, forming  C02  when  the  air  supply  equals  or  exceeds  11.52  Ibs. 
per  lb.  of  carbon  burned,  or,  when  the  air-supply  is  less  than  this,  that 
all  of  its  oxygen  be  used  to  form  either  CO  or  C02 ;  and  that  there  be 
no  loss  by  radiation  from  the  incandescent  fuel  into  the  surrounding 
furnace  or  boiler  walls.  These  conditions  can  be  nearly  obtained  under 
some  circumstances,  such,  for  instance,  as  with  gaseous  fuel  with  an 
intimate  and  regular  admixture  of  air,  the  combustion  taking  place  in 
a  chamber  with  thick  fire-brick  walls;  with  dust  fuel  burned  under 
similar  conditions;  and  with  a  thick  fire  of  anthracite,  egg  size, 
burned  in  a  fire-brick  chamber  with  a  steady  draft,  after  the  freshly 
fired  uper  layer  of  coal  has  reached  the  temperature  of  the  furnace. 
With  insufficient  air-supply  the  actual  temperature  is  always  less  than 
the  theoretical,  for  the  reason  that  some  of  the  oxygen  passes  through 
the  fire  without  entering  into  combination  with  carbon.  Generally 
the  air-supply  is  not  regular,  even  with  a  steady  draft  pressure,  for 
the  reason  that  the  freshly  fired  coal  chokes  to  some  degree  the  air- 
passages  through  the  bed,  causing  the  formation  of  some  CO  and 
chilling  the  furnace.  When  the  fire-bed  is  directly  underneath  the 
comparatively  cool  surface  of  the  boiler,  radiation  from  the  bed  re- 
duces the  furnace  temperature. 

The  author  has  obtained  temperatures  exceeding  3000°  F.,  as  meas- 
ured by  a  Uehling  &  Steinbart  recording  pneumatic  pyrometer,  with 
Pittsburg  coal  containing -less  than  2%  of  moisture,  and  having  a  heat- 
ing value  of  15,000  B.T.TJ.  per  lb.  of  dry  combustible.  The  conditions 
were  a  fire-brick  combustion-chamber  and  frequent  firing  of  small 


FUEL  AND  COMBUSTION. 


33 


quantities  of  coal  at  a  time.  This  corresponds  nearly  to  the  theoretical 
temperature  due  to  an  air-supply  of  18  Ibs.  per  Ib.  of  combustible, 
which  is  about  the  figure  found  in  practice  to  give  the  highest 
efficiency  of  steam-boiler  performance. 

Excessive  Carbon  Monoxide  produced  by  Heavy  Firing. — A  series 
of  experiments  by  J.  C.  Hoadley  (Trans.  A.  S.  M.  E.,  vol.  vi.  p.  794), 
in  which  for  three  hours  anthracite  egg  coal  was  fired  on  the  grates  at 
the  rate  of  200  Ibs.  in  each  half-hour,  when  the  rate  at  which  the  coal 
was  burned  was  only  about  140  Ibs.,  thus  steadily  increasing  the  thick- 
ness of  the  bed  of  coal,  showed  the  following  results,  the  gases  being 
analyzed  every  half-hour : 


Half-hour  periods                              .  . 

1 
2.54 
5.12 
33.2 

2 
2.99 
5.55 
29.5 

3 
3.99 
7.79 
21.4 

4 
4.61 
7.70 
20.1 

5 
4.70 
7.82 
19.8 

6* 
4.81 
8.01 
19.3 

7* 
0.25 
15.21 
19.3 

8 
0.21 
14.11 
20.8 

CO  in  gases  per  cent 

CO2  "     "    '  "      " 

Lbs.  air  per  Ib.  coal  

*  Intervals  of  one  hour. 

The  firing  was  at  the  rate  of  200  Ibs.  of  coal  every  half-hour  until 
11.15  A.M.,  or  fifteen  minutes  before  the  sixth  sample  of  gas  was 
taken.  The  next  lot  of  200  Ibs.  coal  was  not  fired  until  12.45  P  M., 
and  no  more  was  fired  until  after  the  eighth  sample  of  gas  was  taken. 
The  seventh  sample  was  taken  at  12.30,  and  the  eighth  at  1.30,  each 
forty-five  minutes  after  firing  2.00  Ibs.  of  coal.  The  results  show  a 
steady  increase  in  CO  up  to  11.30  A.M.,  as  the  bed  of  coal  became 
thicker,  and  a  reduction  to  a  low  figure  when  the  bed  became  thin. 

These  tests  show  that  it  is  sometimes  possible  for  a  high  percentage 
of  CO  and  a  great  excess  of  air-supply  to  exist  at  the  same  time.  This 
may  be  explained  by  supposing  that  the  excess  of  CO  was  generated  at 
one  portion  of  the  grate  surface,  and  that  the  excess  of  air  entered  at 
another — or  else  leaked  into  the  boiler-setting  beyond  the  bridge-wall 
—and  that  the  two  currents,  one  of  CO  and  the  other  of  air,  were 
never  brought  into  contact  until  their  temperature  was  reduced  below 
the  point  of  ignition. 

Calculation  of  the  Weight  of  Air  supplied,  and  the  Weight  of  the 
Gases,  from  the  Analysis  of  the  Gases  by  Volume.* — Given  a  coal  con- 

*  To  convert  analysis  by  volume  into  analysis  by  weight,  multiply  the  per- 
centage of  each  constituent  gas  by  its  relative  density,  viz.,  C02  by  11,  O  by  8, 
CO  and  N  each  by  7,  and  divide  each  product  by  the  sum  of  the  products.  Per 
contra,  to  convert  analysis  by  weight  into  analysis  by  volume,  divide  the  per- 
centage by  weight  of  each  gas  by  its  relative  density,  and  divide  each  quotient 
by  the  sum  of  the  quotients. 


34 


STEAM-BOILER  ECONOMY. 


taining  66C,  5H,  80,  IN,  8  water,  and  12  ash,  ==  100%,  it  is  required 
to  compute  the  analysis,  by  weight  and  by  volume,  of  the  gaseous 
products  of  combustion,  on  the  assumptions  (1)  that  60C  is  burnt 
to  C02  and  6  to  CO ;  (2)  that  the  supply  of  dry  air  is  20%  in  excess  of 
that  required  to  effect  this  combustion  of  the  C  and  to  burn  the  avail- 
able H  (  =  H  —  f  0)  to  H20 ;  and  (3)  that  the  dry  air  is  accompanied 
by  1%  of  its  weight  of  moisture.  It  is  also  required  to  determine  the 
weight  of  dry  air  and  of  dry  gas  per  Ib.  of  carbon  and  per  Ib.  of  fuel, 
and  furthermore  to  find  formulas  by  means  of  which  these  weights 
may  be  computed  directly  from  the  analysis  of  the  gases  by  volume. 

We  first  construct  a  table  in  which  are  shown  the  elements  of  the 
coal  and  of  the  air  which  combine  to  form  the  gaseous  products,  as 
follows : 


Per  cent  or  Parts 
in  100  Lbs.  Fuel. 

O  from 
the  Air. 

N  from  the 
Air=OX3.32 

Total 
Air. 

CO2. 

CO. 

HjO. 

60C  toCO2  X2y3  = 
6C  to  CO   X  1]^  = 
4H  to  HoO  X  8     = 

160 
8 
32 

531.20 

26.56 
106  24 

691  .  20 
34.56 
138  24 

220 

'u 

36 

lr?  \  tO   H2O 

200 

664.00 

864.00 

9 

8O    j 
1  N 

1  00 

8  water 

8 

12  ash 

100 
Excess  air  20% 

40 

132  80 

172  80 

Total  dry  air 

1036  80 

Moisture  in  the  air 

10.4 

Total  gases,  1135.2  = 

40 

797.8 

220 

14 

63.4 

Total  dry  gases  1071.80  or  3 . 732    74 . 436   20 . 526     1 . 306%  by  wt. 

Total  dry  gases  %  by  vol.  3.547     80.847   14.187     1.419 

Total  gas  1135.2+12  ash  =  100  coal  +  1036.80  air  +  10.4  moisture  in  air. 

Dry  gas  per  Ib.  coal  10.718  Ibs.;  per  Ib.  C  =  1071. 8 -^66  =  16. 239  Ibs. 

Dry  air  per  Ib.  coal  10.368  Ibs.;  per  Ib.  C  =  1036. 8-^66  =  15. 709  Ibs. 

The  air  and  gas  per  Ib.  coal  and  per  Ib.  C  may  be  calculated  from 
the  analysis  of  the  gases  by  weight  or  by  volume,  as  follows : 

Let  CO2  +  O  +  CO  +  N  =  total  gas,  in  percentages,  by  weight. 
The  carbon  in  the  CO2  =  T3iCO2,  and  that  in  the  CO  =  fCO.  This 
carbon  was  supplied  by  the  fuel.  We  then  have 

CO2  +  O  +  CO  +  N  100 


Dry  gas  per  Ib.  C  = 


i8TC02  +  f  CO 


AC0 


FUEL  AND  COMBUSTION.  35 

Multiplying  the  result  by  the  C  in  1  Ib.  coal  gives  the  dry  gas  per  Ib. 
of  coal. 

Multiplying  each  term  in  this  formula  by  the  respective  figures 
for  relative  density  of  the  several  gases,  viz.,  C02,  11;  0,  8;  CO  and 
N,  7,  we  obtain 


in  which  C02,  0,  CO,  and  N  are  percentages  by  volume.    Taking  the 
percentage  by  volume  given  in  the  above  table,  we  have 

11  X  14.187  +  8  X  3.547  +  7  X  82.266 
Drygasperlb.C  3(14.187  +  1.419) 

=  16.239  Ibs.,  as  before. 
Dry  gas  per  Ib.  coal  =  16.239  X  .66  =  10.718  Ibs.      ' 

Th  7N  in  the  la.st  formula  represents  the  N  supplied  by  the  air, 
plus  the  relatively  insignificant  amount  of  about  1  part  in  800  fur- 
nished by  the  coal,  as  shown  in  the  table.  As  the  N  supplied  by  the  air 
is  76.85%,  or  3.32-1-4.32,  of  the  weight  of  the  air,  we  have 


7(N  -  gfoN)       432         3.032N 
Dry  air  per  Ib.  C   =  X 


in  which  C02,  CO,  and  N  are  percentages  by  volume  of  the  dry  gas. 

This  last  formula  is  a  most  useful  one  for  computing  the  air- 
supply  per  Ib.  C  from  the  analysis  of  the  gases  by  volume.  Substitut- 
ing the  percentages  found  in  the  example,  we  have 

1U  n      3.032  X  80.847  7n7  „ 

Dry  air  per  Ib.  C    -  14  187  +  -  15-707  Ib., 


which  is  practically  the  same  as  the  result  obtained  from  the  table. 

Excess  of  Air-supply  above  the  Theoretical  Minimum  Require- 
ment. —  Referring  to  the  table  of  computations  in  the  above  example, 
p.  34,  it  will  be  seen  that  all  the  nitrogen  in  the  gases,  80.847%  by 
volume,  came  from  the  total  air-supply,  except  an  insignificant 
amount  furnished  by  the  coal.  The  oxygen,  3.547%,  all  came  from 
the  excess  air-supply.  This  oxygen  was  accompanied  in  the  excess 
air-supply  with  3.782  times  its  volume  of  nitrogen,  or  3.782  X  3.547 
=  13.415N.  The  difference  between  80.847  and  13.415  =  67.432  is 


36  STEAM-BOILER  ECONOMY. 

the  N"  of  the  air  theoretically  required  to  burn  the  coal  to  CO  and  CO, 
as  in  the  example,  and  the  quotient,  80.847  -r-  67.432  =  1.199,  is  the 
ratio  of  the  total  air-supply  to  that  theoretically  required.  Subtract- 
ing 1  from  this  ratio  and  multiplying  by  100  gives  19.9%  as  the 
calculated  percentage  of  excess  air-supply,  a  close  approximation  to 
the  20%  originally  assumed  in  computing  the  table.  The  formula  for 
computing  the  ratio  of  air-supply  to  that  theoretically  required  for 

N 
the  incomplete  combustion  stated  is  ~ —    ~Qor\  *n  wnicn  N"  an(i  ^2 

are  respectively  the  percentages  of  N  and  0  by  volume  in  the  dry  gas. 
If  all  the  C  had  been  burned  to  C02  the  air  required  for  complete 
combustion  would  have  been  864  -f-  34.56  =  898.56,  and  the  ratio  of 
the  total  air  used,  1036.80  to  898.56  is  1.153,  that  is  15.3%  excess. 
The  formula  for  the  ratio  of  the  total  air  supply  to  that  required  for 
complete  combustion  is 

N 


N-3.  782(0  -JCO)' 

Applying  it  to  the  example, 

80.847 
80.847-3.782(3.547-0.710)  = 


Air  Supply  Required  for  Different  Grades  of  Coal.  —  Taking  50  per 
cent  excess  air  supply  above  the  theoretical  amount  required  to  effect 
complete  combustion,  the  following  formula  may  be  used  to  obtain  the 
amount  of  air  required  for  any  coal  whose  ultimate  analysis  is  known  : 

Lbs.  air  per  Ib.  coal  =  1.5  X  [11.520  +  34.56(H  -  JO)], 

C,  H  and  0  being  respectively  the  carbon,  hydrogen  and  oxygen 
in  1  pound  of  coal,  or  the  percentage  divided  by  100.  Dividing  the 
result  by  combustible  or  by  the  carbon  in  1  pound  of  coal  gives  the 
pounds  of  air  required  per  pound  combustible  or  per  pound  carbon. 

Calculations  of  the  air  supply  for  the  several  varieties  of  coal 
whose  analyses  are  given  in  the  following  table,  give  the  results  shown 
below. 


FUEL  AND  COMBUSTION. 

ULTIMATE  ANALYSIS    OF  COAL   DRIED  AT   105°C. 


37 


Kind  of  Coal  

A  nth. 

Semi- 

Semi- 

Bit.,  Pa. 

Bit., 

Lignite, 

Crude 
Oil 

anth. 

bit. 

Ohio. 

Texas. 

Texas. 

Carbon 

76  86 

78  32 

86  47 

77   10 

75  82 

64  84 

84  8 

Hydrogen            .  .  . 

2  63 

3  63 

4  54 

4  57 

5  06 

4  47 

11  6 

Oxygen          

2  27 

2  25 

2  68 

6  67 

10  47 

16  52 

1  1 

Nitrogen      

0.82 

1.41 

1.08 

1  58 

1  50 

1  30 

0  8 

Sulphur   

0.78 

2.03 

0.57 

0.90 

0  82 

1  44 

1  7 

Ash.. 

16.64 

12.36 

4.66 

9.18 

6.33 

11.43 

POUNDS   AIR   REQUIRED    FOR    COMBUSTION 


Per  Ib.  dry  coal.  .  .  . 
Per  Ib.  combustible. 
Per  Ib   carbon.    .    . 

14.50 
17.39 
18  86 

15.27 
17.42 
19.50 

17.12 
17.96 
19  40 

15.26 
16.81 
19  65 

15.04 
16.05 
19  84 

12.45 
14.06 
19  21 

20.60 
24  29 

Having  the  proximate  analysis  only,  a  close  approximation  to 
the  number  of  pounds  of  air  required  per  pound  of  combustible,  in 
order  to  have  the  air  supply  50  per  cent  in  excess,  is  as  follows : 

Lbs. 

Anthracite  and  semi-anthracite 17.4 

Semi-bituminous 18 .0 

Bituminous,  Pennsylvania 17.0 

Bituminous,  Ohio 16 . 0 

Lignite,  Texas 14 . 0 

Crude  oil,  Texas 20.6 

Heat  Carried  Away  by  the  Dry  Chimney  Gases  per  Pound  of 
Combustible.* 


Temperature  of  Chimney  Gases,  Deg.  Fahr. 

Per  cent 
CO2  in 

Pounds 
Air  per 
Lb.  Com- 

300° 

350° 

400° 

450° 

500° 

550° 

600° 

650° 

Heat  Wasted,  Per  cent  of  Total  Heat  in  Coal. 

'  21.0 

12 

5.2 

6.2 

7.3 

8.7 

9.5 

10.5 

11.6 

12.7 

16.8 

15 

6.0 

7.6 

9.1 

10.3 

11.6 

13.0 

14.3 

15.6 

14.0 

18 

7.2 

9.1 

10.7 

12.2 

13.9 

15.4 

17.0 

17.9 

12.0 

21 

8.7 

10.5 

12.3 

14.2 

16.0 

17.8 

19.5 

21.0 

10.0 

24 

9.9 

12.0 

14.0 

16.1 

18.2 

20.3 

22.4 

24.4 

9.3 

27 

11.1 

13.5 

15.7 

18.1 

20.4 

22.7 

25.0 

27.4 

8.4 

30 

12.4 

14.9 

17.4 

20.0 

22.6 

25.0 

27.8 

30.4 

7.6 

33 

13.5 

16.3 

19.2 

22.0 

24.7 

27.6 

30.5 

33.2 

7.0 

36 

14.7 

17.8 

20.8 

23.9 

27.0 

30.0 

33.0 

36.6 

6.5 

39 

15.9 

19.2 

22.5 

25.8 

29.2 

32.4 

35.7 

39.0 

6.0 

42 

17.1 

20.6 

24.7 

27.7 

31.3 

34.8 

39.4 

42.0 

From  Bulletin  100  of  the  Uehling  Instrument  Co. 


38  STEAM-BOILER  ECONOMY. 

Errors  in  Analysis  of  Furnace  Gas  Shown  by  Computation.*  —  In 
connection  with  an  evaporative  test  of  a  steam  boiler,  the  following 
average  analysis  of  the  chimney  gases  was  reported  by  a  chemist: 

CO2,  8.2;  CO,  0.6;  O,  7.5;  N,  by  difference,  83.7. 

The  ultimate  analysis  of  the  coal  showed  3.6  per  cent  H  in  the  coal, 
dry  and  free  from  ash.  The  air  used  per  pound  of  carbon,  as  found 
by  the  formula: 

3.032N 
Lbs.airperlb.C    =  ^  +  CQ, 

in  which  N,  C02  and  CO  are  percentages  by  volume,  was  28.65  Ibs. 
This  figure  is,  however,  incorrect,  not  on  account  of  any  error  in  the 
formula,  but  on  account  of  an  error  in  the  analysis.  It  may  be  shown 
that  83.7  per  cent  N  in  the  chimney  gas  cannot  be  obtained  by  any 
practicable  method  of  burning  this  coal  with  air. 

The  percentages  of  N  in  the  dry  gas,  by  volume,  due  to  burning 
C  and  H  in  different  proportions,  without  excess  of  air,  are  as  follows  : 


C  burned  to  CO2  ............................  .....  79.  14 

C  burned  to  CO  .................................  65.48 

H  burned  to  H2O  ............  ............  ........  100.00 

CH4  burned  to  CO2  and  H20  .......................  87.  19 

93C+7H  to  C02  and  H2O  .........................  82.0 

96C+4H  to  CO2  and  H20  .........................  81  .0 

84C+16CH4  to  CO2  and  H2O  ....................  .  .  81  .0 

84C+16CH4,  the  CH4  escaping  unburned  ...........  77  .  8 

84C  +  12C+4H,  the  12C  escaping  as  soot  ...........  81  .  3 

We  thus  see  that  there  is  no  way  in  which  this  coal  can  be  burned 
which  will  give  N  higher  than  81.3  per  cent,  and  even  in  the  supposed 
case  in  which  all  the  CH4  is  unburned  and  escapes  in  the  gases  the 
sum  of  N"  and  CH4  is  only  77.8  per  cent. 

All  the  above  calculations  are  based  on  the  assumption  that  there 
is  no  excess  of  air,  but  the  analysis  shows  7.5  per  cent  free  0.  There 
must  therefore  have  been  a  considerable  -excess,  which  would  cause  the 
percentage  of  N  to  be  lower,  and  to  approach  79.14. 

The  only  conclusion  that  can  be  drawn  from  these  calculations 
is  that  the  N"  by  difference  is  largely  in  error,  and  that  the  C02, 
CO,  and  0  reported  are  either  or  all  of  them  too  small.  The  analysis 
being  wrong,  it  is  impossible  to  figure  from  it  the  number  of  pounds 
of  air  per  pound  of  fuel,  or  to  compute  a  heat  balance  from  the 
results  of  the  boiler  test. 

*  Stevens  Institute  Indicator,  Oct.,  1903. 


FUEL  AND  COMBUSTION.  39 

The  CO  reported  is  not  likely  to  be  greatly  in  error,  since  there 
was  such  a  large  excess  of  air.  The  0  also  was  probably  nearly  cor- 
rect, since  the  phosphorus  (which  was  used  in  the  tests)  is  an  excel- 
lent absorbent.  The  greater  part  of  the  error  is  most  likely  to  be 
in  the  C02,  due  to  its  partial  absorption  by  water  in  the  collecting 
tank.  If  we  take  80  per  cent  as  a  probable  figure  for  the  N,  and  add 
the  difference,  3.7,  to  the  C02  we  obtain 

80  X  3.032 
11  Q  4-  Q  6  ==  ail>  P6r  ' 

instead  of  28.65  Ibs.  originally  calculated. 

Analyses  of  furnace  gases  are  frequently  reported  in  which  the 
N"  by  difference  is  given  from  81  to  84,  leading  to  wrong  conclu- 
sions as  to  the  air  used  for  pound  of  fuel.  There  is  a  possibility, 
however,  that  high  percentages  of  nitrogen  (by  difference)  may  be 
obtained  if  samples  of  gas  are  withdrawn  from  the  furnace  during 
the  period  immediately  after  firing,  when  hydrocarbons  are  being 
distilled  rapidly  and  little  or  no  carbon  is  being  burned.  In  that 
case  the  gases  could  be  high  in  hydrocarbons,  and  so  would  increase 
the  apparent  nitrogen  as  reported  in  the  anaylsis. 

The  burning  of  oils  and  of  gases  high  in  hydrogen  makes  a  flue 
gas  high  in  nitrogen  if  burned  without  great  excess  of  air.  A 
petroleum  of  the  composition  85C,  12H,  30,  N  and  S,  burned  with- 
out excess  air  makes  a  gas  containing  84.9N;  and  a  gas,  CH4,  as 
shown  in  the  above  table,  gives  87.19N. 


APPENDIX  TO  CHAPTER  II. 
I.    HEATING  VALUE  OF   SULPHUR    (AS   IRON  PYRITES)    IN  COAL.* 

A  sample  of  Pocahontas  coal  having  a  calorific  value  of  8062 
(calories)  ^and  containing  0.57  per  cent  of  sulphur  was  mixed  with 
pyrites  in  two  proportions,  nine  of  coal  to  one  of  pyrites,  and  eight  of 
coal  to  two  of  pyrites.  The  coal  and  pyrites  were  separately  reduced 
to  fine  powder  and  then  mixed  by  rubbing  in  a  mortar.  The  mix- 
tures were  then  compressed  into  cylinders  for  combustion  in  the  bomb 
[the  Mahler  calorimeter].  The  pyrites  used  was  a  selected  crystal 
of  FeS2. 

The  results  of  the  two  experiments  were  respectively  6140  and 
5150  units  for  the  heat  due  to  a  unit  of  sulphur  as  pyrites. 

These  two  results  do  not  "check"  very  well,  but  it  seems  safe  to 
conclude  that  the  heat  due  to  the  combustion  of  pyrites  in  the  bomb 

*  By  Prof.  N.  W.  Lord.  Trans.  Am.  Inst.  Mining  Engineers,  vol.  xxvii 
1897,  p.  960. 


40  STEAM-BOILER  ECONOMY. 

is  somewhere  about  5500  units  per  unit  of  sulphur.  Of  course  the 
sulphur  is  here  burned  to  S03,  or  rather  to  dilute  H2S04,  and  gives 
more  heat  than  when  it  burns  in  air  to  S02.  Pyrites  contains  53.3 
per  cent  S.  Translating  the  above  result  (5500)  into  heat  developed 
per  unit  of  FeS2  gives  2931  heat  units. 

Berthelot  gives  for  the  heat  of  formation  of  dilute  H2S04  what  is 
equivalent  to  4388  units  per  unit  of  sulphur;  and  assuming  1582  as 
the  heating  value  of  iron  burned  to  magnetic  oxide  (Andrews),  a 
calculation  for  the  heating  value  of  pyrites  would  give: 

0.533S..                                                                                 .   2339 
0.467  Fe 739 

Calculated  heat 3078 

The  S  being  burned  to  dilute  H2S04. 

This  corresponds  to  the  value  found  well  enough  to  show  that 
when  pyrites  burns,  the  iron  and  sulphur  give  nearly  the  same  heat 
they  do  when  burned  separately  in  the  free  state,  which  justifies  the 
introduction  into  Dulong's  formula  of  the  sulphur  term.  As  to  the 
number  I  have  adopted  in  the  formula  (2250)  *  for  the  heat  developed 
when  S  burns  to  S02,  it  was  taken  as  an  average  of  several  published 
figures,  and  is  probably  a  little  too  high,  but  not  enough  out  of  the 
way  to  affect  the  results  noticeably,  especially  as  the  heat  due  to  the 
combustion  of  the  iron  was  omitted,  which  it  would  appear  should 
have  been  included,  though  it  would  have  amounted  to  very  little. 


II.  HYGROMETRIC  PROPERTIES  OF  COALS. | 

Two  lines  of  investigation  were  undertaken  for  the  purpose  of 
ascertaining  the  relative  qualities  of  various  coals  when  in  the  same 
physical  condition  with  reference  to  absorbing  moisture  from  the 
atmosphere. 

First,  a  number  of  samples  of  different  coals  were  reduced  to  a 
uniform  physical  condition  by  grinding  or  powdering;  were  then 
thoroughly  dried,  and  afterward  simultaneously  exposed  to  a  saturated 
or  nearly  saturated  atmosphere,  for  a  period  of  from  six  to  .eight 
days  as  required,  to  obtain  constant  weight.  The  weight  of  moisture 
was  checked  by  thoroughly  drying  and  reweighing. 

Second,  an  investigation  was  made  to  determine  the  effect  of  the 
size  of  particles  upon  the  power  to  absorb  moisture;  the  investigation 
being  similar  in  nature  to  that  previously  described. 

*  The  heat-units  in  this  paper  are  calories  per  gram.  2250  calories  per 
gram  =  4050  B.T.U.  per  Ib. 

t  From  a  paper  by  Prof.  R.  C.  Carpenter  in  Trans.  A.  S.  M.  E.,  vol.  xviii. 
p.  938. 


FUEL  AND  COMBUSTION.  41 

In  drying,  the  coal  was  heated  to  a  temperature  of  from  220  to 
240  degrees  Fahr.,  and  maintained  in  that  condition  for  one  hour. 

Eesults  indicate  a  great  difference  in  the  absorptive  power  of  dif- 
ferent coals  when  in  the  same  physical  state,  but  show,  however,  a 
striking  similarity  in  this  respect  of  coals  which  are  known  to  pos- 
sess similar  qualities  from  the  same  geographical  districts.  With 
few  exceptions,  the  power  of  absorbing  and  retaining  moisture  is  less 
as  the  calorific  value  is  greater. 

The  maximum  amounts  of  moisture  absorbed  by  coals  powdered 
so  as  to  pass  No.  80  sieve  were  as  follows : 

Anthracite. — 10  samples,  4.66  to  6.37%;  average,  5.60%. 

Eastern  Coking  Coals. — 6  samples,  0.69  to  3.16%;  average,  1.92%. 

Illinois  and  Indiana  Coals. — 6  samples,  4.65  to  14.10%;  average,  9.77%. 

In  the  second  investigation  the  pieces  of  coal  were  made  as  nearly 
equal  as  possible  considering  their  irregular  shape  of  definite  sizes. 
The  results  given  below  show  an  increase  in  absorptive  power  as  the 
size  of  the  particle  is  diminished. 

Size      1  in.  Yz  in.  ^  in.  Fine. 

Illinois 4.55  5.80  5.26  9.30 

Cumberland 2.17  3.76  5.61  6.42 

Lehigh  anthracite  egg 1 . 39  2 . 03  2 . 55  5 . 95 

pea 62  .66  1.31  1.59 

In  connection  with  the  drying  of  coals  at  temperatures  above  the 
boiling  point  a  number  of  experiments  were  made  to  determine 
whether  there  was  any  sensible  loss  of  volatile  matter,  but  so  far  as 
could  be  determined  by  repeated  trials  alternately  drying  and  moisten- 
ing and  by  varying  time  of  drying  from  one  to  three  hours,  no  loss  of 
volatile  matter  could  be  detected,  and  it  seems  exceedingly  probable 
that  no  loss  of  importance  occurs  at  temperatures  below  300°  F. 

For  this  reason  it  would  seem  entirely  safe  to  use  this  method  of 
drying  coals  in  testing-boilers,  as  it  is  easily  applied,  and  has  given 
very  satisfactory  and  uniform  results  for  the  writer  whenever  used, 


CHAPTER  III. 


COAL. 

Production  of  Coal  in  the  United  States.— The  extent  of  the  coal 
industry  of  the  United  States,  which  keeps  pace  with  the  growth  of 
manufacturing  and  with  the  increase  of  wealth,  is  shown  by  the  follow- 
ing figures  taken  from  "Mineral  Resources  of  the  United  States  for 
the  Calendar  Year  1910"  published  by  the  U.  S.  Geological  Survey. 

[COAL  PRODUCTION  OF  THE  UNITED  STATES  IN  1910,  BY  STATES,  IN  SHORT  TONS.* 


State  or  Territory. 

Total 
Quantity. 

Total 
Value. 

Average 
Price  per 
Ton  at  the 
Mine. 

Average 
Number  of 
Employees. 

Alabama, 

16,111,462 

$20,236  853 

$1  26 

22  230 

Arkansas  
California  and  Alaska. 

1,905,958 
12,164 

2,979,213 
33336 

1.56 
2  74 

5,568 

10 

Colorado 

11,973,736 

17,026,934 

42 

15  864 

Georgia 

177,245 

259,122 

46 

386 

Idaho 

4,448 

17426 

92 

14 

Illinois 

45  900,246 

52,405  897 

14 

72  645 

Indiana 

18,389,815 

20,813  659 

13 

21  878 

Iowa  

7,928,120 

13,903,913 

.75 

16666 

Kansas  

4,921,451 

7,914,709 

61 

12870 

Kentucky  

14,623,319 

14,405,887 

.99 

20316 

Maryland  

5,217,125 

5,835,058 

.12 

5809 

Michigan  

1,534,967 

2,930,771 

.91 

3575 

Missouri  
Montana  

2,982,433 
2,920,970 

5,328,285 
5,329,322 

.79 

.82 

9,691 
3,837 

New  Mexico  
North  Dakota  

3,508,321 
399,041 

4,877,151 
595,139 

1.39 
1.49 

3,585 
534 

Ohio  

34,209,668 

35,932,288 

1.05 

46641 

Oklahoma  
Oregon  
Pennsylvania,  bituminous  .... 
Tennessee  
Texas  

2,646,226 
67,533 
150,521,526 
7,121,380 
1,892,176 

5,867,947 
235,229 
153,029,510 
7,925,350 
3,160,965 

2.22 
3.48 
1.02 
1.11 
1.67 

8,657 
153 
175,403 
11,930 
4  197 

Utah  

2,517,809 

4,224,556 

1  68 

3,053 

Virginia  

6,507,997 

5,877,486 

90 

7.264 

Washington  

3,911,899 

9,764,465 

2  50 

6,314 

West  Virginia  

61,671,019 

56,665,061 

92 

68,663 

Wyoming  

7,533,088 

11,706,187 

1  55 

7,771 

Total  bituminous  f  .  .  .  . 
Pennsylvania,  anthracite  

417,111,142 

84,485,236 

469,281,719 
160,275,302 

1.12 
1.90 

555,533 
169,497 

Grand  total    .  . 

501,596,378 

629,557,021 

1  25 

725,030 

*  Short  tons,  2000  Ibs.,  are  used  in  the  government  statistics;  long  or  gross  tons,  2240  Ibs., 
are  commonly  used  in  the  trade. 

t  Includes    semi-bituminoua,    sub-bituminous,    and    lignite,    and    all    anthracites    except 
Pennsylvania, 

42 


COAL. 


43 


COAL  PRODUCTION  OF  THE   UNITED  STATES  IN   1910. — Continued. 


Bituminous. 

Anthracite. 

Total. 

Tons  loaded  at  mines  for  shipment 

342  969  220 

73  623  227 

41  A  e,QO  447 

Sold  to  local  trade  and  used  by  employees 
Used  at  mines  for  steam  and  heat  
Made  into  coke  

12,286,851 
9,667,621 
52,187,450 

2,020,572 

8,841,437 

14,307,423 
18,509,058 
52,187,450 

Total     

417,111,142 

84,485  236 

501  596  378 

To  the  value  of  coal  at  the  mine,  averaging  $1.25  per  ton  according 
to  the  table  on  page  42,  must  be  added  the  freight  charge  to  obtain 
its  cost  to  the  consumer.  If  this  charge  averages  $1.00  per  ton,  prob- 
ably too  low  a  figure,  it  makes  the  total  cost  of  coal  consumed  in  the 
United  States  over  1100  millions  of  dollars  per  annum. 

The  average  number  of  days  in  the  year  in  which  the  mines  were 
active  was  220;  in  the  bituminous  region  217,  in  the  anthracite  229. 

In  several  States  in  the  Middle  West  the  production  of  1910  was 
much  less  than  that  of  1909  on  account  of  a  miners'  strike  of  long 
duration.  The  States  that  showed  a  large  decrease  in  1910  gave  the 
following  tonnage  in  1909  : 


Arkansas 2,377,157  tons 

Illinois 50,904,990    ' ' 

Kansas 6,986,478    " 


Michigan 1,784,692  tons 

Missouri 3,756,530    " 

Oklahoma 3,119,377    " 


PRODUCTION  OF  COAL  IN  THE  UNITED  STATES  PROM  1820  TO  1910,  IN  SHORT  TONS. 


Pennsyl- 

Pennsyl- 

Year. 

vania 

Bituminous. 

Total. 

Year. 

vania 

Bituminous. 

Total. 

Anthracite. 

Anthracite. 

1820 

450 

3,000 

3,450 

1901 

67,471,667 

225,828,149 

293,299,816 

1830 

215,272 

104,800 

320,072 

1902 

41,373,595 

260,216,844 

301,590,439 

1840 

967,108 

1,102,931 

2,070,039 

1903 

74,607,068 

282,749,348 

357,356,416 

1850 

4,138,164 

2,880,017 

7,018,181 

1904 

73,156,709 

278,659,689 

351,816,398 

1860 

8,115,842 

6,494,200 

14,610,042 

1905 

77,659,850 

315,062,785 

392,722,635 

1870 

15,664,275 

17,371,305 

33,035,580 

1906 

71,282,411 

342,874,867 

414,157,278 

1880 

28,649,812 

42,831,758 

71,481,570 

1907 

85,604,312 

394,759,112 

480,363,424 

1885 

38,335,974 

72,824,321 

111,160,295 

1908 

83,268,754 

332,573,944 

415,842,698 

1890 

46,468,641 

111,302,322 

157,770,963 

1909 

81,070,359 

379,744,257 

460,814,616 

1895 

57,999,337 

135,118,193 

193,117,530 

1910 

84,485,236 

417,111,142 

501,596,378 

1900 

57,367,915 

212,316,112 

269,684,027 

PRODUCTION  OF  COAL  PER  CAPITA  IN  THE   UNITED  STATES    (MINERAL  RESOURCES, 

1910). 

Year 1850         1860       1870       1880       1890       1900       1910 

Short  tons  per  capita..  ..  0.278      0.514      0.96       1.52      2.52      3.53      5.45 

The  rate  of  increase  in  the  production  of  anthracite  is  now  not 
materially  different  from  "the  rate  of  increase  in  population.     An- 


44  STEAM-BOILER  ECONOMY. 

thracite  is  rapidly  being  supplanted  by  bituminous  coal  as  a  fuel  for 
manufacturing  purposes  as  its  cost  of  production  increases. 


AVERAGE  YEARLY  PRODUCTION  OP  COAL  IN  THE    UNITED  STATES  FOR  EACH  DECADE 


Years. 

Short  Tons. 

Years. 

Short  Tons. 

1814-1845 
1846-1855 
1856-1865 
1866-1875 

864,913 
8,341,783 
17,379,502 
41,942,511 

1876-1885 
1886-1895 
1896-1905 
1906-1910 

(5  years) 

84,776,032 
158,609,864 
283,240,275 
454,554,879 

WORLD'S  PRODUCTION  OP  COAL  (TOTAL  ABOUT  1,300,000,000  SHORT  TONS). 


Country. 

Year. 

Short  Tons. 

Country. 

Year. 

Short  Tons. 

United  States.  .  .  . 

1910 

501,596,378 

Spain 

1909 

4,546,713 

Great  Britain  .... 
Germany  

1910 
1910 

296,007,699 
245,043,120 

Transvaal  
Natal 

1910 
1910 

4,446,477 
2,572,012 

Austro-Hungary  . 
France  

1909 
1910 

54,573,788 
42,516,232 

New  Zealand.  .... 
Mexico 

1909 
1909 

2,140,597 
1,432,990 

Belgium    

1910 

26,374,986 

Holland 

1909 

1,235,515 

Russia  and 
Finland    .  . 

1910 

24,967  095 

Queensland  and 
Victoria 

1909 

1,119  708 

Japan      

1909 

16,505,418 

Italy 

1909 

611  857 

India              ..... 

1909 

13,294,528 

Sweden 

1909 

272  056 

China          .      ... 

1909 

13,227,600 

Cape  Colony 

1909 

103  519 

Canada  
New  South  Wales. 

1910 
1909 

12,796,512 
7,862,264 

Tasmania  
Other  countries.  .  . 

1909 

93,845 
5,236,903 

Formation  of  Coal. — According  to  the  geologists  a  piece  of  coal 
was  many  thousands  of  years  ago  a  mass  of  damp  vegetable  fibre,  a 
portion  of  a  peat-bog.  Half  of  its  weight,  approximately,  was  water, 
and  the  other  half  would  contain,  by  analysis,  about  50%  carbon,  6% 
hydrogen,  40%  oxygen,  1%  nitrogen,  and  2%  ash.  During  successive 
geologic  ages  the  peat-bog  was  submerged  and  overlaid  with  mud, 
which  hardened  into  slate.  This  was  covered  with  glacial  and  alluvial 
drift,  and  it  may  have  been  tilted  and  upheaved  by  volcanic  action  or 
subsidence  of  the  earth's  crust.  It  was  subjected  to  great  pressure 
and  high  temperature,  and  underwent  a  more  or  less  complete  destruc- 
tive distillation  under  pressure. 

The  conditions  under  which  the  distillation  of  the  peat-bogs  took 
place  were  not  alike  in  different  parts  of  the  world.  The  variable 
factors  were  time,  depth  and  porosity  of  the  overlying  strata,  pressure 
and  temperature,  disturbance  of  the  beds  by  floods  and  by  intrusion 


COAL. 


45 


into  them  of  minerals,  such  as  carbonate  of  lime  held  in  solution,  or 
clay,  sand,  iron,  and  sulphur.  Therefore  the  product  of  the  distillation 
varies  in  different  locations  all  the  way  from  the  original  peat  through 
brown  coal  or  lignite,  bituminous  and  semi-bituminous  coal,  semi- 
anthracite  and  anthracite,  to  graphitic  coal.  The  last-named,  which 
is  found  in  Rhode  Island,  has  nearly  all  the  volatile  hydrocarbon  gases 
and  oxygen  driven  off  from  it,  leaving  practically  only  fixed  carbon 
and  ash,  the  carbon  being  in  a  form  which  is  so  hard  to  burn  that  the 
coal  is  not  used  as  a  commercial  fuel;  while  the  first,  lignite,  is  only 
one  remove  from  the  peat  or  woody  fibre,  retaining  perhaps  a  third  of 
the  water,  and  a  large  part  of  the  original  hydrocarbon,  or  rather  oxy- 
hydrocarbon,  since  it  contains  a  large  percentage  of  oxygen,  The 
progresive  change  in  chemical  analysis,  from  wood  to  coal,  is  shown 
in  the  two  following  tables: 

DIMINUTION   OF   H    AND    O   IN   SERIES   FROM   WOOD   TO    ANTHRACITE.* 


Substance. 

Carbon. 

Hydrogen. 

Oxygen. 

Woody  fibre          

52  65 

5  25 

42   10 

Peat  from  Vulcaire  

59.57 

5  96 

34.47 

Lignite  from  Cologne  

66.04 

5  27 

28  69 

Earthy  brown  coal  .  .  .  .  ,  
Coal  from  Belestat,  secondary  

73.18 
75.06 

5.58 
5.84 

21.14 
19.10 

Coal  from  Rive  de  Gier 

89  29 

5  05 

5  66 

Anthracite,  Mayenne,  transition  formation  

91.58 

3.96 

4.46 

*  Groves  and  Thorpe's  Chemical  -Technology,  vol.  i.  Fuels,  p.  58. 


PROGRESSIVE   CHANGE   FROM   WOOD   TO   GRAPHITE,  f 


Wood. 

Loss. 

Lignite. 

Loss. 

Bit.  coal. 

Loss. 

Anthra- 
cite. 

Loss. 

Graphite. 

Carbon 

49.1 
6.3 
44.6 

100.0 

18.65 
3.25 
24.40 

30.45 
3.05 
20.20 

12.35 
1.85 
18.13 

18.10 
1.20 
2.07 

3.57 
0.93 
1.32 

14.53 
0.27 
0.65 

1.42 
0.14 
0.65 

13.11 
0.13 
0.00 

Hydrogen 

Oxygen  

46.30 

53.70 

32.33 

21.37 

5.82 

15.45 

2.21 

13.24 

t  J.  S.  Newberry  in  Johnson's  Cyclopedia. 

We  thus  have  different  varieties  of  coal,  due  to  differences  in  the 
extent  to  which  the  volatile  gases  have  been  driven  off  from  the 
original  neat  or  other  woody  coal-forming  substance.  There  are  also 
differences  in  quality  in  each  variety,  due  to  varying  percentages  of 
ash  and  water.  The  ash,  or  earthy  matter,  in  coal  ranges  from  2  to 


46 


STEAM-BOILER  ECONOMY. 


over  30%  in  different  localities.  The  water  ranges  from  less  than 
1%  in  the  anthracites  up  to  14%  or  more  in  some  Illinois  coals  and  to 
25%  or  more  in  some  lignites.  This  water  seems  to  be  held  by  capil- 
lary attraction,  or  some  similar  force,  within  the  particles  of  a  piece  of 
apparently  dry  coal,  so  that  it  cannot  all  be  driven  off  without  heating 
it  to  a  temperature  considerably  higher  than  212°  F.,  say  250°  to 
280°  F.  The  bituminous  coals  are  hygroscopic,  like  wood  ;*  that  is, 
they  absorb  moisture  from  the  atmosphere,  and  the  quantity  they  will 
contain  depends  not  only  on  the  nature  of  the  coal,  but  on  the  relative 
humidity  of  the  atmosphere,  which  changes  from  day  to  day. 

Classification  of  Coal. — It  is  convenient  to  classify  the  several 
varieties  of  coal  according  to  the  relative  percentages  of  carbon  and 
volatile  mater  contained  in  their  combustible  portion  as  determined 
by  proximate  analysis.  The  following  is  such  a  classification:! 


Fixed 
Carbon. 

Volatile 
Matter. 

Heating  Value  per 
Lb.  Combustible. 

Relative  Value  ' 
of  Combustible 
Semi-bit.  =  100. 

Anthracite  

97  to  90 

3  to  10 

14,800  to  15,400 

93 

Semi-anthracite  
Semi-bituminous  .... 
Bituminous,  Eastern  . 
Western. 
Lignite           

90  to  85 
85  to  70 
70  to  55 
65  to  50 
under  50 

10  to  15 
15  to  30 
30  to  45 
35  to  50 
over  50 

15,400  to  15,500 
15,400  to  16,000 
14,800  to  15,600 
12,500  to  14,800 
11,000  to  13,500 

97 
100 
96 
90 

77 

The  locations  in  which  the  several  classes  of  coal  are  found  are 
destribed  in  some  detail  in  the  chapter  on  Coal-fields  of  the  United 
States.  The  anthracites,  with  some  unimportant  exceptions,  are  con- 

*  Note  on  the  Hygroscopicity  of  Wood  (from  Johnson's  Materials  of  Con- 
struction, p.  224). — Kept  on  a  shelf  in  an  ordinary  dwelling,  wood  still  retains 
8  to  10%  of  its  weight  of  water.  Nor  is  the  amount  of  water  in  dry  wood 
constant;  the  weight  of  a  panful  of  shavings  varies  with  the  time  of  day,  being 
on  a  summer  day  greatest  in  the  morning  and  least  in  the  afternoon. 

Desiccating  the  air  with  chemicals  will  cause  the  wood  to  dry,  but  wood 
thus  dried  at  80°  F.  will  still  lose  water  in  the  kiln.  Wood  dried  at  120°  F. 
loses  water  still  if  dried  at  200°  F.,  and  this  again  will  lose  more  water  if  the 
temperature  is  raised.  Absolutely  dry  wood  cannot  be  obtained;  chemical 
destruction  sets  in  before  all  water  is  driven  off. 

On  removal  from  the  kiln  the  wood  at  once  takes  up  water  from  the  air, 
even  in  the  driest  weather.  At  first  the  absorption  is  quite  rapid;  at  the  end 
of  a  week  a  short  piece  of  pine,  1£  in-  thick,  has  regained  two-thirds  of,  and 
in  a  few  months  all,  the  moisture  it  has  when  air-dry,  8  to  10%,  and  also  its 
former  dimensions. 

f  A  more  satisfactory  classification  will  be  found  on  page  58. 


COAL.  47 

fined  to  three  small  fields  in  eastern  Pennsylvania.  The  semi-anthra- 
cites are  found  in  a  few  small  areas  in  the  western  part  of  the  anthra- 
cite field.  The  semi-bituminous  coals  are  found  in  a  narrow  strip  of 
territory,  20  miles  wide  or  Less,  on  the  eastern  border  of  the  great 
Appalachian  coalfield,  extending  from  north-central  Pennsylvania 
across  the  southern  boundary  of  Virginia  into  Tennessee,  a  distance 
of  over  300  miles. 

It  is  a  peculiarity  of  these  semi-bituminous  coals  that  their  com- 
bustible portion  is  of  remarkably  uniform  composition,  the  volatile 
matter  usually  ranging  between  18  and  22  per  cent  of  the  combustible, 
and  approaching  in  its  anaylsis  marsh-gas,  CH4,  with  very  little 
oxygen.  They  are  usually  low  also  in  moisture,  ash,  and  sulphur,  and 
rank  among  the  best  steam-coals  in  the  world.  The  eastern  bituminous 
coals  occupy  the  remainder  of  the  Appalachian  coal-field,  from  Penn- 
sylvania and  eastern  Ohio  to  Alabama.  They  are  higher  in  volatile 
matter,  ranging  from  30  to  over  40  per  cent,  the  higher  figures  in  the 
western  portion  of  the  field.  The  volatile  matter  is  of  lower  heating 
value,  being  higher  in  oxygen.  The  Western  bituminous  coals  and 
lignites  are  found  in  most  of  the  States  west  of  Ohio.  They  are 
higher  in  volatile  matter  and  in  oxygen  and  moisture  than  the  bitu- 
minous coals  of  the  Appalachian  field,  and  usually  give  off  a  denser 
smoke  when  burned  in  ordinary  furnaces. 

The  U.  S.  Geological  Survey  recognizes  six  classes  of  coal.  They 
are  described  as  follows  by  Prof.  N.  W.  Lord  (Power),  Aug.  18, 
1908)  : 

(1)  Anthracite,  (2)  semi-anthracite,  (3)  semi-bituminous,  (4) 
bituminous,  (5)  sub-bituminous  or  black  lignite,  and  (6)  lignite. 
While  this  classification  is  generally  useful,  it  is  difficult  to  draw  fast 
and  sharp  lines  in  the  classification,  as  samples  are  found  on  the  bor- 
der lines  of  almost  any  system  of  classification.  The  general  qualities 
of  these  types  of  fuel  correspond  well  to  the  coals  of  certain  regions, 
as  the  anthracites  of  Pennsylvania,  the  coking  bituminous  coals  of 
Pennsylvania,  the  non-coking  bituminous  coals  of  Ohio  and  Illinois. 
Coals  differ  widely  not  only  in  their  physical  characteristics,  their  be- 
havior under  a  destructive  distillation,  some  cementing  together  into  a 
hard  coke  or  possessing  the  coking  property,  as  it  is  termed,  others,  the 
so-called  dry  coals,  showing  but  little  or  none  of  this  quality,  but  also 
in  their  chemical  composition  and  in  their  associated  impurities. 

The  proximate  analysis  of  coal  is  merely  a  record  of  the  nature 
of  the  decomposition  that  the  coal  undergoes  when  treated  in  a  certain 


48 


STEAM-BOILER  ECONOMY. 


conventional  manner.  It  involves  the  determination  of  the  moisture 
or  loss  in  weight  when  the  coal  is  dried  under  certain  specific  con- 
ditions; of  the  volatile  combustible  matter  or  the  material  other  than 
moisture  which  is  driven  off  by  heating  the  coal  in  a  prescribed  way 
in  a  platinum  crucible ;  the  fixed  carbon,  which  is  the  loss  in  weight 
of  the  residue  after  driving,  out  the  volatile  matter  when  the  com- 
bustible matter  is  all  burned  out  by  heating  in  air;  and,  finally,  the 
ash  or  combustible  residue  left  from  the  foregoing  treatment. 

In  the  ultimate  analysis  of  the  coal  the  actual  percentages  of 
carbon,  hydrogen,  nitrogen,  sulphur,  oxygen  and  incombustible  residue 
or  ash  are  determined.  The  heating  value  of  a  coal  is  the  amount  of 
heat  expressed  in  British  thermal  units  developed  by  the  complete 
combusion  of  one  pound  of  the  coal,  and  for  all  purposes  in  which 
coal  is  used  as  a  fuel  is,  of  course,  the  fundamental  factor  on  which 
the  fuel  value  of  the  material  is  based.  The  following  table  gives 

COMPOSITION   OF  ILLUSTRATIVE   COALS. 


Ultimate  Proximate 
*  analysis,  t  analysis.* 

Class. 

1 

2 

3 

4 

5 

6 

7 

Moisture  
Volatile  combustible  .  .  . 
Fixed  carbon  

2.08 
7.27 
74.32 
16.33 

1.28 
12.82 
73.69 
12.2-1 

0.65 

18.80 
75.92 
4.63 

0.97 
29.09 
60.85 
9.09 

7.55 
34.03 
52.57 
5.85 

8.68 
41.31 
46.49 
3.52 

9.88 
36.17 
43.65 
10.30 

4sh            

Loss  in  air  drying  
Hydrogen        

3.40 

2.63 

76.86 
2.27 
0.82 
0.78 
16.64 

12,472 

1.10 

3.63 
78.32 
2.25 
1.41 
2.03 
12.36 

13,406 

1.10 

4.54 
86.47 
2.68 
1.08 
0.57 
4.66 

15,190 

4.20 

4.57 
77.10 
6.67 
1.58 
0.90 
9.18 

13,951 

Undet. 

5.06 
75.82 
10.47 
1.50 
0.82 
6.33 

12,510 

11.30 

5.31 
73.31 
15.72 
1.21 
0.60 
3.85 

11,620 

23.50 

4.47 
64.84 
16.52 
1.30 
1.44 
11.43 

10,288 

Carbon          

Oxygen              

Nitrogen           

Sulphur         

Ash                    

Calorific  value  in  B.T.U. 

Air-dried  sample. 


t  Coal-dried  at  105°  C. 


RESULTS  CALCULATED  TO  ASH  AND  MOISTURE-FREE  BASIS. 


1 

Volatile  combustible  .  .  . 

•8.91 

14.82 

19.85 

32.34 

39.30 

47.05 

45.31 

.1 

Fixed  carbon  

91.09 

85.18 

80.15 

67.66 

60.70 

52.95 

54.69 

I 

PH 

Hydrogen              

3.16 

4.14 

4.76 

5.03 

5.41 

5.50 

5.05 

Carbon                  

92.20 

89.36 

90.70 

84.89 

80.93 

76.35 

73.21 

Oxygen              

2.72 

2.57 

2.81 

7.34 

11.18 

16.28 

18.65 

1 

Nitrogen           

0.98 

1.61 

1.13 

1.74 

1.61 

1.25 

1.47 

e 

Sulphur  

0.94 

2.32 

0.60 

1.00 

0.87 

0.62 

1.62 

Calorific  value  in  B.T.U. 

15,281 

15,496 

15,744 

15,512 

14,446 

13,203 

12,889 

COAL.  49 

the  proximate  and  ultimate  analyses  and  the  heating  value  of  a  typical 
coal  in  each  of  the  foregoing  six  classes.  The  coals  given  in  the  table 
are: 

1.  Anthracite,  culm,  Scranton,  Penn.  2.  Semi-anthracite,  Coal- 
hill,  Ark.  3.  Semi-bituminous,  Mora,  W.  Ya.  4.  Bituminous  cok- 
ing, near  Connellsville,  Penn.  5.  Bituminous  non-coking,  Ohio  No. 
6,  Hocking  Valley.  6.  Sub-bituminous,  black  lignite,  Uinta  County, 
Wyoming.  7.  Lignite,  Milan  County,  Texas.* 

It  will  be  seen  that  there  is  a  progressive  change,  consisting  of  a 
decrease  in  the  fixed  carbon  and  increase  in  the  volatile  matter,  and 
in  the  ultimate  analysis,  an  increase  in  the  amount  of  oxygen  and 
hydrogen.  The  maximum  heating  value  rests  with  the  semi-bitu- 
minous coals  of  the  Pocahontas  type,  high  in  fixed  carbon  and  com- 
paratively low  in  volatile  matter.  The  amount  of  moisture  varies  with 
the  type  of  coal,  but  only  in  a  very  general  way.  Coals  freshly  mined 
contain  considerable  water,  which  is  rapidly  lost  on  exposure  to  air. 
The  analyses  are  reported  upon  the  coal  in  approximately  the  con- 
dition of  moisture  to  which  it  will  attain  upon  standing  exposed  to 
the  ordinary  air,  the  coal  being  in  a  coarsely  crushed  condition.  If 
the  coal  be  considered  as  made  up  of  three  main  constituents:  mois- 
ture, the  combustible  portion  or  true  coal,  and  the  ash,  the  typical 
analyses  of  the  various  groups  may  be  corrected  by  eliminating  by 
calculation  the  amount  of  moisture  and  ash  and  restating  the  com- 
position of  the  remainder  considered  as  coal.  This  is  done  in  the 
latter  part  of  the  table. 

With  the  analyses  thus  given  the  progressive  changes  in  the  com- 
position become  much  more  apparent  and  uniform,  particularly  the 
progressive  increase  in  volatile  matter  and  decrease  in  fixed  carbon. 
The  heating  value  of  the  combustible  portion  is  highest  in  the  semi- 
bituminous,  class  3. 

The  sulphur  in  the  coal  may  be  regarded  as  one  of  its  impurities, 
though  in  many  cases  a  considerable  portion  of  it  is  an  inherent  part 
of  the  coal  proper,  only  a  portion  of  it  existing  as  iron  pyrites.  In 

*  The  coal  classed  as  anthracite  in  the  above  table,  No.  1,  is  higher  in 
volatile  matter  than  most  of  the  Pennsylvania  anthracites.  In  some  early 
classifications  it  would  be  called  a  semi-anthracite.  The  two  bituminous  coals 
4a  and  46  differ  more  both  in  composition  and  in  heating  value  than  the  sub- 
bituminous,  No.  5,  coal  and  the  lignite,  No.  6.  It  is  evident  that  in  any  sys- 
tem of  classification,  one  class  will  overlap  another,  and  no  strict  lines  of  division 
can  be  drawn  between  the  several  classes. 


50  STEAM-BOILER  ECONOMY. 

many  coals,  on  the  contrary,  a  large  percentage  of  the  sulphur  present 
is  simply  mechanically  mixed  pyrites.  The  foregoing  outline  serves 
to  show  that  the  coal  from  any  district  or  mine  may  be  considered  as 
made  up  of  coal  proper  and  a  certain  amount  of  mechanically  held 
impurities,  consisting  of  ash,  moisture,  and  sulphur  in  the  form  of 
pyrites. 

The  character  of  the  coal  proper  is  much  less  subject  to  variation 
in  the  mines  of  a  given  seam  in  a  given  district  than  are  the  relative 
proportions  of  the  impurities,  particularly  ash  and  sulphur,  which 
vary  greatly  in  different  portions  of  the  same  seam  and  frequently 
vary  considerably  from  one  portion  of  a  field  to  the  other.  An  inter- 
esting example  of  this  is  found  in  the  Middle  Kittanning  coal,  of 
the  Ohio  series,  in  which  the  sulphur  in  certain  portions  of  the  seam 
covering  areas  of  many  square  miles  in  extent  will  run  under  1  per 
cent,  the  amount  increasing,  however,  as  the  seam  extends  northward 
until  regions  are  reached  where  for  the  same  coal  the  average  sulphur 
content  is  over  5  per  cent.  Variations  in  the  ash  take  place  in  the 
same  way. 

Caking  and  Non-caking  Coals. — Bituminous  coals  are  sometimes 
classified  as  caking  and  non-caking  coals,  according  to  their  behavior 
when  subjected  to  the  process  of  coking.  The  former  undergo  an 
incipient  fusion  or  softening  when  heated,  so  that  the  fragments 
coalesce  and  yield  a  compact  coke,  while  the  latter  (also  called  free- 
burning)  preserve  their  form,  producing  a  coke  which  is  only  service- 
able when  made  from  large  pieces  of  coal,  the  smaller  pieces  being 
incoherent.  The  reason  of  this  difference  is  not  clearly  made  out,  as 
non-caking  coals  are  often  of  very  similar  ultimate  chemical  composi- 
tion to  those  in  which  the  caking  property  is  very  highly  developed. 
It  is  found  that  caking  coals  lose  that  property  when  exposed  to  the 
air  for  a  lengthened  period,  or  by  heating  to  about  570°  F.,  and  that 
the  dust  or  slack  of  non-caking  coal  may,  in  some  instances,  be  con- 
verted into  a  coherent  cake  by  exposing  it  suddenly  to  a  very  high 
temperature.  Some  coals  which  cannot  be  made  into  coke  in  the  bee- 
hive ovens  are  easily  choked  in  modern  gas-heated  ovens.* 

Long-flaming  and  Short-flaming  Coals. — The  distinction  between 
long-flaming  and  short-flaming  coals  is  one  commonly  made  by  Eu- 
ropean writers,  but  it  is  not  often  made  in  this  country.,  A  long- 

*  For  a  discussion  of  the  relation  of  the  chemical  composition  to  the  coking 
property  see  Bulletin  29  of  the  U.  S.  Bureau  of  Mines,  1911,  The  Effect  of 
Oxygen  in  Coal,  by  David  White. 


COAL.  51 

flaming  coal  is  simply  one  having  a  high  percentage  of  volatile  matter, 
and  which  gives  off  a  long  flame  when  burned  in  an  ordinary  furnace 
on  account  of  the  difficulty  of  supplying  the  volatile  matter  with  a 
sufficient  quantity  of  hot  air  to  cause  its  complete  combustion.  The 
same  coal  will  give  a  short  flame  when  burned  in  an  underfeed  stoker 
furnace  with  an  adequate  supply  of  air. 

Bituminous  Coal  contains  no  Bitumen. — The  solvents  for  bitumi- 
nous substances,  such  as  bisulphide  of  carbon  and  benzole,  have  no 
effect  upon  bituminous  coals. 

J.  C.  W.  Frazer  and  E.  J.  Hoffman  (Technical  Paper  No.  5,  of 
the  Bureau  of  Mines,  1912)  obtained  a  tarry  substance  amounting  to 
nearly  11  per  cent  of  the  original  weight,  by  extracting  an  Illinois 
coal  with  phenol.  This  was  separated  by  treatment  with  various  sol- 
vents into  a  great  number  of  other  substances,  some  of  which  appear 
to  approach  pure  compounds.  Pyridin  and  anilin  have  also  been  used 
to  extract  soluble  constituents  from  coal.  The  investigation  is  incom- 
plete. 

Cannel-coals  are  bituminous  coals  that  are  higher  in  hydrogen  than 
ordinary  coals.  They  are  valuable  as  ' l  enrichers  "  in  gas-making. 

ULTIMATE   ANALYSIS  OF  SOME  CANNEL-COALS. 

COMBUSTIBLE. 


C.  H.      O+N.         S.          Ash.  C.  H.        O+N 

Boghead,  Scotland...  63.10      8.91     7.25    0.96     19.78     79.61     11.24    9.15 

Albertite,Nova  Scotia  82 . 67      9.14     8.19     82 . 67      9 . 14    8.19 

Tasmanite, Tasmania  79.34     10.41     4.93    5.32     83.80    10.99    5.21 

LIGNITE   OR  BROWN   COAL    (HIGH   IN  OXYGEN). 

Cologne 63.29      4.9826.24     ....       8.49     66.97      5.2727.76 

Bovey  Devonshire.  .   66.31       5.6323.43     2.36      2.36     69.53      5.9024.57 

Trifail,  Styria 50.72      5.3435.98    0.90      7.86     55.11       5.8039.09 

The  above  analyses  do  not  give  the  water  or  hygroscopic  moisturo. 

Sub-bituminous  Coal  and  Lignite.— The  term  lignite  is  commonly 
given  to  all  the  coals  which  are  intermediate  in  properties  between 
peat  and  the  coals  of  the  older  formations.  They  are  characterized 
by  high  moisture  and  oxygen,  and  are  therefore  lower  in  heating  value 
than  bituminous  coal.  The  names  "black  lignite,"  "brown  lignite," 
"brown  coal/'  and  "lignitic  coal"  have  also  been  given  indiscriminately 
to  all  these  coals.  The  U.  S.  Geological  Survey  divides  them  into  two 
varieties,  sub-bituminous  coal  and  lignite.  They  are  thus  distin- 


52  STEAM-BOILER  ECONOMY. 

guished:  sub-bituminous  coal  is  black  or  grayish  black  in  color;  is 
high  in  moisture,  which  is  given  off  readily  on  exposure  to  sun  or  air, 
producing  "weathering"  or  "slacking";  has  no  distinct  system  of 
joints,  but  has  a  tendency  to  separate  on  weathering  into  thin  plates 
parallel  to  the  bedding.  The  fresh  coal  has  a  bright  luster  and  an 
irregular  conchoidal  fracture;  the  resulting  fragments  are  lusterless 
and  their  surfaces  do  not  show  an  even  fracture  of  any  kind.  Cer- 
tain sub-bituminous  coals  have  high  heating  value  and  will  stand 
transportation  in  closed  cars  without  slacking,  but  will  check  slightly 
when  exposed  to  the  rays  of  the  sun  in  open  cars. 

Lignite  is  brown  in  color  or  has  a  distinctly  brownish  cast.  The 
texture  is  more  or  less  distinctly  woody,  although  some  lignite,  notably 
that  of  Texas,  is  amorphous.  The  amount  of  moisture  is  greater  than 
that  of  sub-bituminous  coal,  and  ranges  from  25  to  nearly  45  per  cent. 

Decrease  of  Weight  of  Lignite  in  Transit.  (A.  C.  Scott,  Power, 
May  11,  1909.) — Contention  between  shippers  and  consumers  of 
lignite  concerning  shortage  in  weights  of  carloads  delivered  is  in 
many  instances  due  to  misunderstandings,  first,  as  to  the  necessary 
decrease  in  weight  that  must  occur  in  transit  due  to  the  properties 
of  the  lignite  and,  second,  as  to  the  fact  that  a  smaller  weight  of 
lignite  at  the  consumer's  plant  as  compared  with  the  weight  at  the 
mine  does  not  necessarily  mean  that  the  consumer  has  lost  money 
in  proportion  to  the  shortage ;  on  the  contrary,  the  consumer  is  actually 
the  gainer  in  the  transaction,  provided  the  loss  in  weight  is  not  ab- 
normal. 

Three  samples  of  lignite  were  taken  from  a  mine  and  tested  for 
moisture  immediately  after  the  jars  were  opened,  with  the  following 
results : 

No.  1,  28.2%;  No.  2,  28.0%;  No.  3,  32.2%,. 

A  lump  of  the  lignite  was  soaked  for  24  hours  in  water,  and  subse- 
quently a  test  showed  39.1%  moisture.  This  indicates  that,  taking 
the  average  moisture  content  of  the  three  samples  at  29.4%,  it  is 
possible  for  the  lignite  to  contain  9.7%  more  moisture  than  it  does 
contain  after  it  is  taken  directly  from  the  mine,  under  the  general 
conditions  of  this  particular  mine. 

Sample  No.  2,  containing  28.2%  moisture,  when  tested  in  a 
calorimeter,  showed  7574  B.T.U.  per  Ib.  The  average  B.T.U.  of 
the  three  samples,  when  a  portion  was  dried  at  104  to  107°C.  for  one 
hour,  was  11,003  per  Ib. 

Loss  by  Air  Drying. — A  portion  of  each  of  the  three  samples  was 
placed  in  a  tin  box,  open  at  the  top,  and  the  boxes  placed  in  the 
thermometer  and  hygrometer  house  of  the  meteorological  station  at 
the  University  of  Texas.  Each  sample  was  weighed  twice-  a  day  for 
several  days,  and  once  a  day  thereafter  for  nearly  two  weeks,  a  record 


COAL. 


53 


of  temperature  and  humidity  of  the   air   being   kept  by  means  of 
recording  instruments  placed  close  to  the  samples. 

The  lignite  which  was  exposed  in  the  three  samples  consisted  of 
lump  and  moderately  fine  material  which  was  intended  to  be  as  nearly 
as  possible  an  average  of  the  quality  of  the  coal  as  loaded  upon  the  cars. 
The  percentage  of  loss  of  each  of  the  samples  was  found  to  be  very 
nearly  the  same  as  on  the  remaining  lignite.  An  average  is  given  in 
the  following  table  of  the  loss  for  the  three  samples.  The  table 
also  gives  the  average  humidity  and  the  temperature  corresponding  for 
the  day  when  readings  -were  taken  and  the  percentage  of  loss  calcu- 
lated : 


No. 

Humidity. 

Temp.,°F. 

Loss,  % 

No. 

Humidity. 

Temp.,  °  F. 

Loss,  % 

1 

83 

75 

2.47 

7 

82 

75 

11.11 

2 

84 

77 

4.73 

8 

67 

71 

12.58 

3 

93 

68 

6.94 

9 

59 

67 

15.76 

4 

95 

66 

6.72 

10 

69 

69 

18.52 

5 

83 

70 

8.15 

11 

69 

67 

19.48 

6 

77 

74 

9.51 

12 

59 

63 

20.61 

The  table  shows  that  on  the  fourth  day  of  the  test  there  was  a 
slight  gain  in  moisture  over  that  of  the  day  previous,  but  this  is  due, 
without  doubt,  to  the  high  humidity,  the  average  being  95  for  that  day. 

After  exposure  to  the  air  for  twelve  days,  during  which  time  the 
average  loss  was  20.6%,  determinations  were  made  of  heat  values,  and 
an  average  of  9964  B.T.U.  per  pound  obtained. 

Mr.  Scott  concludes  that  the  loss  in  weight  of  lignite  in  transit 
is  due  largely,  if  not  entirely,  to  loss  of  moisture  by  air-drying,  and 
that  the  lignite  received  after  partial  air-drying  is  more  valuable 
than  when  it  was  loaded  at  the  mine. 

Ash. — The  composition  of  ash  approximates  to  that  of  fire-clay, 
with  the  addition  of  ferric  oxide,  sulphate  of  lime,  magnesia,  potash, 
and  phosphoric  acid. 

White-ash  coals  are  generally  freer  from  sulphur  than  the  red-ash 
coals,  which  contain  iron  pyrites,  but  there  are  exceptions  to  this  rule, 
as  in  a  coal  from  Peru  which  contains  more  than  10%  of  sulphur  and 
yields  not  a  small  percentage  of  white  ash.  In  it  the  sulphur  occurs 
in  organic  combination,  but  it  is  so  firmly  held  that  it  can  only  be 
partially  expelled,  even  by  exposure  to  a  very  high  heating  out  of 
contact  with  the  air. 

The  fusibility  of  ash  varies  according  to  its  composition.  It  is  the 
more  infusible  the  more  nearly  its  composition  approaches  to  fire-clay, 
or  silicate  of  alumina,  and  becomes  more  fusible  with  the  addition  of 


54  STEAM-BOILER  ECONOMY. 

other  substances,  such  as  iron,  lime,  etc.  Coals  high  in  sulphur 
usually  give  a  very  fusible  ash,  on  account  of  the  iron  with  which  the 
sulphur  is  in  combination.  A  fusible  ash  tends  to  form  clinker  upon 
the  grate-bars,  and  therefore  is  objectionable. 

The  amount  of  ash  in  coal  varies  greatly,  ranging  from  less  than  2 
per  cent  to  30  per  cent  or  more.  It  varies  with  the  district  in  which 
the  coal  is  mined,  with  individual  mines  of  the  district,  with  parts  of 
the  same  mine,  and  with  the  care  taken  in  mining.  With  anthracite 
coals  it  depends  on  the  size,  the  larger  sizes  having  the  least  ash. 

Analyses  of  Coal  Ash. — Complete  analyses  of  ash  of  58  samples 
of  Illinois  coal  are  given  by  Parr  and  Wheeler,  together  with  the 
volatile  inorganic  matter,  (carbon  dioxide  and  chlorine)  in  the  dry 
coal  which  is  not  found  in  the  ordinary  analysis  for  ash.  The  ash, 
found  by  the  usual  method,  ranged  from  7.53  to  16.25;  C02  in  the 
dry  coal  0  to  2.48 ;  01,  0  to  0.56  per  cent.  The  mineral  constituents 
of  the  ash,  as  obtained  by  high  fusion,  ranged  as  follows:  Si02,  22.8 
to  59.9;  Fe203,  3.1  to  52.3;  A1203,  3.2  to  31.5;  CaO,  1.9  to'34.0; 
MgO,  0  to  2.0. 

Heating  Value  of  Coal.— The  heating  value  of  different  varieties  of 
coal,  together  with  the  relation  of  the  heating  value  to  chemical  com- 
position, will  be  treated  at  length  in  the  chapter  on  Heating  Value  of 
Coal,  but  a  brief  statement  of  the  subject  is  given  below,  copied  from 
an  article  by  the  author  in  "Mines  and  Minerals,"  October,  1898. 

Coal  is  composed  of  four  different  things,  which  may  be  separated 
by  proximate  analysis,  viz.,  fixed  carbon,  volatile  hydrocarbon,  ash, 
and  moisture.  In  making  a  proximate  analysis  of  a  weighed  quantity, 
such  as  a  gram  of  coal,  the  moisture  is  first  driven  off  by  heating  it  to 
250°  or  280°  F.,  then  the  volatile  matter  is  driven  off  by  heating  it  in 
a  closed  crucible  to  a  red  heat,  then  the  carbon  is  burned  out  of  the 
remaining  coke  to  a  white  heat,  with  sufficient  air  supply,  until 
nothing  is  left  but  the  ash. 

The  fixed  carbon  has  a  constant  heating  value  of  about  14,600 
B.T.U.  per  Ib.  The  value  of  the  volatile  hydrocarbon  depends  on  its 
composition,  and  that  depends  chiefly  on  the  district  in  which  the 
coal  is  mined.  It  may  be  as  high  as  21,000  B.T.U.  per  Ib.,  or  about 
the  heating  value  of  marsh-gas,  in  the  best  semi-bituminous  coals, 
which  contain  very  small  percentages  of  oxygen,  or  as  low  as  10,000 
B.T.U.  per  Ib.,  as  in  those  from  some  of  the  Western  States,  which  are 
high  in  oxygen.  The  ash  has  no  heating  value,  and  the  moisture  has 
in  effect  less  than  none,  for  its  evaporation  and  the  superheating  of 


COAL. 


55 


the  steam  made  from  it  to  the  temperature  of  the  chimney-gases 
absorb  some  of  the  heat  generated  by  the  combustion  of  the  fixed  car- 
bon and  volatile  matter. 

The  analysis  of  a  coal  may  be  reported  in  three  different  forms,  as 
percentages  of  the  moist  coal,  of  the  dry  coal,  or  of  the  combustible. 
Thus,  suppose  one  gram  of  coal  is  analyzed,  and  the  first  heating 
shows  a  loss  of  weight  of  0.1  gram,  the  second  of  0.3  gram,  the  third 
0,5  gram,  the  remainder,  or  ash,  weighing  0.1  gram,  the  complete 
report  would  be  as  follows : 


Per  Cent  of  the 
Moist  Coal. 

Per  Cent  of  the 
Dry  Coal. 

Per  Cent  of  the 
Combustible. 

Moisture  
Volatile  matter  
Fixed  carbon  
Ash 

10 
30 
50 
10 

33.33 

55.56 

11.11 

37.50 
62.50 

100 

100.00 

100.00 

The  relation  of  the  volatile  matter  and  of  the  fixed  carbon  in  the 
last  column  of  the  table  enables  us 'to  judge  the  class  to  which  the 
coal  belongs,  as  anthracite,  semi-anthracite,  semi-bituminous,  bitu- 
minous, or  lignite.  Coals  containing  less  than  10  per  cent  volatile 
matter  in  the  combustible  would  be  classed  as  anthracite,  between  10 
and  15  per  cent  as  semi-anthracite,  between  15  and  30  per  cent  as 
semi-bituminous,  between  30  and  50  per  cent  as  bituminous,  and  over 
50  per  cent  as  lignitic  coals  or  lignites. 

The  figures  in  the  second  column,  representing  the  percentages  in 
the  dry  coal,  are  useful  in  comparing  different  lots  of  coal  of  one  class, 
and  they  are  better  for  this  purpose  than  the  figures  in  the  first  column, 
for  the  moisture  is  a  variable  constituent,  depending  to  a  large  extent 
on  the  weather  to  which  the  coal  has  been  subjected  since  it  was  mined, 
on  the  amount  of  moisture  in  the  atmosphere  at  the  time  when  it  is 
analyzed,  and  on  the  extent  to  which  it  may  have  accidentally  been 
dried  during  the  process  of  sampling. 

The  heating  value  of  a  coal  depends  on  its  percentage  of  total  com- 
bustible matter,  and  on  the  heating  value  per  pound  of  that  combus- 
tible. The  latter  differs  in  different  districts  and  bears  a  relation  to 
the  percentage  of  volatile  matter.  It  is  highest  in  the  semi -bituminous 
coals,  being  nearly  constant  at  about  15,750  B.T.IL  per  Ib.  It  is 
between  14,800  and  15,500  B.T.U.  in  anthracite,  and  ranges  from 


56 


STEAM-BOILER  ECONOMY. 


15,500  down  to  13,000  or  less  in  the  bituminous  coals,  decreasing 
usually  as  we  go  westward,  and  as  the  volatile  matter  contains  an 
increasing  percentage  of  oxygen. 

In  1892  the  author  deduced  from  Mahler's  tests  on  European  coals 
a  table  of  the  approximate  heating  value  of  coals  of  different  com- 
position, which  is  given,  somewhat  modified,  below.  (Trans.  A.  S. 
M.  E.,  vol.  xx.  p.  337.) 

APPROXIMATE   HEATING   VALUE   OP   COALS.* 


Per  Cent 

Heating  Value  per  Lb. 

Per  Cent 

Heating  Value  per  Lb. 

Volatile   Matter 

Combustible. 

Volatile  Matter 

Combustible. 

in  Coal 

in  Coal 

Dry  and  Free 

Dry  and  Free 

from  Ash. 

B.T.U. 

Calories. 

from  Ash. 

B.T.U. 

Calories. 

0 

14,580 

8,100 

32 

15,480 

8,600 

3 

14,940 

8,300 

37 

15,120 

8,400 

6 

15,210 

8,450 

40 

14,760 

8,200 

10 

15,480 

8,600 

43 

14,220 

7,900 

13 

15,660 

8,700 

45 

13,860 

7,700 

20 

15,840 

8,800 

47 

13,320 

7,400 

28 

15,660 

8,700 

49 

12,420 

6,900 

*  See  the  curve  plotted  from  these  figures  on  page  159. 


The  experiments  of  Lord  and  Haas  on  American  coals  (Trans, 
Am.  Inst.  Mining  Engineers,  1897)  practically  confirm  these  figures 
for  all  coals  in  which  the  percentage  of  volatile  matter  is  less  than 
40%  of  the  combustible,  but  for  coals  containing  less  than  60%  fixed 
carbon  or  more  than  40%  volatile  matter  in  the  combustible  they  are 
liable  to  an  error  in  either  direction  of  about  4%.  It  appears  from 
these  experiments  that  the  coal  of  one  seam  in  a  given  district,  where 
the  ratio  of  the  volatile  matter  to  the  total  combustible  is  uniform,  has 
the  same  heating  value  per  pound  of  combustible,  within  one  or  two 
per  cent,  but  that  coals  of  the  same  proximate  analysis,  and  containing 
over  40%  volatile  matter,  but  mined  in  different  districts,  may  differ 
6  or  8  per  cent  in  heating  value. 

It  will  be  noticed  that  the  coals  containing  from  13  to  28  per  cent 
of  volatile  matter  in  the  combustible  have  practically  the  same  heating 
value.  This  is  confirmed  by  Lord  and  Haas's  tests  of  Pocahontas  coal. 
A  study  of  these  tests  and  of  Mahler's  indicates  that  the  heating  value 
of  all  the  semi-bituminous  coals,  15  to  30  per  cent  volatile  matter,  is 
within  1J%  of  15,750  B.T.U.  per  Ib. 

The  heating  value  of  any  coal  may  also  be  calculated  from  its  ulti- 


COAL.  57 

mate  analysis,  with  a  probable  error  not  exceeding  2%  (except  in  the 
cases  of  cannel-coal  and  some  lignites,  in  which  the  error  may  be 
greater)  by  the  following  formula : 

Heating  value  per  Ib.  =  146C  +  620  TH  -  -Y 

in  which  C,  H,  and  0  are  respectively  the  percentages  of  carbon, 
hydrogen,  and  oxygen.  This  formula  is  known  as  Dulong's.  Its  ap- 
proximate accuracy  is  proved  by  both  Mahler's  and  Lord  and  Haas's 
experiments,  and  any  deviation  of  the  calorimetric  determination  of 
any  ordinary  coal  more  than  2%  from  that  calculated  by  the 
formula  is  more  likely  to  proceed  from  an  error  in  either  the  calo- 
rimetric test  or  the  analysis  than  from  an  error  in  the  formula. 

Genital's  Formula. — E.  Goutal,  in  Co'mptes  Rendus,  Sept.,  1902, 
gives  a  formula  which  is  frequently  quoted  by  other  writers,  in 
English  units,  as  follows :  B.T.U.  =  14,760  C  +  aV,  in  which  C 
is  the  fixed  carbon  and  V  the  volatile  matter  in  1  Ib.  of  combustible, 
and  a  a  coefficient  taken  from  a  table.  (See  Gebhardt's  Power  Plant 
Engineering.)  The  values  obtained  by  this  formula  agree  fairly  well 
with  those  given  in  the  author's  table  for  coals  in  which  the  volatile 
matter  is  not  in  excess  of  30%  of  the  combustible;  beyond  that  they 
vary  considerably.  It  is  evident  that  it  is  easier  to  take  the  B.T.U. 
directly  from  a  table  than  to  find  the  value  of  a  in  a  table  and  then 
to  make  the  computation  from  a  formula. 

W.  Inchley  (The  Engineer,  Feb.  17,  1911),  gives  a  formula  which 
he  considers  better  than  Dulong's  for  steam  coal,  viz. : 

Calorific  value  =    8,OOOC  +  33,830H  calories  per  gram. 
=  14,4000  +  60,890H  B.T.U.  per  Ib. 

It  is  evident,  since  his  formula  contains  no  factor  for  oxygen,  that 
it  cannot  give  correct  results  for  coals  high  in  oxygen.  Testing  it 
by  the  average  figures  given  by  Lord  and  Haas  for  Pocahontas  and 
Hocking  Valley  coals  (see  pages  156  and  157)  we  find  the  following: 


By  Calorimeter 

Dulong 

Inchley. 

Pocahontas  . 

8176 

8198 

8241 

Hocking  Valley  

6663 

6683 

6892 

Errors  in  Reported  Heating  Values  of  Coals. — Errors  in  sampling 
and  in  the  calorimetric  test  are  quite  common,  and  the  error  of  the 
latter  is  almost  always  in  the  direction  of  making  the  reported,  heat- 


58  STEAM-BOILER  ECONOMY. 

ing  value  of  a  coal  too  small.  The  effect  of  this  error  is  to  make  the 
apparent  efficiency  of  a  boiler  tested  with  this  coal  higher  than  the  real 
efficiency.  Whenever  the  efficiency  reported  is  high  and  at  the  same 
time  the  reported  heating  value  of  the  fuel  per  pound  of  combustible  is 
more  than  2  per  cent  lower  than  the  average  figures  in  published  tables 
for  coal  from  the  same  district,  the  results  should  be  looked  on  with 
suspicion.  Further  information  on  this  subject  will  be  found  in  a 
paper  by  the  author  entitled  "The  Efficiency  of  a  Steam-boiler :  What 
is  it  ?"  in  Trans.  Am.  Soc.  Mechanical  Engineers,  vol.  xvii,  p.  645. 

New  Classification,  and  Tables  of  Heating  Value.*— The  recent 
publication  by  the  United  States  Bureau  of  Mines  in  Bulletin  No.  22 
of  over  3000  analyses  and  results  of  calorimetric  examinations  of 
American  coals  offers  the  best  opportunity  that  has  ever  been  had 
for  a  study  of  the  long-mooted  questions  of  the  classifications  of  coals 
and  of  the  relation  of  their  chemical  composition  to  their  heating 
value. 

The  writer  has  made  a  selection  of  155  analyses  of  coals  from 
different  states,  showing  practically  the  extreme  range  of  composition 
of  heating  value  of  the  coals  of  each  of  these  states,  whenever  a  suf- 
ficient number  of  coals  of  such  states  are  given  in  the  bulletin.  The 
most  important  items  of  the  ultimate  and  proximate  analyses  were 
tabulated,  viz.,  the  S,  H,  C,  0,  and  N  of  the  ultimate  analysis  as  re- 
ferred to  the  combustible  (coal  free  of  moisture  and  ash),  also  the 
volatile  matter,  the  moisture  and  the  ash  of  the  proximate  analysis, 
the  moisture  and  ash  being  referred  to  the  coal  as  received,  and  the 
volatile  matter  being  referred  to  the  combustible.  (See  Table  I.) 
The  fixed  carbon  referred  to  combustible  is  100  per  cent  minus  the 
volatile  matter  of  the  combustible,  and  referred  to  coal  as  received 
it  is  100  per  cent  minus  the  sum  of  moisture  ash  and  volatile  matter. 
The  results  as  given  in  the  bulletin  were  calculated  to  three  different 
bases:  (1)  as  received,  (2)  dry  coal,  (3)  ash  and  moisture  free 
(commonly  called  combustible) ;  and  in  many  cases  to  a  fourth  basis, 
ash,  moisture,  and  sulphur-free.  For  the  purpose  of  comparison, 
however,  other  information  was  desired,  such  as  the  B.T.IJ.  per  Ib. 
of  coal  air-dry,  ash-free,  and  air-dry,  ash-  and  sulphur-free,  not  con- 
tained in  the  bulletin.  The  writer  has  calculated  and  tabulated  these 
omitted  items,  but  it  should  be  stated  that  the  figures  which  he  ob- 

*  Abstract  of  a  paper  presented  by  the  author  at  the  June,  1914,  meeting 
of  the  American  Society  of  Mechanical  Engineers. 


COAL. 


59 


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tained  relating  to  B.T.U.  calculated  to  the  sulphur-free  basis,  are 
probably  too  high  in  many  cases  of  high  sulphur  coals. 

Having  thus  tabulated  the  results,  the  questions  to  be  solved 
are  (1)  how  shall  the  coals  be  classified;  (2)  what  relation  does  the 
heating  value  of  the  coals  bear  to  the  chemical  composition. 

In  studying  the  155  coals,  the  writer  first  plotted  the  B.T.U. 
per  Ib.  combustible  with  the  results  which  are  shown  graphically  in 
Fig.  2.  This  plotting  shows  that  all  the  coals  of  the  Appalachian 
field  come  close  to  the  original  curve  drawn  by  the  writer  in  1892 
from  Mahler's  tests  of  European  coals,  when  the  volatile  matter  in 
the  combustible  is  35  per  cent  or  less.  For  coals  higher  in  volatile 
matter,  and  for  Western  coals  generally,  the  heating  value  varies  over 
a  wide  range  and  appears  to  have  no  relation  to  the  volatile  matter, 
but  each  district  has  a  law  of  its  own.  The  Illinois  coals  are  all  found 
within  the  small  area  shown  by  dotted  lines.  Perhaps  the  most  im- 
portant conclusion  from  Fig.  2  is  that  all  the  semi-bituminous  coals 
of  the  Eastern  states,  and  those  from  the  Western  states  and  Alaska 
with  a  very  few  exceptions,  have  a  heating  value  per  pound  of  com- 
bustible that  is  very  close  to  15,750  B.T.U.  With  bituminous  coals 
and  lignite  containing  over  36  per  cent  of  volatile  matter  in  the 
combustible  there  appears  to  be  no  law  connecting  the  heating  value 
with  the  percentage  of  volatile  matter,  and  the  plotting  is  not  con- 
tinued beyond  44  per  cent. 

As  many  of  the  coals  high  in  volatile  matter  are  also  high  in 
sulphur,  it  was  attempted  to  find  if  high  sulphur  was  the  cause  of 
some  of  the  variation  of  the  heating  value,  but  the  results  are  nega- 
tive. When  the  heating  value  per  pound  of  combustible  is  converted 
for  sulphur  by  the  usual  method,  by  subtracting  4050  B.T.U.  per  Ib. 
S,  and  dividing  by  1  minus  (%  S-^-100),  the  value  thus  found  is 
often  far  higher  than  the  heating  value  per  pound  of  combustible  of 
coals  of  the  same  districts  that  are  low  in  sulphur.  Lower  values 
for  these  coals  might  be  found  if  they  were  converted  by  the  "unit 
coal"  method  of  Parr  and  Wheeler  (Bulletin  37,  1909,  of  the  Illinois 
University  Engineering  Experiment  Station),  viz.: 

Indicated  dry  B.T.U.  -  5000S 
B.T.U.  per  Ib.  unit  coal  .        I.QQ  -  (1.08  ash  +  0.55S)       ' 

Fig.  3  shows  the  result  of  plotting  the  heating  value  per  pound 
of  air-dry  coal  and  ash-  and  sulphur-free,  against  the  percentage  of 


COAL. 


61 


62  STEAM-BOILER  ECONOMY. 

moisture  in  such  coal,  for  those  cases  in  which  the  moisture  does  not 
exceed  11  per  cent.  The  results  indicate  that  this  method  may  prove 
to  be  of  considerable  importance  when  it  is  applied  separately  to  the 
coals  of  different  states  or  districts,  especially  the  bituminous  coals 
of  the  Middle  West.  The  high  position  of  the  Kansas  coals  and  of 
one  of  the  Missouri  coals  may  be  due  to  the  error  of  the  common 
method  of  correcting  for  sulphur. 

The  average  results  shown  in  Fig.  3  correspond  approximately 
to  the  following  formula. 

B.T.U.  per  Ib.  air-dry  coal,  ash-free  =  16,400  -  800Mfl,  for  semi- 
bituminous  coal; 

=  15,300  -  240Ma,   for    bitu- 
minous coal ; 

in  which  Ma  is  the  percentage  of  moisture  remaining  in  the  coal  after 
air-drying,  referred  to  the  coal  free  from  ash.  That  is, 

M~L 


100-(A+L)' 

in  which  M  and  A  are  respectively  the  moisture  and  ash  in  the  coal 
as  received,  and  L  is  the  loss  on  air-drying,  figured  as  a  percentage  of 
the  coal  as  received. 

After  studying  the  coals  by  the  method  of  plotting  as  described, 
Table  2  was  constructed,  in  which  a  revised  classification  is  attempted. 
The  extreme  differences  in  B.T.U.  per  Ib.  between  the  B.T.U.  per 
Ib.  given  and  those  that  result  from  calculation  by  Dulong  's  formula, 
by  the  Mahler  curve,  and  by  the  moisture  formulae  for  air-dry,  ash-free 
coal,  are  given  in  the  table  on  page  73.  The  extent  of  these  differ- 
ences suggests  that  in  some  cases  the  calorimetric  determinations,  or 
the  analyses,  or  both,  may  be  in  error,  and  indicates  the  necessity  for 
thoroughly  checking  the  loss  in  air-drying,  the  moisture  determina- 
tions of  the  air-dried  coal,  the  analyses,  proximate  and  ultimate,  and 
the  calorimetric  work. 


63 


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70 


STEAM-BOILER  ECONOMY. 


TABLE   II. 

CLASSIFIED    LIST   OF    COALS 


Combustible. 

Air-dry,  Ash-free. 

Vol. 

S. 

O. 

B.T.U. 

Moist. 

B.T.U. 

I.  ANTHRACITE 
Alaska  4  
Colo  5... 

8.8 
3.6 
1.3 
3.7 

8.5 

14.8 
10.0 
13.1 

28.8 
27.9 
15.5 
16.7 
17.0 
20.7 
23.8 
25.8 
19.4 
16.5 
16.0 
19.7 
17.5 
18.3 
21.7 
15.7 
19.0 
24.8 
25.0 
19.5 
17.3 
17.2 
19.0 
17.5 
16.3 
25.3 
23.3 
21.8 
19.9 
16.5 
18.1 

55.5 
57.0 
47.4 
67.6 

33.4 
35.3 
31.3 
33.7 
40.0 
39.8 
39.5 
35.3 
41.5 
34.4 

0.73 
0.87 
1.00 
0.68 
0.72 

2.33 
0.74 
0.82 

0.59 
1.58 
1.29 
3.16 
3.57 
1.47 
0.58 
0.72 
1.55 
1.13 
1.02 
0.94 
0.98 
0.96 
1.15 
1.36 
1.87 
1.81 
1.50 
1.73 
1.63 
5.09 
0.68 
0.68 
0.48 
0.86 
0.61 
1.27 
0.60 
0.79 
0.86 

1.38 
1.15 
0.92 
2.32 

1.13 
1.07 
0.72 
0.56 
2.82 
6.68 
4.93 
0.58 
0.74 
0.96 

4.04 
1.32 
2.13 
2.41 
2.67 

2.57 

2.17 
4.18 

4.45 
3.42 
3.02 
1.69 
1.25 
4.27 
4.34 
2.29 
5.96 
2.81 
2.54 
3.01 
2.47 
2.93 
2.87 
1.87 
3.32 
5.50 
3.72 
1.99 
2.82 
1.66 
3.42 
2.23 
3.97 
4.13 
1.68 
5.52 
2.80 
4.56 
1.97 

7.57 

7.61 
5.34 
13.68 

6.99 
7.00 
9.38 
8.77 
9.74 
5.26 
7.27 
8.05 
8.79 
6.93 

15,203 
15,413 
14,882 
15,248 
15,410 

15,496 
15,457 
15,500 

15,757 
15,620 
15,651 
15,624 
15,530 
15,602 
15,849 
15,939 
15,653 
15,710 
15,640 
15,826 
15,856 
15,721 
15,586 
15,728 
15,840 
15,376 
15,660 
15,683 
15,847 
15,493 
15,840 
15,910 
15,264 
15,399 
15,736 
15,781 
16,038 
15,820 
15,919 

15,800 
16,013 
16,176 
14,918 

15,590 
15,214 
14,681 
15,559 
14,818 
15,167 
14,809 
15,328 
14,875 
15,221 

1.55 

1.08 
1.43 
0.83 
0.80 

1.45 
0.91 
0.90 

1.15 

0.94 
0.60 
0.86 
0.92 
1.34 
0.83 
1.43 
0.74 
0.90 
1.10 
0.80 
0.66 
0.61 
0.53 
0.70 
0.99 
0.40 
0.86 
1.50 
0.65 
0.76 
0.54 
0.64 
1.67 
1.18 
0.90 
0.81 
0.69 
0.65 
0.73 

0.92 
1.44 
0.84 
8.26 

1.23 
1.77 
1.01 
0.87 
2.34 
2.86 
2.49 
1.64 
1.64 
0.80 

14,968 
15,247 
14,666 
15,123 
15,367 

15,272- 
15,398 
15,439. 

*. 

15,577 
15,475 
15,559 
15,525 
15,387 
15,393 
15,716 
15,712 
15,540 
15,577 
15,478 
15,699 
15,746 
15,625 
15,504 
15,619 
15,680 
15,316 
15,523 
15,624 
15,744 
15,378 
15,750 
15,795 
15,013 
15,218 
15,597 
15,655 
15,998 
15,804 
15,802 

15,6461 
15,784 
16,042  1 
13,686 

15,400 
14,947 
14,533 
15,423 
14,470 
14,734 
14,436 
15,095 
14,630 
15,099 

Pa  7 

Pa                              8 

Wash  ...                     5 

II.  SEMI-ANTHRACITE 
Ark.  .                           1 

Pa..  .                     .  .11 

Va.                             3 

III.  SEMI-BITUMINOUS 
Ala                             1 

Ala                             2 

Alaska  3  
Ark.    .                         2 

Ark  5 

Ark                              6 

Colo  7 

Colo           .                8 

Ga                              1 

Md...                     .  .1. 

Md                             2 

Md  3 

Md           .                  4 

Mont  9  .  . 
Okla                            2 

Okla  3  
Pa  2  
Pa.  .  .                           3 

Pa  4  . 

Pa.            .                   6 

Pa  9  
Pa                             10 

Va  4 

Va.  .  .                       .  .  5  .  .  . 

Wash  6  
W.  Va.  .                 .    2.  . 

W.  Va    .                    3 

W.  Va  4.    . 

W.  Va  7.  . 
W.  Va  8  
W   Va                       10 

IV.  CANNEL* 
Ky                                2 

Ky  3  
W.  Va.  .                  .  .1.  . 

Utah  6  

V.  BITUMINOUS,  HIGH-GRADE 
Ala                             3 

Ala  :  4.  . 
Colo                            4 

Colo  6.  .  . 
Ill                                 6 

Kan  2 

Kan                             4 

Ky  4  
N    Mex                        1 

N.  Mex  2  

*  H  in  combustible:  Ky.  2,  7.13;  Ky.  3,  7.  46;  W.  Va.  1,7.13;  Utah,  6.7.73.  The  highes 
H  in  the  other  coals  is  5.78,  Mo.  6.  The  figures  in  the  first  column  are  the  order  of  the  coala 
of  the  several  States  in  Table  I. 


COAL. 


71 


TABLE  II— (Continued) 


Combustible. 

Air-dry,  Ash-free. 

Vol. 

S. 

O. 

B.T.U. 

Moist. 

B.T.U. 

V.  BITUMINOUS  HIGH-GRADE 
(Continued). 
Ohio                        .  .  1  

45.5 
42.9 
42.8 
35.5 
40.8 
38.3 
32.4 
38.4 
33.8 
39.8 
38.3 
40.2 
35.3 
44.0 
44.3 
40.0 
36.4 
39.3 

37.7 
44.2 
53.8 
41.4 
37.4 
39.3 
40.9 
47.3 
51.2 
40.6 
44.2 
39.8 
44.0 
43.5 
38.8 
37.1 
44.8 
44.6 
50.8 
45.3 
50.2 
34.3 
39.6 
44.3 
37.8 
47.7 
41.7 
45.6 
47.2 
41.8 
39.6 

40.8 
46.0 
40.8 
46.2 
42.2 
44.8 
47.5 
47.3 
33.3 
44.4 
43.7 

4.58 
3.97 
3.66 
7.36 
2.06 
1.38 
1.00 
1.17 
0.95 
5.73 
1.32 
0.85 
0.97 
5.23 
3.86 
0.72 
0.73 
0.99 

.37 
.83 
.80 
.36 
.14 
3.10 
2.88 
6.60 
8.53 
6.64 
9.94 
5.22 
4.29 
5.64 
1.53 
1.11 
5.16 
4.96 
6.33 
9.45 
6.21 
4.86 
0.60 
0.68 
0.63 
5.74 
2.31 
0.60 
0.62 
0.57 
0.84 

0.94 
6.33 
5.55 
6.02 
1.78 
6.73 
5.69 
4.85 
12.99 
1.72 
2.00 

8.10 
7.04 
9.01 
3.71 
7.35 
6.94 
7.35 
7.94 
6.70 
5.14 
8.01 
12.18 
5.65 
13.93 
7.06 
10.10 
5.14 
11.40 

10.45 
14.11 
11.47 
12.02 
8.46 
9.03 
9.50 
9.96 
8.96 
8.03 
5.64 
5.98 
8.90 
7.46 
9.54 
10.51 
9.53 
11.83 
7.73 
6.28 
6.12 
9.50 
9.77 
12.70 
11.58 
9.44 
9.26 
13.30 
10.93 
12.38 
9.25 

18.83 
10.53 
12.02 
10.09 
10.55 
9.69 
9.73 
10.68 
6.82 
20.44 
15.87 

14,888 
14,965 
14,832 
15,025 
15,061 
15,345 
15,511 
14,960 
15,320 
15,125 
15,156 
14,918 
15,291 
14,796 
15,291 
15,107 
15,448 
14,848 

14,467 
13,838 
14,336 
14,492 
14,621 
14,724 
14,492 
14,305 
14,206 
14,555 
14,724 
14,922 
14,657 
14,836 
14,499 
14,603 
14,351 
13,892 
14,679 
14,476 
15,134 
14,134 
14,681 
14,539 
14,269 
14,332 
14,711 
14,245 
14,764 
14,348 
14,793 

12,964 
14,263 
13,921 
14,155 
14,746 
14,089 
14,305 
14,202 
13,693 
13,338 
13,162 

1.75 
2.38 
3.83 
1.38 
1.57 
1.42 
1.07 
1.97 
1.08 
1.32 
1.79 
2.52 
1.49 
1.55 
1.58 
2.11 
1.36 
2.13 

2.69 
2.55 
5.19 
5.15 
6.02 
3.71 
5.48 
5.01 
5.35 
6.24 
4.09 
4.30 
6.52 
2.98 
4.70 
5.59 
4.65 
3.42 
3.69 
2.83 
5.68 
2.42 
2.30 
3.06 
4.69 
3.30 
4.31 
4.98 
2.47 
3.26 
2.73 

5.42 
6.75 
6.02 
10.59 
9.60 
6.17 
11.33 
7.37 
2.37 
8.75 
6.34 

14,626 
14,642 
14,431 
14,814 
14,825 
15,127 
15,346 
14,665 
15,137 
14,921 
14.887 
14,381 
15,069 
14,569 
15,048 
14,787 
15,237 
14,552 

14,078 
13,484 
13,593 
13,745 
13,742 
14,177 
13,698 
13,576 
13,445 
13,647 
14,121 
14,269 
13,702 
14,394 
13,818 
13,786 
13,682 
13,416 
14,136 
13,921 
14,276 
13,791 
14,342 
14,093 
14,152 
13,523 
14.075 
13,536 
14,399 
13,879 
14,391 

12,261 
13,300 
13,084 
12,657 
13,329 
13,220 
12,684 
13,156 
13,368 
12,170* 
12,324* 

Ohio                            4 

Ohio                    ...  .5  

Okla                            5 

Okla  6  

Pa                                1          ... 

Pa  5  

Tenn                        .    1    

Tenn                           2 

Tenn                            3 

Va                                1 

Va                               2 

Va  6  

Wash                          3      

W.  Va.  .                 .  .5.  .  . 

W.  Va                         6   . 

W.  Va  9  

Wyo.  .                        .8        

VI.  BITUMINOUS  MEDIUM 
GRADE 
Ala.  .  .                 5  
Alaska  1  
Cal  2  
Ill                                  2               .  . 

111..                         ..3... 

Ill                                7 

Ind  1  

Ind.                             3      

la.  .                         .  .2.  .  , 

la  3  
Kan  .  .                     .  .  1  .  . 

Kan                             3  

Ky.  .                       ..!.. 

Ky  5  
Mich                             1 

Mich  2  

Mo                               1 

Mo  3  
Mo                              4 

Mo  5  

Mo                              6 

Mont  5  

Mont                          8          ... 

N.  Mex  3  
Ohio  2.  
Ohio                            3 

Okla  4  
Utah                            1 

Utah  2  
Wash                          1 

Wyo  9  

VII.  BITUMINOUS  Low  GRADE 
Alaska  2  

Ill                                 1  

Ill                                4 

111  .  .                       .  .  .  5  
Ind..  .                     .  .2  

Ind  4  
la                                 1        

Mo  2  
Mont                            1  

Mont  -                         2          ... 

Mont                  .    .  .  3  

*  Montana  2  and  3  are  classed  aa  sub-bituminoua  by  the  Bureau  of  Mines. 


72 


STEAM-BOILER  ECONOMY. 
TABLE  II— (Continued) 


Combustible. 

Air-dry,  Ash-free. 

Vol. 

S. 

O. 

B.T.U. 

Moist. 

B.T.U. 

VII.  BITUMINOUS  Low  GRADE 
(Continued) 
Mont  4  
Mont  6  
N.  Mex.  .                .  .4.  . 

37.5 
32.6 
42.8 
46.8 
45.9 
48.1 
38.4 
45.4 
44.0 
47.5 

52.1 
53.5 
41.4 
45.5 
41.1 
69.0 
54.1 
49.8 
56.7 
45.9 
44.0 
47.0 
40.0 
59.6 
70.9 
45.3 
49.6 
46.6 
54.6 
27.8 
44.3 
39.3 
59.9 
47.5 
43.5 
50.6 
49.4 

6.6 
6.3 
21.7 
21.0 
50.9 

0.86 
2.88 
0.78 
2.38 
5.93 
1.65 
0.56 
7.27. 
7.10 
0.44 

0.96 
4.62 
0.44 
0.51 
0.39 
1.86 
0.67 
1.16 
2.04 
0.86 
1.15 
5.52 
0.68 
1.46 
1.00 
1.61 
0.90 
4.88 
0.53 
1.09 
0.36 
0.17 
1.18 
4.04 
0.72 
2.17 
0.77 

0.05 
0.09 
10.76 
1.43 
4.77 

16.21 
16.14 
14.00 
15.69 
10.62 

is^is 

10.05 
14.18 
17.11 

21.17 
16.79 
16.97 
16.52 
18.00 
23.47 
26.64 

13,865 
12,438 
13,939 
13,322 
13,667 
14,618 
13,118 
13,586 
13,081 
13,423 

12,497 
12,890 
11,619 
13,239 
12,746 
11,900 
10,211 
11,398 
12,557 
12,101 
12,769 
11,493 
12,098 
13,043 
10,811 
12,890 
12,452 
11,264 
12,226 
12,956 
11,722 
12,683 
11,194 
12,447 
11,030 
9,630 
10,141 

13,120 
14,002 
13,945 
14,945 
16,457 

7.58 
8.09 
11.70 
7.87 
7.74 
11.88 
5.60 
9.65 
11.47 
6.56 

22.00 
10.95 
8.21 
15.35 
8.68 
15.55 
25.02 
13.93 
26.20 
11.66 
10.16 
7.05 
15.77 
15.73 
23.58 
11.02 
11.82 
15.35 
17.21 
9.56 
9.75 
12.54 
24.09 
18.84 
7.55 
22.69 
14.85 

1.26 
0.52 
4.77 
1.77 
16.42 

12,813 
11,432 
12,309* 
12,008* 
12,609 
12,882 
12,384 
12,276 
11,374 
12,548 

9,750 
11,478 
10,664 
10,094 
11,638 
10,143 
7,656 
9,801 
8,886 
10,885 
11,471 
10,684 
10,189 
11,077 
10,169 
11,578 
11,036 
9,535 
10,122 
11,573 
10,581 
11,093 
8,496 
10,103 
10,198 
7,458 
8,666 

12,955 
13,930 
13,279 
14,722 
13,757 

N.  Mex  5  
Okla  1  

Ore.  ...                       3 

Utah.  .  .                   .  .  3  .  . 
Utah  4  
Utah  5  
Wash                          2 

VIII.  SUB-BITUMINOUS  AND 
LIGNITE 
Ark.  .  .                    .  .  3  .  . 
Cal  .  .                       .  .  1  .  . 

Colo                             1 

Colo  2  
Colo                            3 

Mont  7  
Mont  10  

N.  Dak  1  
N   Dak                       2 

17.69 
22.67 
19.68 

'18:99' 

'isiee' 

20.54 
22.14 
22.06 
10.94 
24.35 
21.95 
23.41 
17.06 
25.54 
29.86 
33.14 

5.59 

3.27 
5.28 
6.44 

N.  Dak.  .  .                 3 

Ore  1  ... 

Ore.  .                            2 

S.  Dak  1  
Tex.    .                         1 

Tex  2  . 

Tex  3  

Tex  4  
Utah  7  
Wash  4  
Wyo  1  
Wyo                             2 

Wyo  3  .  . 
Wyo                             4 

Wyo  .5.  . 
Wyo                               6 

Wyo  .  .  7  .  . 
Wyo                           10 

NOT  CLASSIFIED 
R.  I  1  
R.  I  2  
Alaska  5  
Ark  4  
Idaho  1  

*  New  Mexico  4  and  5  are  classed  as  sub-bituminous  by  the  Bureau  of  Mines. 

Wyoming  6,  Sample  taken  10  ft.  from  entrance,  coal  very  much  weathered;  Wyoming  7. 
Surface  exposure;  Wyoming  10,  Shallow  prospect  pit;  coal  badly  weathered. 

The  Rhode  Island  coals  are  graphitic  and  are  not  used  as  fuel.  Alaska  5  and  Arkansas  4 
may  be  classed  as  semi-bituminous  by  their  percentage  of  volatile  matter,  but  they  are  higher 
in  oxygen  and  in  moisture,  and  lower  in  heating  value  than  other  semi-bituminous  coals. 
The  Idaho  coal  is  apparently  a  cannel  coal  very  high  in  moisture,  but  the  ultimate  analysis 
is  lacking. 

Differences  between  Actual  and  Calculated  Heating  Values. — The 

following  table  shows  the  range  of  variation  of  heating  value  as  deter- 
mined by  calorimeter  from  that  found  by  estimation  from  the  Dulong 
formula,  the  Mahler  curve  and  the  moisture  formula. 


COAL. 


73 


RANGE    OF    VARIATION   OF    HEATING    VALUES. 


Plaofl 

B.T.U.  greater 

+)  or  less  (-)  tha 

n  estimated  by 

Dulong  Formula. 

Mahler  Curve. 

Moisture  Formula. 

I.  Anthracite  
II.  Semi-anthracite  

-   164  to  +  127 
21  to  -  193 

-     76  to  +373 
-     23  to  -  176 

-  385  to  +  87 
—  233  to  274 

III.  Semi-bituminous  
IV    Cannel 

-  674  to  +  546 
-  284  to  +  172 

-  516  to  +208 

-  557  to  +64H 

_]_  1Q«  to  -1-68  i 

V.  Bituminous,  high  grade 
VI.  Bituminous,  medium  g. 
VII.  Bituminous,  low  grade. 

-  344  to  +  842 
-  673  to  +  592 
-  309  to  +1293 

-  849  to  +725 
-1226  to  +736 

-  447  to  +906 
-  923  to  +967 
—  1674  to  +680 

VIII.  Sub-bituminous     and 
lignite  

-1397  to  +1292 

For  the  first  five  classes  the  maximum  variation  of  the  calorimetric 
from  the  estimated  value  by  the  Dulong  formula  is  842  B.T.U.,  by 
the  Mahler  curve  849,  and  by  the  moisture  formula  908.  The  revised 
classification  is  as  follows: 

CLASSIFICATION   OF    COALS. 


Volatile 

Moisture 

B.T.U. 

Matter 
Per  Cent 
of  Com- 
bustible. 

Oxygen 
in  Com- 
bustible 
Per  Cent. 

in  Air  Dry 
Coal  Free 
from  Ash. 
Per  Cent. 

B.T.U. 
per  Ib. 
Combustible. 

per  Ib. 
Coal  Air 
Dry,  Ash 
Free. 

I.  Anthracite  

less  than  10 

1  to    4 

less  than  1  .  8 

14,800  to  15,400 

14,600  to  15,400 

II.  Semi-anthracite. 

10  to  15 

1  to    5 

less  than  1  .  8 

15,400  to  15,500 

15,200  to  15,500 

III.  Semi-bituminous 

15  to  30 

1  to    6 

less  than  1  .  8 

15,400  to  16,050 

15,300  to  16,000 

IV.  Cannel  *  ... 

45  to  60 

5  to    8 

less  than  1  .  8 

15,700  to  16,200 

15,500  to  16,050 

V.  Bituminous,  high 

grade  

30  to  45 

5  to  14 

1      to    4 

14,800  to  15,600 

14,350  to  14,400 

VI.   Bituminous,  me- 

dium grade.  .  . 

32  to  50 

6  to  14 

2.5to    6.5 

13,800  to  15,100 

11,  300  to  14,400 

VII.   Bituminous,  low 

grade  

32  to  50 

7  to  14 

5      to  12 

12,400  to  14,600 

11,  300  to  13,400 

VIII.  Sub-bituminous 

and  lignite.  .  . 

27  to  60 

10  to  33 

7  .    to  26 

9,600  to  13,250 

7,400  to  11,650 

*  Eastern  Cannel.     The  Utah  cannel  is  much  lower  in  heating  value. 

Air-drying  of  Coal. — In  the  earlier  tests  of  the  Geological  Survey 
the  samples  were  crushed  fine,  spread  out  on  hollow  trays,  and  dried 
in  the  air  of  the  laboratory  for  24  to  96  hours,  or  until  the  loss  be- 
tween successive  weighings  (made  12  to  24  hours  apart)  was  small, 
usually  less  than  1%.  In  the  later  practice  the  coals  after  pulveri- 
zation were  dried  in  a  special  oven  in  a  gentle  current  of  air  of  10° 
to  20°  F.  above  the  temperature  of  the  laboratory.  (Bulletin  U.  S. 
G.  S.  290,  1906,  and  Professional  Paper,  U.  S.  G.  S.,  48,  1907.) 
For  comparison  of  results  see  Bulletin,  U.  S.  G.  S.,  323,  p.  8. 

Different  Methods  of  Reporting  Coal  Analyses. — Much  confusion 
and  trouble  is  experienced  by  students  of  coal  problems  on  account 
of  the  many  different  forms  in  which  chemists  report  the  results  of 
forms  be  adopted  when  results  are  published,  so  as  to  lessen  the 
their  analyses.  It  is  greatly  to  be  desired  that  one  or  two  standard 


74 


STEAM-BOILER  ECONOMY. 


trouble  of  comparing  different  coals,  and,  incidentally,  to  save  space 
and  printers'  ink.  The  proximate  analysis  is  given  for  the  coal  in 
one  or  more  of  five  different  conditions,  viz.,  "as  received,"  "air 
dried,"  "dried  at  105°  C,"  "air-dried  free  from  ash,"  and  "com- 
bustible," or  "ash  and  moisture  free."  Formerly  some  chemists  de- 
ducted half  of  the  sulphur  from  the  volatile  matter  and  half  from 
the  mixed  carbon,  calculating  the  results  so  that  the  sum  of  moisture, 
ash,  volatile  matter  and  fixed  carbon,  modified  as  stated  together  with 
the  sulphur  would  equal  100  per  cent.  This  practice  has  fortunately 
been  abandoned,  and  it  is  now  the  custom  to  report  the  actual  results 
of  the  proximate  analysis  footing  up  100  per  cent  and  to  give  sulphur 
as  separately  determined. 

The  ultimate  analysis  may  also  be  reported  for  the  coal  in  any 
one  or  more  of  the  five  different  conditions  above  named,  but  in 
addition  it  is  the  custom  of  some  chemists  to  report  the  analysis  of 
the  coal  "as  received,"  "air-dried,"  or  "air-dried  ash-free"  in  such  a 
manner  as  to  make  the  hydrogen  and  oxygen  include  the  moisture, 
while  others  report  the  moisture  as  a  separate  item,  thus  making 
eight  different  possible  forms  for  the  record  of  the  ultimate  analysis. 
The  following  table  shows  the  several  ways  in  which  the  analysis  of 
one  sample  of  coal  may  be  reported: 

PROXIMATE   ANALYSIS. 


As 
Received- 

Air-dried. 

Dry  Coal. 

Air-dry, 
Ash-tree. 

Ash-  and 
Moisture-free. 

Moisture  
Volatile 

5 

28 
58 
9 

1           1.04 
28        29.17 
58        60.42 
9          9.37 

28         '29  .'47 

58        61.06 
9          9.47 

1           1.15 
28        32.18 
58         66.67 

28         32.56 
58        67.44 

Fixed  carbon  
Ash 

Loss  on  air-drying 
Sulphur  
B.T.U.  perlb  
Form  No  

100 
4 

1 
13,330 

(1) 

96       100.00 

1.04 
13,886 

(2) 

95       100.00 

1.05 
14,032 

(3) 

87       100.00 

1.15 
15,322 

(4) 

86       100.00 

1.16 
15,500 

(5) 

ULTIMATE    ANALYSIS. 


As 
Received. 

Air-dry. 

Dry  Coal. 

Air-dried, 
Ash-free. 

Ash-and 
Moisture- 
free. 

Moisture  . 
Ash 

5     . 
9         9 
1         1 
5         5.56 
73       73 
1         1 
6       10.44 

1         1  .  04 
9         9.38         9.38 
1          1  .  04         1  .  04 
5         5.21         5.33 
73       76.04       76.04 
1          1.04          1.04 
6         6.25         7.17 

'9      "9A8 
1          1.05 
5         5.26 
73       76  .  84 
1          1.05 
6         6.32 

1         1.15     

1         1.15         1.15 
5         5.75         5.88 
73       83.90       83.90 
1          1.15         1.15 
6         6.90         7.92 

1          1.16 

5         5.81 
73       84.89 
1          1.16 
6         6.98 

s  

H  
C  

N  
O  

Form  No. 

100     100.00 
(6)         (7) 

96     100.00     100.00 
(8)             (9) 

95     100.00 
(10) 

87     100.00     100.00 
(11)           (12) 

86     100.00 
(13) 

COAL. 


75 


The  figures  in  the  columns  footing  respectively  96,  95,  87  and  86, 
are  here  given  to  show  the  figures  that  were  used  in  obtaining  the 
several  percentages;  they  would  be  omitted  in  a  report. 

Here  are  thirteen  different  forms  for  reporting  the  analysis  of  a 
single  sample  of  coal.  Which  of  them  are  useful?  Form  (1)  is  the 
usual  proximate  analysis  as  actually  made;  form  (5)  is  calculated 
directly  from  (1).  If  the  volatile  matter  in  the  combustible  (form  5) 
is  less  than  38  per  cent,  the  heating  value  per  pound  of  combustible 
may  be  approximated  (except  in  the  case  of  some  coals  of  the  far 
West)  with  an  error  of  not  over  2  per  cent  by  means  of  the  figures 
in  the  table  on  page  56,  viz. : 


Vol.  Matter. 

B.T.U.  per  Ib. 

Vol.  Matter. 

B.T.U.  per  Ib. 

Vol.  Matter. 

B.T.U.  per  Ib. 

3 

6 
10 

14,940 
15,210 
15,480 

13 
20 

28 

15,660 
15,840 
15,660 

32 
37 
40 

15,480 
15,120 
14,760 

Beyond  40  per  cent  volatile  matter  the  heating  value  has  no 
direct  relation  to  the  volatile  matter  on  account  of  the  great  varia- 
tion in  the  percentage  of  oxygen  in  that  volatile  matter.  Form  (5) 
is,  therefore,  useful  as  an  indication  of  the  kind  of  coal  and,  with  the 
exceptions  above  mentioned,  of  its  approximate  heating  value.  Form 
(4)  is  important,  since  the  percentage  of  moisture  in  the  air-dried 
coal  is  an  index  to  the  quality  of  the  real  coal  substance,  that  is  the 
coal  free  of  ash  and  of  surface  moisture.  Forms  (2)  and  (3)  are 
of  no  use  for  comparing  classes  of  coal,  until  their  figures  are  con- 
verted into  other  forms,  since  they  include  the  ash,  an  accidental 
variable. 

Of  the  ultimate  analyses,  form  (9)  shows  the  actual  analysis  of  the 
air-dried  coal,  and  it  may  be  useful  as  a  record  of  the  original  results 
obtained,  but  the  figures  are  otherwise  of  no  essential  importance 
until  the  moisture  has  been  separated  from  the  hydrogen  and  oxygen, 
as  in  form  (8),  and  from  ash,  as  in  form  (13).  This  form  (13)  is 
the  one  which  gives  all  the  essential  figures  of  the  ultimate  analysis, 
and  which  shows  the  composition  of  the  combustible. 

Omitting  all  the  unessential  figures  we  may  construct  a  new  table, 
which  gives  all  the  data  that  are  really  needed  for  either  commercial 
or  scientific  purposes,  as  follows: 


76 


STEAM-BOILER  ECONOMY. 

PROXIMATE    ANALYSIS. 


Coal  as  Received. 

Air-dry,  free  from  Ash. 

Combustible. 

Loss  on 
Air-drying. 

Moisture. 

Ash. 

B.T.U. 
per  Ib.   • 

Moisture. 

B.T.U. 

Vol.  Mat. 

B.T.U. 

4.00 

5.00 

9.00 

13,330 

1.04 

15,322 

32.56 

15,500 

ULTIMATE    ANALYSIS. 


B.T.U.  actual 
greater,  + 
or  less  — 
than  Calculated 

s. 

H. 

C. 

N. 

o. 

B.T.U. 

Calculated.* 

1.16 

5.81 

84.89 

1.16 

6.98 

15,427 

-73  =  047% 

*  By  Dulong's  formula. 

If  the  fixed  carbon  is  desired  for  any  purpose  it  may  be  obtained 
by  subtracting  the  volatile  matter,  32.56  from  100,  giving  67.44. 
If  it  is  desired  to  reproduce  the  original  proximate  analysis,  footing 
up  to  100  per  cent,  it  may  be  done  by  multiplying  32.56  and  67.44 
respectively  by  100—  (5.00  +  9.00)  giving  28.0  and  58.0,  but  these 
figures  are  of  no  value  except  as  original  records  of  the  analysis. 

For  the  purpose  of  tabulating  a  long  list  of  coals,  all  the  figures 
above  given  for  both  proximate  and  ultimate  analysis  may  easily  be 
printed  in  a  single  line,  in  6-point  type,  running  lengthwise  of  the 
page.  Bulletin  No.  22  of  the  Bureau  of  Mines  contains  no  less  than 
289  pages  of  analyses,  averaging  about  40  to  the  page,  taking  three 
lines  for  each  coal,  viz.:  "as  received,"  "dried  at  105°,"  and  "moisture 
and  ash-free/'  and  in  some  cases  a  fourth  line  is  given,  "moisture, 
ash  and  sulphur  free."  Both  proximate  and  ultimate  analyses  are 
given  for  each  of  the  three  conditions,  and  yet  the  tables  do  not  give 
several  items  of  important  information  that  are  given  in  the  brief 
table  above,  viz. :  moisture  and  B.T.U.  of  the  air-dried  coal  free 
from  ash ;  B.T.U.  per  Ib.  combustible  calculated  by  Dulong's  formula ; 
and  the  difference  between  that  value  and  the  B.T.U.  per  Ib.  com- 
bustible obtained  by  the  calorimeter.  The  vast  labor  of  calculating 
the  ultimate  analyses  for  coal  as  received  and  as  dried  at  105°  C.,  could 
have  been  saved,  two-thirds  of  the  size  of  the  book  could  have  been 
dispensed  with,  and  the  table  would  have  given  more  information 
to  users  of  the  Bulletin,  if  the  tables  had  been  arranged  in  the  brief 
form  shown  above. 


COAL. 


77 


Reliability  of  Dulong's  Formula.—  Suppose  we  have  a  fuel  whose 
composition  is 

C5H602 

60  +  6  +  32  =  98  parts  by  weight. 

If  the  0  was  inert  or  uncombined,  the  heating  value  of  this  fuel 
would  be 

60  X  146  +  6  X  620  =  12,480  B.T.U.  for  0.98  Ib. 

According  to  the  supposition  of  Dulong's  formula  that  all  of  the 
0  is  combined  with  H,  the  composition  would  be  represented  by 

C5H2  +  2H20 


98.    Heating  value,  60  X  146  +  2  X  620  =  10,000  B.  T.  IT. 

It  is  possible,  however,  that  the  0  and  the  H  may  be  combined  with 
C  in  several  different  ways;  for  example: 

C3H6  +  2CO 
36+6  +  56        =98. 


Heating  Value. 
36X146  +  6X620+56X44.5  =  11,468  B.T.U. 


or 
C4H6C02 

48  +  6  +  44 

or 


98.       48X146  +  6X620 


=10,728 


48+4+28  +  18  =  98.      48X146+4X620+28X44.5=10,736         " 


or 


54  +  8  +  36        =98.       54X146  +  8X236 
or 


=   9,772 


36  +  16  +  28  +  18          36X146  +  16X236+28X44.5  =  10,278        " 

Showing  that  the  heating  value  may  range  from  14.7%  greater  to 
2.3%  less  than  that  calculated  by  Dulong's  formula. 

The  table  of  Mahler's  results,  page  143,  shows  that  the  actual  heat- 
ing value  of  a  cannel  coal,  No.  26,  was  3.28%  less  than  that  cal- 
culated by  Dulong's  formula;  that  of  a  lignite,  No.  33,  was  4.75% 
greater;  turf  from  Bohemia,  14.2%  greater;  two  samples  of  wood 
averaged  9.1%  greater;  and  cellulose  16.1%  greater  than  the  cal- 
culated value. 

Let  us  apply  some  of  the  above  suppositions  to  two  of  these 
cases,  the  cannel  coal  and  the  cellulose. 


78  STEAM-BOILER  ECONOMY. 

The  actual  heating  value  of  the  combustible  of  the  cannel  coal 
is  8431  calories;  calculated  value  8717;  difference  286,  or  3.28% 
of  the  calculated  value.  Its  composition  is  C,  83.79;  H,  6.57;  0  +  N, 
9.64.  Taking  tf  =  1,  assuming  that  1.08  H  is  combined  with  8.64  0 
as  H20  and  that  the  remaining  5.49  H  is  combined  with  16.47  C 
as  CH4  we  have 

83.79  -  16.47  =  67.32  C      X     81.40  =  5480  calories 
5.49  +  16.47    =  21.96  CH4  X  131.20  =  2881       " 

Total  8361  calories,  which  is  only  70  calories  or  0.83%  less  than 
the  actual  value. 

The  cellulose,  C12H10010  is  44.44  C;  6.17  H;  49.39  0;  actual  heat- 
ing value  4200  calories;  calculated  by  Dulong's  formula  3617.     Dif- 
ference 58.3  calories,  or  14%  of  the  actual  value. 
Suppose  that  the 

49.39  0  is  combined  with  3/11  of  49.39  or  13.47  C  as  C02 

and         6.17  H"         "  "     3X6.17          or  18.51  C  as  CH4, 

leaving  12.46  C  uncombined;  we  then  have 

6.1"<  +  18.51  C  =  24.68  CH4  X  131.20  =  3238 
12.46  C       X    81.40  =  1014 
Total  4252  calories,  as  compared  with  4200,  the  actual  value. 

Dulong's  formula,  however,  gives  results  that  are  remarkably 
close  to  the  actual  with  all  ordinary  coals.  It  is  only  with  lignite, 
wood  and  other  fuels  high  in  oxygen,  and  in  some  fuels  high  in 
hydrogen,  such  as  cannel  coal  and  methane,  CH4,  that  it  fails.  The 
actual  heating  value  of  CH4,  according  to  Thomsen  is  13,120  calories, 
while  its  value  calculated  by  Dulong's  formula  is  14,730  calories, 
the  difference,  1610  calories,  being  12.27%  of  the  actual  value. 

Nature  of  the  Volatile  Matter  in  Coal.— H.  C.  Porter  and  F.  K. 
Ovitz,  of  the  U.  S.  Geological  Survey,  in  a  paper  presented  to  the 
American  Chemical  Society  in  1909,*  gave  the  following  tables  of 
results  obtained  by  heating  samples  of  coal  to  different  temperatures. 
They  show  that  the  volatile  product  of  coal  is  to  some  extent  incom- 
bustible, that  the  proportion  of  inert  volatile  varies  in  different  coals, 
and  that  the  oxygen  of  coal  is  in  many  cases  evolved  in  the  volatile 
matter  very  largely  in  combination  with  carbon  as  CO  and  C02  as 
well  as  with  hydrogen  as  water,  thereby  explaining  in  great  degree 
the  discrepancy  found  in  these  cases  between  the  determined  calorific 
value  and  that  calculated  by  Dulong's  formula. 

*  See  also  Bulletin  No.  1  of  the  U.  S.  Bureau  of  Mines. 


COAL. 


79 


TABLE  I. 

ANALYSIS   OF   COAL   USED   IN   EXPERIMENTS. 


Moisture. 

V.  M. 

F.  C. 

Ash. 

Connellsville,  Pa  
Ziegler  111 

1.10 

7  67 

30.67 
30  38 

60.35 

e;4   QO 

7.88 
7  fi^ 

Sheridan  Wyo 

9  15 

39  93 

42  92 

Q  no 

Pocahontas,  W.  Va 

0  35 

20  93 

75  51 

Q    01 

TABLE  II. 

AVERAGE    RESULTS   OF    10    GRAMS   AIR-DRIED    COAL. 


Coal. 

High- 
est 
Tern, 
in 
Coal. 

Tar. 

Water. 

Gas. 

(CCS) 

Gas  Composition. 
(Calculated  to  undiluted  gas.) 

C02. 

£ 

j3 

CO. 

CH4 

4 

H.I 

N. 

10  minutes  heating  at  500°  C. 
Connellsville.  Pa  
Ziegler,  111  

10  minutes  heating  at  600°  C. 
Connellsville,  Pa  
Ziegler  111 

335 
325 

441 
440 

562 
545 
580 
599 

.687 
680 

4.9 
6.8 

11.0 

7.8 
8.2 
4.2 

12.6 
9.3 

7.9 
6.5 

3.2 
13.0 

3.5 
14.0 
18.5 
1.9 

4.5 
13.9 
19.1 
2.4 

8 
90 

190 
173 

583 
471 
1020 
675 

1375 
1251 
1780 
1590 

30.0 
14.8 

6.3 
15.7 

3.0 

8.5 
28.8 
1.9 

s'.s 

19.8 
1.2 

0 
0 

8.2 
7.0 

7.2 
5.1 
3.7 

4.4 

5.5 
3.8 
2.7 
3.4 

6.5 
5.3 

5.9 

14.4 

5.4 
13.7 
20.0 
3.9 

6.9 
16.0 
21.4 
4.8 

6.5 
8.0 

36.9 
19.0 

44.1 
59.6 
18.6 
44.4 

24.9 

27.7 
14.1 
24.4 

7.0 

23.7 
22.2 

17.7 
0 
6.8 
16.1 

12.1 
6.1 
4.0 
11.6 

0 
0 

2.0 

2.8 

13.3 
1.1 
15.1 

28.5 

33.1 
33.7 
30.0 
43.2 

50.0  (6) 
71.9(6) 

17.0  (6) 
18.9  (6) 

9.1 
12.0 
7.0 
0.8 

16.0  (6) 

1:8  <w 

11.4 

10  minutes  at  700°  C. 
Connellsville,  Pa  
Ziegler,  111 

Sheridan,  Wyo  
Pocahontas,  W.  Va  

10  minutes  at  800°  C. 

Ziegler,  111  
Sheridan,  Wyo  
Pocahontas,  W.  Va.  ...... 

(a)   Includes  all  higher  paraffin  hydrocarbons  calculated  as 
(6)    Includes  small  amount  of  air. 

TABLE  III. 

ABSOLUTE    QUANTITIES   OF   SMOKING   AND   NON-SMOKING   PRODUCTS. 

(10  Minutes  Heating  of  10  grams  Air-dried  Coal.) 


Tempera- 
ture °C. 

Smoking  Products. 

Nonsmoking  Gases  (cu.cm,). 

Designation  of 

Gas  (cu.cm.). 

Coal. 

Furn- 
ace. 

Coal. 

Tar, 
Per 

CO2. 

CO. 

CH4. 

H. 

Total' 

Cent. 

Ilium. 

Ethane, 

Total. 

etc. 

Connellsville,  Pa.  . 
Ziegler,  111  

500 
500 

335 
325 

0 
0 

0.6 
0 

0.6 
0 

2.4 
13.5 

0.5 

4.7 

0.5 
7.2 

0 
0 

3.4 
25.4 

Connellsville,  Pa.  . 
Ziegler,  111. 

600 
600 

441 
440 

4.9 
6.8 

16 
12 

46 
39 

61 
51 

12 

26 

11 
25 

71 
33 

4 
5 

98 
91 

Connellsville,  Pa.  . 
Ziegler,  111  
Sheridan,  Wyo.  .  .  . 
Pocahontas,  W.  Va. 

700 
700 
700 
700 

562 
545 
580 
599 

11.0 
7.8 
8.2 
4.2 

42 
24 
38 
30 

103 
0 
69 
109 

145 
24 
107 
138 

18 
40 
294 
13 

31 
64 

204 
27 

256 

281 
190 
300 

78 
5 
154 
192 

383 
391 

842 
532 

Connellsville,  Pa.  . 
Ziegler,  111  
Sheridan,  Wyo  
Pocahontas,  W.  Va. 

800 
800 
800 
800 

687 
680 

12.6 
9.3 
7.9 
6.5 

76 
47 
48 
54 

166 
76 

72 
186 

242 
123 
120 
240 

21 
47 
355 
19 

95 
200 
381 

77 

343 
346 
,254 
390 

458 
420 
534 
691 

917 
1013 
1524 
1177 

80  STEAM-BOILER  ECONOMY. 

Relation  of  Quality  of  Coal  to  the  Capacity  and  Economy  of  a 
Boiler. — The  actual  evaporating  capacity  of  a  boiler  containing  a 
given  amount  of  heating  surface  and  a  given  area  of  grate  depends 
primarily  upon  the  quantity  of  heat  which  may  be  generated  in  the 
furnace.  This  depends  on  the  quantity  of  coal  that  may  be  burned, 
and  also  on  its  quality.  The  better  the  quality  the  greater  number 
of  heat-units  will  be  generated  by  the  combustion  of  each  pound.  If 
the  coal  is  high  in  moisture  or  in  oxygen,  not  only  will  the  heat-units 
derived  from  a  pound  of  it  be  low,  but  the  attainable  temperature  will 
also  be  lower  than  that  attainable  from  a  better  coal;  and  furnace 
temperature,  as  will  be  shown  in  another  chapter,  is  an  important 
factor  of  both  capacity  and  economy. 

If  the  coal  is  high  in  ash,  not  only  is  its  value  per  ton  diminished, 
but  the  quantity  of  ash  formed  on  the  grate  tends  to  check  the  air- 
supply,  and  therefore  to  diminish  the  rate  of  combustion,  and  conse- 
quently the  quantity  of  steam  generated.  If  the  coal  is  high  in 
sulphur,  the  ash  will  be  apt  to  fuse  into  clinker,  and  this  may  choke 
the  grates  completely,  necessitating  frequent  cleaning  of  the  fire,  in- 
volving extra  labor,  loss  of  unburned  coal  removed  with  the  ashes  in 
cleaning,  the  loss  of  heat  of  the  furnace  by  keeping  the  fire  doors  open 
during  the  time  of  cleaning. 

In  order  to  develop  the  rated  capacity  of  a  boiler  with  poor  coal 
high  in  ash,  it  is  necessary  to  have  either  a  larger  grate  surface  or 
stronger  draft  than  with  good  coal.  Sometimes  strong  draft  is  of  no 
avail,  on  account  of  the  clinkering  of  the  ash,  and  in  such  a  case  large 
grate  surface  is  absolutely  required. 

The  quality  of  coal,  therefore,  is  a  most  important  factor  of  both 
the  capacity  and  economy  of  a  boiler.  It  is  possible  with  a  good  free- 
burning  coal  to  obtain  from  a  given  boiler  twice  as  much  steam  as 
can  be  obtained  with  the  same  boiler  and  the  same  draft  from  poor 
coal,  and  the  relative  economy  obtainable  with  the  two  coals,  or  the 
steam  generated  per  pound  of  coal,  may  differ  30  or  40  per  cent. 

The  quality  of  the  coals  of  the  United  States  varies  greatly  in  dif- 
ferent districts.  In  some  limited  districts  the  very  best  quality  is 
regularly  found;  in  other  districts  the  quality  is  uniformly  from  good 
to  medium,  and  in  still  others  it  ranges  from  poor  to  worthless. 

To  buy  coal  on  the  reputation  of  the  district  in  which  it  is  mined 
is  not  as  good  a  way  as  to  buy  it  on  a  guarantee  of  quality,  as  deter- 
mined by  an  analysis  for  water,  volatile  matter,  ash,  and  sulphur,  but 
it  is  the  most  common  way.  A  knowledge  of  the  quality  of  coals 


COAL. 


81 


found  in  different  districts  is  therefore  of  some  importance.  Another 
chapter,  "Coal-fields  of  the  United  States,"  is  devoted  to  this  subject. 
It  is  usually  found  that  under  the  most  favorable  conditions  of 
firing,  moderate  rate  of  driving  and  proper  air  supply,  the  maximum 
boiler  efficiency  is  obtained  only  with  coal  of  a  high  heating  value  per 
pound  of  combustible.  This  is  accounted  for  by  the  fact  that  the  coals 
that  have  a  low  heating  value  per  pound  of  combustible  are  usually  high 
in  volatile  matter  and  in  moisture.  It  is  difficult  to  burn  all  the 
volatile  matter  when  its  quantity  is  excessive,  and  the  excessive  mois- 
ture not  only  carries  away  heat  in  the  chimney  gases  but  it  also  tends 
to  lower  the  temperature  of  the  fire  and  thus  to  reduce  efficiency. 


/ 

t  .  . 

'! 

/, 

•' 

• 

/ 

a 

© 

1 

'J  c 

1 

17  Coals  above 
7250  B.-T-JUv-pfer- 
3.  coJnbusltible 
.ll-above-62-^  

•ffic'H 

ji 

8  Co 
All 

ils.be 

jelow 

Ell 

4,260 
fe*, 

B.T. 

'  ( 

•  I 

TTI 

62  f, 

?ll      1      1 

12000        13000       14000       15000        1600C 
B.T.U.  per  Ib.  Combustible 


FIG.  4. — RELATION  OF  HEATING  VALUE  AND  EFFICIENCY. 
The  tendency  of  efficiency  to  vary  with  the  heating  value  per  pound 
of  combustible  is  well  shown  by  the  results  of  the  tests  of  the  U.  S. 
Geological  Survey  made  at  St.  Louis  in  1904,*  which  are  given  in  the 
table  on  page  82. 

The  relation  of  the  boiler  efficiency  to  the  heating  value  per  pound 
of  combustible  is  plotted  in  the  accompanying  chart. 

In-  14  out  of  the  23  States  coals  were  obtained  having  heating 
values  between  14,290  and  15,700  B.T.U.  per  pound  combustible,  and 
which  gave  boiler  efficiencies  of  from  64  to  67.6  per  cent.  For  15 
out  of  17  coals  from  these  States,  the  results  are  plotted  in  the  narrow 
field  at  the  top  of  the  diagram,  and  they  may  all  be  represented  by 
the  equation  E  =  69  -  2.5  (16  -  H)  ±  1,  in  which  H  is  the  heating 
value  per  pound  combustible  in  thousands  of  B.T.U.  The  coals  of 
lower  heating  value  than  14,290  all  gave  efficiencies  below  62  per  cent, 
ranging  down  to  53.11  per  cent  for  the  Ehode  Island  graphitic  coal. 

*  Bulletin  No.  23  of  the  U.  S.  Bureau  of  Mines,  1912. 


82 


STEAM-BOILER  ECONOMY. 


TABLE  SHOWING  NUMBER  OF  COALS  TESTED  FROM  EACH  STATE  AND  AVERAGES  OF 

PRINCIPAL   RESULTS. 


State. 

Kind  of  Coal. 

No.  of 
Coals. 

Per- 
centage 
of 
Build- 
ers 
Rated 
Horse- 
power. 

Equiva- 
alent 
Evapo- 
ration 
Coal  as 
Fired  at 
and 
from 
212°  F. 

Effi- 
ciency 
of 
Boiler 
and 
Grate. 

Effi- 
ciency 
of 
Boiler. 

B.T.U. 
per  Ib. 
of  Dry 
Coal. 

B.T.U. 
per  Ib. 
of 
Com- 
bustible 

Alabama 

Bituminous 

4 

91.9 

8.08 

64.31 

66  42 

12,656 

15  016 

Arkansas  

Semi-bit  
Lignite* 

7 
1 

89.3 
104  0 

8.77 
3.59 

63.54 
59.26 

66.81 
60.25 

13,707 
9,549 

15,473 
12  180 

Colorado  
Florida  

Bituminous.  . 
Peatf  

1 
1 

71.9 
113.2 

5.78 
5.00 

55.36 

57.85 

61.26 
58.19 

12,577 
10,082 

13,478 
11,003 

Illinois 

Bituminous 

25 

89.6 

7.05 

62.66 

64.60 

12,249 

14,294 

5 

90  7 

6  24 

59  55 

61  83 

11,650 

14  216 

Indiana 

11 

89  5 

7  33 

63.76 

65.28 

12,549 

14,504 

Indian  Territory.  . 
Kansas 

4 
6 

94.9 
83  4 

7.73 

7  72 

61.69 
61.26 

64.04 
63.17 

12,820 
12,780 

14,561 
14  949 

Kentucky  (East)  . 
(West) 
Maryland  

Semi-bit  . 

3 
3 
1 

91.0 

88.9 
80.1 

9.33 
7.70 
8  90 

65.41 
62.82 
63  96 

66.69 
64.73 
65  29 

14,417 
12,883 
13,680 

15,169 
14,547 
15,681 

Missouri 

Bituminous 

7 

92  2 

6  73 

60  18 

62  99 

12  246 

14  465 

New  Mexico.  . 

North  Dakota. 
Ohio 

Lignitic  
Bituminous.  . 
Lignite  
Bituminous 

2 
3 
1 
9 

96.5 
104.2 
71.3 
92  2 

6.15 
8.11 
3.79 
8  32 

55  .  45 
64.68 
53.29 
64  88 

58.96 
66.50 
55.34 
66  31 

12,021 
12,507 
10,719 
13  130 

14,009 
14,941 
12,511 
14  740 

Pennsylvania  . 

Semi-bit  

9 

89.9 

9.48 

66.22 

67  .  53 

14,218 

15,595 

Rhode  Island. 
Tennessee 

Graphitic  
Bituminous 

1 
9 

55.8 
102  3 

4.81 
8  43 

40.91 
64   18 

53.11 
65  55 

11,639 
13  264 

14,001 
15  093 

Texas  

Lignite  .  .  . 

1 

86  1 

4   19 

53  34 

55  48 

11  102 

12  731 

Virginia 

4 

94  2 

9  36 

65  07 

66  28 

14  436 

15  281 

Washington  
West  Virginia.  .  .  . 

Lignitic  
Semi-bit  

2 
21 

98.7 
95.5 

7.85 
9  54 

63^45 
65  89 

65.25 
67  64 

12,725 
14,451 

14,599 
15,544 

Wyoming  

Lignite    . 

5 

87  7 

5  75 

56  85 

59  85 

11  337 

13  572 

*  Forced  draft. 


t  Natural  draft,  0.8  inch  of  water. 


Effect  of  Size  of  Coal  on  Boiler  Efficiency.  (A.  Bement,  Jour. 
Western  Soc'y  of  Engrs.,  Dec.  1906). — The  size  of  the  pieces  of  coal 
exercise  an  important  influence,  not  only  on  the  capacity  which  may 
be  produced  by  a  boiler,  but  on  the  resulting  efficiency,  and  the  best 
size  to  be  used  in  a  given  case  is  dependent  upon  many  conditions, 
such  as  the  strength  of  draft,  kind  of  stoker  or  grates,  method  of 
firing,  etc.,  and  the  selection  of  the  proper  size  of  fuel  or  the  niethod 
of  utilizing,  the  available  size,  often  affords  an  opportunity  to  effect 
important  economies. 

Valuing  Coals  by  Test  and  by  Analysis.— The  best  way  to  obtain 
the  relative  value  of  different  coals  for  any  particular  steam-boiler 
plant  is  to  have  a  car-load  of  each  coal  tested  under  the  ordinary  run- 
ning conditions  of  the  plant,  and  then  to  check  the  results  by  a  proxi- 
mate analysis  of  each.  The  coal  that  is  most  economical  for  one 
boiler-plant  is  not  necessarily  the  most  economical  for  another,  on 
account  of  the  differences  in  conditions,  such  as  kind  of  furnace,  area 


COAL.  83 

of  grate  surface,  draft  available,  etc.*  A  plant  designed  for  the  pur- 
pose may  be  able  to  use  with  satisfaction  the  poorest  quality  of  the  fine 
sizes  of  anthracite,  while  another  may  not  be  able  to  use  anything 
cheaper  than  the  best  pea  coal,  and  still  another,  having  deficient  grate 
surface,  may  be  compelled  to  use  egg  size,  or  even  semi-bituminous. 

Besides  testing  the  coals  by  burning  them  under  the  boilers  and 
weighing  the  quantity  of  water  evaporated,  a  proximate  analysis  of 
each  coal  should  be  made  so  as  to  arrive  at  a  standard  of  quality 
by  reference  to  which  future  purchases  may  be  made. 

Selection  of  Coal  for  Steam-boilers, — The  selection  of  the  kind  of 
coal  to  be  used  in  any  given  boiler-plant  depends :  ( 1 )  on  the  relative 
cost  per  ton  of  the  different  kinds  delivered  at  the  boiler;  (2)  on  their 
relative  total  heating  value  per  pound  or  per  ton;  (3)  on  the  relative 
percentage  of  the  heating  value  which  may  be  utilized  in  the  boiler; 
(4)  on  the  maximum  capacity,  or  horsepower,  which  may  be  developed 
by  the  boilers  with  different  coals;  (5)  on  the  relative  cost  of  handling 
the  different  coals  and  the  ashes  produced  from  them;  and  (6)  on 
their  relative  smokelessness  when  used  in  the  particular  boilers  and 
furnaces  under  consideration. 

In  some  locations  only  one  kind  of  coal  is  practically  available,  as 
when  the  boilers  are  located  near  a  coal-mine,  all  other  kinds  being 
relatively  too  high-priced  on  account  of  the  freight  that  must  be  paid 
on  them.  In  such  cases,  for  the  best  results,  the  furnace  and  the 
draft  must  be  adapted  to  the  coal  at  hand.  If  the  coal  is  of  poor 
quality,  the  grate  surface  must  be  large  relatively  to  the  heating  sur- 
face. If  it  is  anthracite  rice  or  culm,  the  draft  must  be  strong,  and, 
unless  the  grate  surface  is  very  large,  mechanical  draft  may  be  nec- 
essary. If  the  coal  is  bituminous,  the  area  of  the  grate,  in  proportion 
to  the  heating  surface,  will  depend  on  the  quality;  the  poorer  the 
quality  the  larger  the  grate  required.  In  other  locations  many  different 
varieties  of  coal  may  be  available,  and  then  all  of  the  points  above 
enumerated  may  have  to  be  taken  into  account  in  making  a  selection. 

Usually  the  coal  which  is  sold  at  the  lowest  price  per  ton  is  the 
most  economical  one  for  those  furnaces  and  boilers  that  are  adapted  to 
it.  Its  price  is  apt  to  be  depreciated  below  the  normal  price  due  to  its 

*  An  example  of  this  is  seen  in  locomotive  practice,  in  which  it  is  found 
that  semi-bituminous  coal  of  the  highest  heating  value  does  not  give  as  high 
economy  at  high  rates  of  driving  as  eastern  bituminous  coal,  which  is  about 
5%  lower  in  heating  value,  on  account  of  the  fact  that  a  larger  percentage  of 
semi-bituminous  coal  is  blown  out  of  the  stack  in  the  shape  of  sparks  and  cinders. 


84  STEAM-BOILER  ECONOMY. 

heating  value,  because  its  market  is  limited  by  the  number  of  boilers 
lo  which  it  is  adapted,  and  also  by  the  cost  of  freighting  it  to  more 
distant  markets.  Freight  charges  being  the  same  per  ton  on  poor 
as  on  good  coal,  it  does  not  pay  to  haul  poor  coal  long  distances ;  it  is 
better  to  sell  it  at  a  relatively  low  price  in  nearby  markets.  On  the 
other  hand,  good  coals  are  apt  to  be  relatively  overvalued  in  the  mar- 
ket, since  they  can  be  used  in  all  kinds  of  furnaces,  are  more  desirable 
in.  every  way,  and  they  may  be  transported  long  distances  to  find  the 
best  markets.  On  this  account  a  boiler  and  furnace  should  be  adapted, 
whenever  possible,  to  use  the  poorest  kind  of  coal  in  the  market. 

But  this  is  not  always  possible.     The  boiler  and  chimney  being' 
already  in  place  and  the  requirements  of  the  engines  being  such  that 
the  boiler  must  be  driven  to  its  maximum  capacity,  then  a  coal  must 
be  selected  from  which  this  maximum  capacity  may  be  obtained. 

For  maximum  evaporation  per  pound  of  coal,  that  coal  should  be 
selected  in  which  the  product  of  its  total  heating  value  per  pound  by 
the  percentage  of  this  heating  value  which  may  be  utilized  by  the 
boiler,  is  a  maximum.  For  instance,  suppose  an  anthracite  egg-coal 
of  a  heating  value  of  13,000  heat  units  per  pound  and  a  good  bitumi- 
nous coal  of  14,000  heat  units  are  equally  available,  but  the  furnace  is 
such  that  the  boiler  will  give  75  per  cent  efficiency  with  the  anthracite 
and  only  65  per  cent  with  the  bituminous,  then  the  relative  values  of 
the  two  coals  for  that  particular  boiler  are  975  for  the  anthracite  and 
910  for  the  bituminous.  If  a  semi-bituminous  coal  with  a  heating 
value  of  14,500  heat  units  is  also  available,  and  the  boiler-efficiency 
with  that  coal  is  70  per  cent,  then  its  relative  figure  will  be  1015.  If 
maximum  capacity,  rather  than  economy,  is  the  prime  consideration, 
then  the  bituminous  coal,  with  the  lowest  relative  economy  of  the 
three,  may  be  selected  if  it  is  found  that  it  is  more  free-burning  than 
the  others,  so  that  a  larger  quantity  of  it  may  be  burned  in  the  fur- 
nace with  the  draft  that  is  available.  If  economy  of  cost  is  the  chief 
consideration,  the  boiler  having  ample  capacity  with  either  fuel,  then 
that  coal  will  be  selected  which  evaporates  the  most  water  for  the 
least  money,  or  in  case  of  the  three  coals  considered,  the  one  in  which 
its  price  per  ton  divided  by  its  relative  value  figure,  975,  910,  or 
1015,  as  the  case  may  be,  is  the  least.  If  their  costs  per  ton  are  re- 
spectively $1.95,  $1.82,  and  $2.03,  ,then  the  prices  of  the  coals  are 
directly  proportioned  to  their  available  actual  values  for  the  particular 
case,  and  as  far  as  cost  is  concerned  it  is  a  matter  of  indifference 
which  is  selected.  The  selection  may  then  depend  on  the  trifling 


COAL.  85 

difference  between  the  coals  in  the  relative  cost  of  handling  them,  or 
in  handling  the  ash  made  from  them,  the  bituminous  coal  usually 
requiring  the  greater  labor  on  the  part  of  the  fireman.  If  the  location 
is  in  a  city,  where  smoke  is  objectionable,  the  anthracite  coal  may  be 
selected  on  account  of  its  smokelessness. 

Specifications  for  Purchase  of  Coal. — It  is  customary  with  very 
large  consumers  of  coal  to  issue  specifications  of  quality,  upon  which 
sellers  are  asked  to  make  bids,  and  on  receipt  of  the  coal  to  have  it 
carefully  sampled  and  tested  to  ascertain  whether  it  is  of  the  quality 
prescribed.  The  following  specifications  are  recommended  by  the 
author : 

Anthracite  and  Semi-anthracite. — The  standard  is  a  coal  con- 
taining 5  per  cent  volatile  matter,  not  over  2  per  cent  moisture,  and 
not  over  10  per  cent  ash.  A  premium  of  0.5  per  cent  on  the  price  will 
be  given  for  each  per  cent  of  volatile  matter  above  5  per  cent  up  to 
and  including  15  per  cent,  and  a  reduction  of  2  per  cent  on  the  price 
will  be  made  for  each  1  per  cent  of  moisture  and  ash  above  the 
standard. 

Semi-bituminous  and  Bituminous. — The  standard  is  a  semi-bitu- 
minous coal  containing  not  over  20  per  cent  volatile  matter,  2  per 
cent  moisture,  6  per  cent  ash.  A  reduction  of  1  per  cent  in  the  price 
will  be  made  for  each  1  per  cent  of  volatile  matter  in  excess  of  25  per 
cent,  and  of  2  per  cent  for  each  1  per  cent  of  ash  and  moisture  in 
excess  of  the  standard. 

Western  Coals. — For  Western  coals,  in  which  the  volatile  matter 
differs  greatly  in  its  percentage  of  oxygen,  the  above  specification  may 
not  be  sufficiently  accurate,  and  it  is  well  to  introduce  the  heating 
value,  as  determined  either  by  a  calorimeter  or  by  a  calculation  from 
the  ultimate  analysis,  as  below : 

The  standard  is  a  coal  containing  not  over  6  per  cent  moisture  and 
10  per  cent  ash  in  an  air-dried  sample,  and  whose  heating  value  is 
14,500  B.T.U.  per  pound  of  combustible.  For  lower  heating  value  of 
the  combustible  the  price  shall  be  reduced  proportionately,  and  for 
each  1  per  cent  increase  in  ash  or  moisture  above  the  specified  figures, 
2  per  cent  of  the  price  shall  be  deducted. 

Government  Coal  Purchases  under  Specifications.  (Bureau  of 
Mines  Bulletin  No.  41,  1912). — In  order  to  award  a  contract  properly, 
the  proposals  should  be  reduced  to  a  common  basis  for  comparison. 
The  preferable  method  is  to  adjust  all  bids  on  a  given  lot  of  coal  to 
the  same  ash  percentage  by  selecting  as  the  standard  that  proposal 


86 


STEAM-BOILER  ECONOMY. 


which  offers  the  coal  containing  the  lowest  percentage  of  ash.  Each 
1  per  cent  of  ash  above  that  of  this  standard  is  assumed  to  have  a 
negative  value  of  2  cents  a  ton,  the  amount  of  the  penalty  which  is 
exacted  under  the  contract  requirements  for  1  per  cent  excess  of  ash. 
The  proposal  prices  are  all  adjusted  in  this  manner  and  are  so 
tabulated.  On  the  basis  of  the  adjusted  price,  allowance  is  then  made 
for  the  varying  heat  values  by  computing  the  cost  of  1,000,000 
British  thermal  units  for  each  coal  offered.  In  this  way  the  three 
variables — calorific  value,  percentage  of  ash,  and  basic  price  per  ton — 
are  all  merged  into  a  single  figure,  the  cost  of  1,000,000  British 
thermal  units,  by  which  one  bid  may  be  readily  compared  with 
another. 

An  example  of  this  manner  of  abstracting  bids  is  shown  below : 


Commer- 

Heating 

Price  per  Ton. 

Bidder. 

cial 
Designa- 
tion of 

Mine  and 
Location.* 

Coal 
Bed.* 

Value  of 
Coal  "as 
Re- 

Ash in 
"Dry 
Coal." 

Cost  per 
1,000,000 
B.T.U. 

Plus  Ash 

Coal.* 

ceived." 

Bid. 

Differ- 

ence. 

B.  t.  u. 

Per  cent. 

Cents. 

A 

13,400 

10   0 

$2.35 

$2.43 

8.096 

B 

14,000 

8.0 

3^15 

3^19 

10  '  172 

c 

14,600 

6.0 

3.25 

3.25 

9  938 

D 

13,000 

10.0 

3.10 

3.18 

10.920 

E 

13,000 

8.0 

2.35 

2.39 

8.207 

F 

13,000 

10.5 

2.35 

2.44 

8.379 

G 

11,500 

13.5 

2.25 

2.40 

9.317 

*  These  columns  are  filled  in  from  data  given  in  proposals. 

The  heating  values  stipulated  by  the  different  bidders  being  dif- 
ferent, the  calorific  cost  is  computed  for  each  bid  by  the  formula  : 


1,000.000  X  adjusted  price  per  ton 
X  -t>.  JL.   U. 


Government  contracts  in  1909-11  were  based  either  on  a  standard 
heating  value  for  coal  "as  received"  and  a  standard  percentage  of  ash 
"dry  coal"  or  on  an  ash  "dry  coal"  standard  only.  The  first  basis  is 
applicable  to  all  coals,  the  second  to  anthracite  only.  For  1912-13  the 
heating  value  is  expressed  on  the  "dry  coal"  basis.  Eor  forms  for 
specifications  and  proposals  see  Technical  Paper  15,  Bureau  of  Mines, 
1912. 


COAL. 


87 


Two  classes  of  coal,  anthracite  and  bituminous,  are  recognized  in 
Government  specifications.  By  bituminous  coal  is  meant  varieties 
other  than  anthracite,  including  the  several  grades  of  semi-bituminous 
and  sub-bituminous. 

As  the  coal  is  weighed  when  delivered,  and  payments  are  made 
according  to  the  price  per  ton,  it  is  necessary  to  determine  the  heating 
value  of  the  coal  in  the  condition  in  which  it  is  received  with  what- 
ever moisture  it  may  then  contain.  A  further  correction  in  payment 
is  made  for  variation  in  ash  in  dry  coal  in  order  to  take  account  of  the 
cost  of  handling  additional  fuel  and  ash  and  of  its  effect  on  the 
capacity  of  the  boiler  and  furnace. 

In  purchasing  anthracite  on  the,  single  standard,  corrections  of  the 
contract  price  are  made  as  in  the  following  table ; 


Size. 

Standard  Ash. 

If  Ash  is  Per  Cent  above  (or  below)  Standard 

^ 

l 

1H 

2 

2^ 

3 

Deduct  (or  Add)  Cents  per  Ton. 

Furnace  and  egg.  .  .  . 
Stove  
Chestnut  

8.01-12 
10.01-14 
12.01-16 
14.51-17 

17.  01-19  {£ 

15 

15 
15 
5 
4 
4 

18 
18 
18 
7.5 
8 
6 

21 
21 
21 
10 
14 
8 

24 
24 
24 
12.5 
21 
10 

27 
27 
15 
32 
12 

48 

Pea 

Buckwheat  

a,  cents  per  ton  to  be  deducted  if  ash  is  above  standard. 
6,  "  ' '  added  if  ash  is  below  standard. 

In  purchasing  bituminous  coal  no  deduction  is  made  if  the  ash 
not  more  than  2  per  cent  higher  than  that  named  in  the  proposal. 
For  higher  percentages  deductions  are  made  as  below: 


is 


Ash  above  proposal,  %  2.01-3 
Cents  per  ton  deducted      2 

If  ash  proposed  is 5  to  7 

Maximum  limit  is .  ,  7 


3.01-4  4.01-5     5.01-6    6.01-7 

4  7  12  18 

8  to  10        11  to  14        15  to  18% 
6  5  4%  higher 


Corrections   for   variation   in   heating  value   above   or  below  the 
standard  established  in  the  contract  are  determined  by  the  formula 


Delivered  B.T.U. 
Standard  B.T.U. 


X  contract  price  =  price  to  be  paid. 


STEAM-BOILER  ECONOMY. 


U.  S.  GOVERNMENT  TESTS,  1909-1910. 

ANTHRACITE. 


As  Received. 

Volatile 

B.T.U. 

Per  Cent 
of  Com- 
bustible. 

per  Ib. 
Combus- 
tible. 

Location  and  Size. 

Moisture. 

Ash. 

Sulphur. 

6.06 

13.83 

0.75 

9.0 

14,940 

Anthracite  screenings 

4.17 
5.93 

10.86 
16.80 

0.79 
0.95 

7.0 
8.7 

14,890 
14,700 

Phila.  &  Reading  anthracite  screenings 
Pittston,  No.  2  buckwheat 

5.29 
3.62 

12.96 
17.16 

0.89 
0.82 

6.9 
7.3 

14,890 
14,900 

Anthracite  screenings 
Pittston,  pea 

6.26 

17.20 

0.82 

8.4 

14,850 

No.  2  buckwheat 

3.33 

13.47 

0.64 

7.6 

14,870 

Plymouth,  No.  1  pea 

4.93 

16.90 

0.65 

6.7 

14,810 

Lehigh  pea 

5.45 

14.00 

0.64 

10.5 

14,950 

Nanticoke,  barley 

3.67 

9.62 

0.66 

6.1 

15.000 

egg 

3.34 

10.84 

0.65 

5.5 

14,820 

Kingston,  grate 

2.12 
3.38 

15.65 
9.31 

0.58 
0.60 

10.7 
5.5 

15,290 
14,990 

Bernice,  egg 
Moreau  &  Lehigh,  broken 

4.55 

17.87 

0.59 

5.9 

14,760 

Phila.  &  Reading,  No.  1  buckwheat 

6.21 

17.45 

0.56 

7.4 

14,600 

Girard,  Mammoth,  No.  2  buckwheat 

SEMI-BITUMINOUS. 


1.92 

7.13 

1.39 

21.5 

15,720 

Cambr  a  Co.,  Pa.,  run-of-mine 

2.16 

6.29 

1.86 

22.5 

15,710 

6.06 

13.83 

0.75 

21.5 

15,680 

2.59 

8.21 

2.44 

23.9 

15,610 

1.98 

8.84 

2.23 

24.0 

15,590 

2.19 

6.43 

1.59 

22.4 

15,720 

3.05 

6.84 

1.79 

22.0 

15,670 

2.26 

7.29 

1.69 

20.9 

15,730 

2.60 

6.96 

1.53 

21.0 

15,710 

2.80 

8.94 

0.88 

19.0 

15,630 

Somerset  Co.,  Pa.,  run-of-mine 

2.56 

9.39 

0.93 

18.7 

15,610 

(73,000  tons) 

2.89 

7.76 

1.31 

24.5 

15,630 

Clearfield  Co.,  Pa.,  run-of-mine 

2.63 

10.09 

15,810 

W.  Salisbury,  Pa.,  run-of-mine 

3.16 

6.12 

'  0.68 

'  20.  'l  ' 

15,720 

Pocahontas  and  New  River,  W.  Va. 

2.14 

4.73 

1.01 

23.4 

15,650 

New  River,  Fayette  Co.,  W.  Va. 

3.03 

5.24 

0.66 

22.2 

15,790 

Pocahontas,  Va.,  Big  Vein 

2.63 

5.25 

0.64 

19.8 

15,770 

Pocahontas,  run-of-mine  (407,000  tons) 

2.36 

7.38 

0.81 

20.6 

15,660 

Thin  Bed,  near  Welch,  Va. 

3.08 

4.57 

0.66 

19.0 

15,770 

Mercer      and       McDowell 

Cos.,  W.  Va. 

2.22 

4.92 

0.84 

23.6 

15,670 

New  River,  Fayette  Co.,  W.  Va. 

2.07 

5.34 

0.72 

21.6  • 

15,730 

Pocahontas  and  New  River 

EASTERN   BITUMINOUS. 


4.07 

9.21 

1.86 

37.8 

15,230 

3.18 

6.85 

0.92 

34.0 

15,500 

3.19 

6.66 

0.98 

33.5 

15,360 

3.59 

10.83 

1.33 

36.2 

15,120 

.44 

8.29 

1.38 

36.7 

15,180 

.82 

6.59 

1.24 

38.8 

15,270 

.07 

7.67 

1.50 

31.8 

15,490 

.26 

6.45 

1.55 

31.5 

15,610 

.90 

4.58 

1.05 

35.1 

15,380 

Elk  and  Jefferson  Cos.,  Pa.,  Lower  Free- 
port  bed 
Kanawha  Gas  Coal,  Powelton  bed.W.V. 

Monogahela  R.,  Pa.,  Pittsburgh  bed 
Youghiogheny  River,  Pa. 
Westmoreland  Co.,  Pa.,  thin  vein. 
Pratt  City,  Ala.,  Pratt  bed 

Blocton,  Ala.,  Cataba  red  ash 


WESTERN   BITUMINOUS. 


6.76 

11.05 

2.37 

41.7 

14,490 

Pana,  111.,  No.  6  bed,  washed  nut 

7.08 

9.38 

2.19 

41.8 

14,550 

10.89 

12.38 

3.90 

48.1 

14,110 

Staunton,  111.,  No.  6  bed,  lump 

3.28 

10.66 

4.28 

39.6 

15,000 

Cherokee  and  Crawford  Cos.,  Kansas, 

lump 

8.30 

14.21 

3.76 

42.6 

14,470 

Englevale,  Kans.,  Cherokee  run-of-mine 

3.87 

12.67 

0.72 

42.5 

14,760 

Las  Animas  Co.,  Colo. 

COAL.  89 

Purchase,  by  Thermal  Value.* — Some  of  the  largest  central  stations 
and  private  corporations  have  adopted  as  a  basis  of  coal  purchase 
specifications  involving  the  thermal  values  of  the  fuel.  A  specification 
typical  of  this  class  reads  as  follows : 

I.  The  company  agrees  to-  furnish  and  deliver  to  the  consumer 

at  such  times  and  in  such  quantities  as  ordered 

by  the  consumer  for  consumption  at  said  premises  during  the  term 
hereof,  at  the  consumer's  option,  either  or  all  of  the  kinds  of  coal 
described  below;  said  coals  to  average  the  following  assays: 

KIND  OF  COAL. 

Of  size  passing  through  screen  having  circular  perforations  in 

diameter — in. — in. — in. 

Of  size  passing  over  a  screen  having  circular  perforations  in 

diameter — in. — in. — in. 

Per  cent  of  moisture  in  coal  as  delivered —      —      — 

Per  cent  of  ash  in  coal  as  delivered —      —      — 

B.T.U.  per  pound  of  dry  coal — 

From  following  county '....- 

From  following  State ' - 

Coal  of  the  above  respective  descriptions  and  specified  assays 
(not  average  assays)  to  be  hereinafter  known  as  the  contract  grade 
of  the  respective  kinds. 

II.  The  consumer  agrees  to  purchase  from  the  company  all  of 
the  coal  required  for  consumption  at  said  premises  during  the  term 
of  this  contract,  except  as  set  forth  in  paragraph  III  below,  and 
to  pay  the  company  for  each  ton  of  2000  pounds  avoirdupois  of 
coal  delivered  and  accepted  in  accordance  with  all  of  the  .terms 
of  this  contract  at  the  following  contract  rate  per  ton  of  each  re- 
spective contract  grade,  at  which  rates  the  company  will  deliver  the 
following  respective  numbers  of  British  thermal  units  for  one 
cent,  the  contract  guarantee. 

Kind  of  Coal.  Contract  Rate  per  Ton.  Contract  Guarantee. 

$ Equal  to net  B.T.U.  for  Ic. 

$ Equal  to net  B.T.U.  for  Ic. 

$ Equal  to net  B.T.U.  for  Ic. 

Said  net  B.  T.  U.  for  one  cent  being  in  each  case  determined 
as  follows :  Multiply  the  number  of  B.  T.  U.  per  pound  of  dry 
coal  by  the  per  cent  of  moisture  (expressed  in  decimals),  subtract 
the  product  so  found  from  the  number  of  B.  T.  U.  per  pound  of 
dry  coal ;  multiply  the  remainder  by  2000  and  divide  this  product 
by  the  contract  rate  per  ton  (expressed  in  cents)  plus  one-half  of 
the  ash  percentage  (expressed  as  cents). 

*  J.  E,  We>odwell,  Proc.  Am.  Soc.  for  Testing  Materials,  1907. 


90  STEAM-BOILER  ECONOMY. 

III.  It  is  provided  that  the  consumer  may  purchase  for  consump- 
tion  at   said   premises   coal   other   than   herein   contracted   for   for 
test  purposes,  it  being  understood  that  the  total  of  such  coal  so 
purchased,  shall  not  exceed  five  per  cent  of  the  total  consumption 
during  the  term  of  this  contract. 

IV.  It  is  understood  that  the  company  may  deliver  coal  here- 
under  containing  as  high  as  three  per  cent  more  ash  and  as  high 
as  three  per  cent  more  moisture  and  as  low  as  500  fewer  B.  T.  U. 
per  pound  dry  than  specified  above  for  contract  grades. 

V.  Should  any  coal  delivered  hereunder  contain  more  than  the 
per  cent  of  ash  or  moisture  or  fewer  than  the  number  of  B.  T.  U. 
per  pound  dry  allowed  under  paragraph  IV  hereof,  the  consumer 
may,  at  its  option,  either  accept  or  reject  the  same. 

VI.  All  coal  accepted  hereunder  shall  be  paid  for  monthly  at  a 
price  per   ton   determined   by   taking  the   average   of   the   delivered 
values  obtained  from  the  analyses  of  all  the  samples  taken  during 
the  month,  said  delivered  value  in  each  case  being  obtained  as  fol- 
lows :     Multiply  the  number  of   B.   T.   U.   delivered   per  pound  of 
dry  coal  by  the  per  cent  of  moisture  delivered  (expressed  in  decimals) ; 
subtract  the  product  so  found  from  the  number  of  B.   T.  U.   de- 
livered  per  pound   of   dry   coal;   multiply   the   remainder   by   2000 
and  divide  this  product  by  the  contract  guarantee ;  from  the  quo- 
tient (expressed  as  dollars  and  cents)   subtract  one-half  of  the  ash 
percentage  delivered   (expressed  as  cents). 

Another  form  of  this  kind  in  force  at  this  time  and  even  more 
rigid  in  many  particulars  as  applying  to  a  particular  kind  of  coal 
virtually  specified  is  of  especial  interest  as  indicating  a  full  apprecia- 
tion of  the  financial  importance  of  safeguarding  the  interests  of 
large  consumers  in  the  effort  to  secure  the  best  thermal  return 
for  the  expenditure.  The  contract  requirements  are  drawn  with 
a  view  to  procuring  a  definite  kind  of  coal  described  as  a  "good 
steam,  coking,  run-of-mine,  bituminous  coal,  free  from  all  dirt  and 
excessive  dust,  a  dry  sample  of  which  will  approximate  the  com- 
pany's standard  in  the  heat  value  and  analysis,  as  follows" : 

Carbon 71  per  cent 

Volatile  matter 20 

Ash 9 

100       " 

Sulphur 1.5   " 

B.T.U 14,000 

The  price  paid  by  the  company  per  ton,  for  a  lighter  of  coal,  is 
based  upon  a  table  of  heat  values  for  excess  or  deficiency  of  its 
standard.  This  table  places  the  arbitrary  valuation  of  1  per  cent 


COAL.  91 

for  each  50  B.  T.  U.  excess  of  deficiency.  (If  this  table  is  calculated 
in  direct  proportion  to  the  price  of  the  coal,  that  price  would  evidently 
be  $2.80.)  In  addition  to  the  corrections  for  heating  value  as 
determined  by  a  Mahler  bomb  calorimeter,  the  price  paid  is  sub- 
ject to  deductions  for  excess  of  ash,  volatile  matter,  sulphur  or 
dust,  or  for  a  shortage  in  the  standard  lighter  quantity. 

Volatile  matter  and  ash  are  each  penalized  to  the  extent  of 
two  cents  per  ton  for  each  one-half  of  1  per  cent  above  the  standard, 
while  excess  of  sulphur  is  penalized  to  the  extent  of  six  cents  per 
ton  for  the  first  quarter  of  1  per  cent  excess  and  four  cents  per 
ton  for  each  succeeding  quarter  of  1  per  cent  up  to  2.5  per  cent,  above 
which  a  deduction  of  twenty  cents  per  ton  is  made.  A  further 
deduction  of  seven  cents  per  ton  is  made  if  any  lighter  of  coal 
delivered  at  the  company's  docks  contains  less  than  700  tons. 

With  the  respect  of  business  clauses  the  contract  is  carefully 
drawn,  and  such  subjects  as  bond,  payments,  deliveries,  docking, 
towing  and  demurrage,  and  method  of  sampling,  testing  and  arbi- 
trating test  results  are  all  explicitly  covered.  The  amount  of  coal  con- 
sumed by  this  company,  over  350,000  tons  per  annum,  valued  at  about 
a  million  dollars,  fully  justifies  such  elaborate  contract  conditions. 

Coal  Specifications  of  Street  Railway  Companies. — In  the  coal 
specifications  of  the  Cleveland  Railway  Company  the  standard  for 
heat  value  per  pound  of  dry  coal  is  12,610  to  12,759  B.T.U.,  inclu- 
sive. The  premiums  range  upon  a  graded  scale  as  high  as  21  cents 
per  ton  above  standard  price  for  heat  values  of  13,960  B.T.U.  and 
above;  whereas  the  penalties  range  as  high  as  50  cents  per  ton  for 
heat  values  of  10,660  to  10,809. 

The  standard  for  ash  is  placed  at  from  0  to  15  per  cent,  with  no 
premium  for  a  minimum  amount.  For  excess  ash,  however,  the 
penalty  reaches  50  cents  per  ton  for  29.1  per  cent  and  over.  Like- 
wise a  heavy  penalty  is  provided  for  sulphur.  The  standard  is  placed 
at  from  0  to  3.5  per  cent  and  the  penalty  increases  gradually  until 
it  is  45  cents  per  ton,  corresponding  to  10  per  cent  and  over. 

It  is  further  stipulated  that  if  the  contractor  should  fail  at  any 
time  to  supply  coal  of  such  quality  or  quantity  as  stipulated  in  the 
contract,  the  railway  company  shall  have  the  right  to  purchase  coal 
in  such .  quantities  as  may  be  needed,  at  the  market  rates  and  in  the 
open  market,  and  collect  the  additional  cost,  if  there  be  any,  from 
the  contractor.  Also,  the  railway  company  shall  have  the  right  to 
cancel  the  contract  and  relet  the  work  should  the  contractor  fail  to 
fulfil  all  the  terms  of  the  contract. 

The  specifications  of  the  Interborough  Rapid  Transit  Company 
provide  for  the  acceptance,  without  penalty,  of  coal  containing  20 


92  iSTEAM-BOILER  ECONOMY. 

per  cent  or  less  volatile  matter,  9  per  cent  or  less  ash  and  1.5  per  cent 
or  less  sulphur.  This  is  designated  as  the  standard  with  no  pre- 
miums for  minimum  amounts,  but  with  penalties  ranging  as  high  as 
18  cents  a  ton  for  24  per  cent  or  more  volatile  matter,  23  cents  per 
ton  for  13.5  per  cent  or  more  ash,  and  12  cents  per  ton  for  sulphur 
up  to  2.5  per  cent.  The  premiums  for  an  excess  in  B.T.U.  over  the 
standard  of  14,201  to  14,250  run  as  high  as  26  cents  per  ton  for 
15,505  B.T.U.  per  pound  of  dry  coal  and  the  maximum  penalty  is 
45  cents  per  ton  for  a  heat  value  of  12,000  B.T.U.  or  less  per  pound 
of  dry  coal.  The  average  premium  and  penalty  is  about  1  cent  per 
ton  for  each  50  B.T.U.  in  excess  or  short  of  the  standard. — Power, 
Oct.  17,  1911. 

The  Purchase  of  Coal.* — When  coals  of  the  same  character  are 
under  consideration  the  heating  value  may  be  considered  as  a  correct 
measure  of  the  value  of  the  coal.  When  coals  of  different  character 
are  to  be  compared,  the  character  of  the  coal  as  well  as  the  heating 
value  must  be  considered. 

There  is  often  a  considerable  variation  in  the  quality  of  coals 
from  the  same  district,  due  principally  to  impurities  in  the  coals  or 
in  the  methods  of  mining  and  preparing  the  coals  for  the  market. 

It  is  a  common  practice  for  one  company  to  operate  a  number  of 
mines  and  to  ship  coal  from  all  of  these  mines  to  their  customers.  It 
is  rarely  that  coal  is  equally  good  in  all  the  mines  and,  therefore, 
the  customer  will  receive  some  good  coal  and  some  inferior.  It  is 
not  practicable  in  many  cases  to  furnish  the  coal  from  one  mine. 

Some  coals  may  be  burned  at  either  high  or  low  rates  of  combus- 
tion without  difficulty  and  with  good  efficiency,  but  there  are  many 
coals  which  always  give  trouble  from  clinker  when  burned  at  high 
rates  of  combustion.  When  burned  at  moderate  rates  they  may 
usually  be  fired  so  as  to  give  the  same  percentage  of  heat  to  the 
boiler  as  the  non-clinkering  coals. 

The  influence  of  the  volatile  matter  on  the  efficiency  depends  on 
the  design  of  the  furnace.  With  a  poor  furnace  and  indifferent  firing 
coals  containing  about  18%  volatile  matter  may  give  results  10  or  12% 
higher  than  coals  containing  30%  or  more  volatile  matter. 

As  there  is  a  loss  of  both  time  and  heat  while  the  fires  are  being 
cleaned  the  presence  of  large  quantities  of  ash  interferes  with  the 
proper  distribution  of  air  through  the  fuel  and  may  lower  the  ef- 
ficiency. 

The  moisture  not  only  requires  heat  to  evaporate  it  into  steam, 
but  if  the  coal  is  very  wet  and  is  fired  in  large  quantities,  it  may  cool 
the  bed  of  fire  and  cause  an  additional  loss  of  unburned  gas. 

The  size  of  coal  is  important  in  many  cases.  If  the  coal  does 
not  coke  and  is  fine,  there  may  be  a  large  loss  of  fuel  through  the 
grates  when  burned  on  inclined  grate  stokers  or  on  hand-fired  grates 

*  Extracts  from  a  paper  by  Dwight  T.  Randall,  in  Jour.  A.  S.  M.  E.,  March, 
1910. 


COAL.  93 

at  rates  that  require  frequent  breaking  up  of  the  fuel  bed.  If  coal  is 
too  large  more  air  is  admitted  than  is  necessary  to  burn  it  properly 
and  if  the  fuel  bed  cannot  be  increased  in  thickness  to  overcome  this 
difficulty,  there  will  be  a  large  heat  loss.  If  the  coal  is  fine  and  the 
draft  is  very  strong,  some  of  it  will  be  carried  off  the  grate  only  par- 
tially burned. 

Fine  coal  which  cakes  and  forms  a  porous  coke  may  be  burned 
with  good  efficiency.  If  the  coal  does  not  coke  but  packs  closely  on 
the  fuel  bed,  it  is  difficult,  if  not  impossible,  to  secure  a  uniform  air 
supply  at  all  parts  of  the  bed  and  the  combustion  is  poor  owing  to 
an  excess  of  air  at  some  points  and  a  lack  of  air  at  others. 

It  has  been  found  possible  to  design  furnaces  to  burn  almost  any 
fuel  with  reasonably  good  efficiency  based  upon  the  available  heat  of 
the  fuel.  This  has  been  accomplished  with  tan  bark,  sawdust,  lignite 
and  low  grade  coals.  As  a  rule  inferior  coals  can  be  bought  much 
more  cheaply  on  their  heating  value  than  the  higher  grades  of  coal. 
In  many  cases  it  will  be  profitable  to  change  the  equipment  so  as  to 
burn  slack  coal  or  coals  which  are  below  the  average  quality.  It  is 
fully  as  important  to  take  into  account  the  size  and  character  of  coal 
when  automatic  stokers  are  in  use  as  when  the  coal  is  hand-fired. 

The  coal  dealer  should  not  be  held  responsible  for  results  in 
boiler  plants  except  as  influenced  by  changes  in  the  quality  of  the 
coal  delivered.  A  coal  which  is  suited  to  one  plant  may  not  burn  well 
in  another,  owing  to  differences  in  equipment,  load  condition  or  to 
the  methods  of  handling  the  fires. 

The  method  of  taking  a  sample  of  coal  is  fully  as  important 
as  the  manner  in  which  it  shall  be  analyzed  and  the  cause  of  doubt 
as  to  the  value  of  coal  analyses  has  been  largely  due  to  ignorance  or 
carelessness  in  taking  samples  for  analysis. 

Methods  of  Sampling. — The  following  method  of  obtaining  a 
sample  of  coal  has  been  used  by  a  number  of  different  firms  and  has 
been  found  satisfactory.  The  object  in  taking  a  sample  is  to  secure 
a  small  portion  of  the  coal  which  represents  as  nearly  as  possible  the 
entire  shipment  or  delivery. 

The  original  sample  should  preferably  be  collected  in  a  large 
receptacle  with  cover  attached,  by  taking  small  shovelfuls  from  many 
parts  of  the  car,  barge  or  vessel  as  it  is  being  unloaded,  or  from  as 
nearly  all  parts  of  a  pile  as  possible,  care  being  taken  in  all  cases  to 
secure  practically  the  same  amounts  from  the  top,  middle  and  bot- 
tom of  the  coal.  The  original  sample  thus  taken  should  amount  to 
500  Ibs.  or  more,  preferably  1000  to  2000  Ibs.  A  separate  sample 
should  be  taken  from  each  1000  tons  or  less  delivered.  The  gross 
sample  thus  collected  should  contain  the  same  proportion  of  lump 
and  fine  coal  as  exists  in  the  whole  shipment.  It  should  be  protected 
from  the  weather  in  order  to  avoid  gain  or  loss  in  moisture  and 
should  be  immediately  quartered  down  to  a  smaller  sample,  according 
to  the  following  method. 


94  STEAM-BOILER  ECONOMY. 

The  large  lumps  should  be  broken  down  on  a  clean,  hard,  dry 
floor  with  a  suitable  maul  or  sledge.  The  coal  should  be  thoroughly 
mixed  by  shoveling  it  over  and  over  and  formed  in  a  conical  pile. 
The  pile  should  then  be  quartered,  using  a  shovel  or  board  to  separate 
the  four  quarters.  Two  opposite  quarters  should  then  be  rejected 
and  the  remaining  two  broken  down  to  a  smaller  size,  mixed  and 
re-formed  in  a  conical  pile  and  quartered  as  before.  This  process 
should  be  continued  until  the  lumps  are  %  in.  in  size  or  smaller  and 
a  one  or  two-quart  final  sample  remains.  All  of  this  final  sample 
should  immediately  be  placed  in  one  or  more  glass  or  metal  cans  and 
sealed  air  tight.  The  following  table  gives  the  largest  sizes  allowable 
in  the  samples  of  various  weights  and  the  coal  should  preferably  be 
broken  into  still  smaller  sizes  before  quartering : 

•:f    . 
Weight  of  Sam^fc  Should  pass  through 

1000  Ib.  or  over;!  .  . .  vil lj-in.  sieve 

500  Ib.  oroisyer l^-in.  sieve 

250  Ib.  or  over 1  -in.  sieve 

125  Ib.  or  over f-in.  sieve 

60  Ib.  or  over £-in.  sieve 

10  Ib.  or  over £-in.  sieve 

.L. .. 

The  sample  should  be  worked  down  as  rapidly  as  possible  to 
avoid  loss  of  moisture  through  exposure  to  the  air.  The  outside  of 
the  ..can  should  be  plainly  marked  and  a  corresponding  description 
placed  inside  the  can. 

:  A  sample  of  coal,  taken  by  an  approved  method  and  analyzed  by 
an  experienced  coal  chemist,  should  show  results  which,  when  com- 
pared- with  the  true  values,  are  within  the  following  limits: 

Moisture 1.00  per  cent  of  the  coal  as  delivered 

Ash  +  or  — 0.50  per  cent  of  the  dry  coal 

i.£.l     Sulphur  +  or  — 0.10  per  cent  of  the  dry  coal 

B.t.u.  -f  or  — 1.00  per  cent  of  the  dry  coal 

The  results  will  be  sufficiently  accurate  for  commercial  purposes 
and  within  the  limits  of  error  of  the  weights  of  the  coal  shipped. 
,  The  important  items  in  a  specification  are  as  follows: 

(.a)   A  statement  of  the  amount  and  character  of  the  coal  desired. 

(5)   A  statement  regarding  the  conditions  for  delivery  of  coal. 

(c)  A  statement  regarding  the  disposition  which  will  be  made  of 
the  coal  in  case  it  is  outside  the  limits  specified. 

(d)  A  statement  regarding  the  corrections  in  price  for  variations 
in  heating  value,  in  ash  and  in  sulphur. 

(e)  A  blank  form  on  which  the  dealer  may  submit  the  price  and 
the  kind  and  quality  of  coal  which  he  proposes  to  furnish. 

It  is  necessary  in  almost  every  case  to  modify  the  specifications 
to...  fit  the  special  conditions  in  the  plant  and  the  fuel  which  are 
available. 


COAL. 


95 


The  importance  of  testing  coal  purchased  under  contract  may 
be  illustrated  by  two  recent  cases.  In  Case  1  the  coal  was  guaranteed 
to  be  Georges  Creek  and  in  Case  2  to  be  New  River. 


CAP 

E    1. 

CAS 

E    2. 

Guaranteed 
Analysis  as 
Delivered. 

Coal 

Delivered. 

Guaranteed 
Analysis  as 
Delivered. 

Coal 
Delivered. 

Ash  in  dry  coal. 

8.00 

12.66 

6  00 

8  48 

B.T.U.  in  dry  coal..  .  . 

14,250 

13,558 

14,700 

13,981 

This  method  of  purchasing  coal  has  been  adopted  by  many  of  the 
larger  and  most  progressive  consumers  of  coal.  Its  advantages  are 
so  clearly  demonstrated  to  engineers  experienced  in  power  house 
practice  that  few  who  are  in  a  position  to  purchase  large  -quantities 
of  coal  are  willing  to  do  so  without  a  guarantee  as  to  its  quality. 
With  information  as  to  the  coal  bed,  the  district  and  the  mine  from 
which  the  coal  will  be  furnished  and  the  guaranteed  analysis,  an  ex- 
perienced engineer  can  select  a  coal  for  the  plant  which  is  both  suitable 
and  cheap  when  quality  and  price  are  considered. 

Spontaneous  Combustion  of  Coal.*  — Dust  is  a  dangerous  tning 
in  a  coal  pile,  particularly  if  it  is  mixed  with  larger-sized  coal 
which  forms  air  passages  to  the  interior.  Spontaneous  combustion 
is  brought  about  by  slow  oxidation  in  an  air  supply  sufficient  to 
support  the  oxidation,  but  insufficient  to  carry  away  all  the  heat 
formed.  There  is  a  wide  variation  among  coals  in  friability.  This 
is  a  large  factor  in  spontaneous  combustion.  Mixed  lump  and  fine, 
i.  e.,  run-of-mine,  with  a  large  percentage  of  dust,  and  piled  so  as 
to  admit  to  the  interior  a  limited  supply  of  air,  make  ideal  condi- 
tions for  spontaneous  heating. 

High  volatile  matter  does  not  of  itself  increase  the  liability  to 
spontaneous  heating. 

Pocahontas  coal  gives  a  great  deal  of  trouble  with  spontaneous 
fires  in  the  large  storage  piles  at  Panama.  It  is  reported  by  large 
by-product-coke  concerns  to  be  more  troublesome  in  this  respect 
than  high-volatile  gas  coals.  The  high-volatile  coals  of  the  west 
are  usually  very  liable  to  spontaneous  heating,  but  they  owe  this 


*  Technical  Paper  No.  16,  U.  S.  Bureau  of  Mines,  1912.    II,  C.  Porter  and 
F.  K.  Qvitz, 


96  STEAM-BOILER  ECONOMY. 

property  to  the  chemical  nature  of  the  substances  which  compose  the 
coal  rather  than  to  the  amount  of  volatile  matter.  A  high-oxygen 
content  in  coal  appears  to  promote  its  tendency  to  spontaneous 
combustion. 

The  influence  of  moisture  and  that  of  sulphur  upon  spontaneous 
heating  of  coal  are  questions  not  yet  settled.  Observation  by  the 
Bureau  of  Mines  in  many  actual  cases  has  not  developed  any  instances 
where  moisture  could  be  proven  to  promote  heating.  Sulphur, 
on  the  other  hand,  has  been  shown  to  have,  in  most  cases,  only  a 
minor  influence.  On  the  other  hand,  a  Boston  company,  using  Nova 
Scotia  coal  of  3  to  4  per  cent  sulphur,  has  much  trouble  with  spon- 
taneous fires  in  storage,  but  a  number  of  samples  taken  by  the 
Bureau  from  exposed  piles  of  this  coal  in  which  heating  had  oc- 
curred showed  that  90  per  cent  of  the  sulphur  was  still  unoxidized. 
Experiments  in  the  laboratory,  passing  air  over  coal  at  120  degrees 
centigrade,  have  developed  enough  heat  to  ignite  the  coal  and  no 
change  was  found  in  the  form  of  the  sulphur.  While  not  entirely 
conclusive,  these  results  point  to  a  very  minor  contribution,  if  any, 
on  the  part  of  sulphur  to  spontaneous  heating  in  coal. 

Freshly  mined  coal  and  even  fresh  surfaces  exposed  by  crush- 
ing lump  coal  exhibit  a  remarkable  avidity  for  oxygen,  but  after 
a  time  become  coated  with  oxidized  material,  "seasoned,"  as  it  were, 
so  that  the  action  of  the  air  becomes  much  less  vigorous.  It  is 
found  in  practice  that  if  coal  which  has  been  stored  for  six  weeks 
or  two  months  and  has  even  become  already  somewhat  heated, 
be  rehandled  and  thoroughly  cooled  by  the  air,  spontaneous  heating 
rarely  begins  again. 

With  full  appreciation  of  the  fact  that  any  or  all  of  the  follow- 
ing recommendations  may  under  certain  conditions  be  found  im- 
practicable, they  are  offered  as  being  advisable  precautions  for  safety 
in  storing  coal  whenever  their  use  does  not  involve  an  unreasonable 
expense. 

1.  Do  not  pile  over  12  feet  deep  nor  so  that  any  point  in  the 
interior  will  be  over  10  feet  from  an  air-cooled  surface. 

2.  If  possible,  store  only  in  lump. 

3.  Keep  dust  out  as  much  as  possible;  therefore  reduce  handling 
to  a  minimum. 

4.  Pile  so  that  lump  and  fine  are  distributed  as  evenly  as  possible ; 
not,  as  is  often  done,  allowing  lumps  to  roll  down  from  a  peak 
and  form  air  passages  at  the  bottom. 


COAL.  97 

5.  Eehandle  and  screen  after  two  months. 

6.  Keep   away  external   sources   of  heat  even  though  moderate 
in  degree. 

7.  Allow  six  weeks'  "seasoning"  after  mining  before  storing. 

8.  Avoid  alternate  wetting  and  drying. 

9.  Avoid  admission  of  air  to  interior  of  pile  through  interstices 
around   foreign   objects   such   as   timbers   or   irregular   brick   work; 
also  through  porous  bottoms  such  as  coarse  cinders. 

10.  Do  not  try  to  ventilate  by  pipes,  as  more  harm  is  often  done 
than  good. 


CHAPTER  IV. 
COAL-FIELDS   OF   THE   UNITED  STATES. 

THE  accompanying  maps  showing  the  developed  coal-fields  of  the 
United  States  are  copied  from  one  that  was  published  in  the  Reports 
of  the  Census  of  1890. 

The  long  field  extending  southwesterly  from  north-central  Penn- 
sylvania to  near  the  centre  of  Alabama  is  the  great  Appalachian  field, 
which  contains  in  a  narrow  strip  on  its  eastern  border  the  semi- 
bituminous  coals,  and  west  of  this  strip  the  best  varieties  of  bituminous 
gas,  steam,  and  coking  coals..  East  of  this  field  there  are  several 
small  detached  fields,  the  most  important  of  which  are  the  three  an- 
thracite fields  of  eastern  Pennsylvania.  To  the  northwest  there  is  the 
separate  field  of  Michigan,  containing  a  rather  poor  quality  of  bitumi- 
nous coal.  To  the  west  is  the  Illinois  or  Central  field,  extending  into 
Indiana  and  Kentucky,  and  containing  a  great  variety  of  bituminous 
coals,  most  of  which  are  inferior  to  the  coals  of  the  Appalachian  field. 
West  of  the  Mississippi  the  principal  field  is  the  great  Missouri  field 
covering  several  States,  and  having  several  detached  portions  reaching 
into  Texas.  The  coals  of  this  field  are  mostly  of  a  poor  quality.  West 
of  the  97th  meridian  there  are  a  great  number  of  detached  fields,  mostly 
of  small  areas,  with  every  grade  of  coal  from  anthracite  to  lignite. 
The  principal  characteristics  of  the  several  fields,  and  the  quality  of  the 
coal  found  in  each,  will  be  treated  of  below. 

Graphitic  Coal  in  Rhode  Island  and  Massachusetts. —  An  area  of 
400  square  miles  in  the  central  part  of  Rhode  Island  and  eastern  part 
of  Massachusetts,  from  Newport  Neck,  R.  I.,  to  Mansfield,  Mass.,  con- 
tains a  variety  of  anthracite  which  has  been  metamorphosed  into 
graphite  or  graphitic  coal.  It  requires  a  such  high  degree  of  heat  for 
combustion  that  it  can  be  used  only  with  other  combustible  material  or 
under  a  heavy  draft.  The  deposit  was  worked  as  early  as  1808  at  the 
Porstmouth  mine,  and  at  intervals  since,  but  never  with  profit. 


IgO        127        125         123       121         119        117        US        113 111        109       107       105      103       101       99        97 


119 


COAL-FIELDS  OF  THE  UNITED  STATES  WEST  OF  THE  97TH  MERIDIAN. 


COAL-FIELDS  OF  THE  UNITED  STATES.  99 

ANALYSES   OF  RHODE   ISLAND    AND   MASSACHUSETTS    COAL. 

Water  and  Volatile  Matter.          Fixed  Carbon.          Ash. 

Mansfield,  Mass 2  to    4  90  to  92  4 

Rhode  Island  coal 7  to  10  77  to  84         5  to  6 

Cranston,  R.I 8.55  3.55  82.25  5.65 

The  Anthracite  Coal-beds  of  Pennsylvania. — These  beds  are  all  in 
the  eastern  portion  of  the  State.  They  are  three  in  number,  known 
variously  as  First,  Second,  and  Third,  as  Southern,  Middle,  and 
Northern,  or  as  Schuylkill,  Lehigh,  and  Wyoming.  The  area  of  the 
first  is  143  square  miles,  of  the  second  128  square  miles,  and  of  the 
third  198  square  miles — a  total  of  469  square  miles.  There  are  fifteen 
workable  beds  in  this  area,  of  a  total  thickness  of  107  ft.  of  coal,  the 
thickness  of  the  measures  in  which  the  beds  are  interstratified  being 
about  3000  feet.  The  coal  in  all  of  the  fields  follows  the  general  law 
of  increasing  in  percentage  of  volatile  matter  and  decreasing  in  hard- 
ness towards  the  western  portion  of  the  fields. 

In  "Mineral  Resources"  for  1886  the  anthracite  fields  of  Penn- 
sylvania are  described  as  grouped*  into  five  principal  divisions: 
( 1 )  The  southern  or  Pottsville  field,  extending  from  the  Lehigh  River 
at  Mauch  Chunk  southwest  to  within  a  few  miles  of  the  Susquehanna 
River  north  of  Harrisburg;  (2)  the  western  or  Mahanoy  and  Shamokin 
field,  lying  between  the  eastern  head-waters  of  the  Little  Schuylkill 
River  and  the  Susquehanna;  (3)  the  eastern  middle  or  the  upper 
Lehigh  field,  lying  between  the  Lehigh  River  and  Catawissa  Creek, 
principally  in  Luzerne  County;  (4)  the  northern  or  Wyoming  and 
Lackawanna  field,  which  lies  in  the  two  valleys  from  which  its  geo- 
graphical name  is  derived;  (5)  the  Loyalsock  and  Mehoopany  field, 
named  from  the  two  creeks  whose  head-waters  drain  it.  The  latter  is 
a  small  field  about  20  or  25  miles  northwest  of  the  western  end  of  the 
northern  field. 

In  addition  to  this  geological  division  the  fields  are  also  subdivided 
under  different  names  and  in  a  different  way  for  trade  purposes,  the 
divisions  being  known  as  trade  regions.  These  are  •  ( 1 )  The  Wyoming 
region,  embracing  the  entire  northern  and  Loyalsock  fields;  (2)  the 
Lehigh  region,  embracing  all  of  the  eastern  middle  field  and  the  Pan- 
ther Creek  district  of  the  southern  field;  and  (3)  the  Schuylkill  region, 
embracing  the  western  middle  field  and  all  of  the  southern  field  except 
the  Panther  Creek  district. 

Size  and  Quality  of  Anthracite  (Paul  Sterling,  Trans.  Am.  Inst. 
Mining  Engrs.,  1911) — The  following  table  gives  the  various  sizes,  the 


IUU 


STEAM-BOILER  ECONOMY. 


diameter  of  ring  over  and  through  which  each  size  is  made,  and  the 
usual  purpose  for  which  it  is  employed. 

COMMERCIAL  SIZES  OF  ANTHRACITE. 


Name. 

Diameter  of  Ring. 

Use. 

Over. 

Through. 

Lump 

Inches. 

VA 

±1A 

VA 

2A 

lu 

1 
i 

Inches. 

Locomotive  steam  coal 
Blast-furnaces;   smiths'  forges 

Domestic  furnace-coal 

t  i            it 

Domestic  range-coal 

11           1  1 

Domestic  furnace-coal 
Boiler,  steam 

Steamboat 

VA 

VA 
VA 

1 

!| 

X    1 

Broken  

Egg  

Stove.  . 

Nut  

Pea  

Buckwheat  
Rice  
Barley  

The  following  table  gives  a -standard  of  preparation  which  is  about 
the  average  adopted  in  the  anthracite  coal-field.  The  table  allows 
a  percentage  of  "bone,"  in  addition  to  slate,  in  the  coal ;  "bone"  being 
defined  as  a  product  containing  between  40  and  55  per  cent  of  carbon. 


STANDARD   OF   PREPARATION,   SHOWING  THE   PERCENTAGE   OF   SLATE,    BONE,    ETC., 
PERMITTED   IN  EACH   SIZE   OF   COAL. 


May  Contain. 

Broken. 

Egg. 

Stove.  . 

Nut. 

Pea. 

Buck. 

Rice. 

Barley. 

Of  slate  

1 

2 

2  5 

4 

8 

10 

15 

15 

Of  bone   

2 

2 

4 

5 

5 

Of  next  size  larger  .  . 

5 

5 

10 

5 

8 

8 

8 

Of  next  size  smaller  < 

20 

50 

50 

15 

15  B. 
15  R. 

15 

25 

Semi-anthracite  in  Sullivan  Co.,  Pa, — The  Bernice  coal-basin  lies 
between  Beech  Creek  on  the  north  and  Loyalsock  Creek  on  the  south. 
It  is  six  miles  long  E.  to  W.,  and  hardly  a  third  of  a  mile  across. 
There  is  8  ft.  of  coal  in  a  bed  of  12  ft.  of  coal  and  slate.  The  coal  of 
this  bed  is  on  the  dividing  line  between  anthracite  and  semi-anthra- 
cite, and  is  similar  to  the  coal  of  the  Lykens  Valley  district.  Nine 
analyses  give  a  range  as  follows:  Water,  0.65  to  1.97;  volatile  matter, 
3.56  to  9.40;  fixed  carbon,  82.52  to  89.39;  ash,  3.27  to  9.34;  sulphur, 
0.24  to  1.04.  More  recent  analyses  (Trans.  A.  I.  M.  E.  xiv,  721)  give 
the  following : 


COAL-FIELDS  OF  THE  UNITED  STATES. 

SULLIVAN   CO.,    PA.,    COAL. 


101 


Water. 

Vol.  Matter. 

Fixed  C. 

Ash. 

Sulphur. 

Working  seam  

0.65 

9.40 

83.69 

5.34 

0.91 

60  feet  below  seam 

3  67 

15  42 

71  34 

8  97 

0  59 

The   first   is   a   semi-anthracite,   the   second   a   semi-bituminous. 

Progression  from  Bituminous  to  Anthracite. — In  a  direction  across 
the  basins  northward  from  Bernice,  in  Sullivan  Co.,  to  Gaines,  in 
Tioga  and  Potter  counties,  a  distance  of  50  miles,  is  seen  the  transi- 
tion from  bituminous  to  anthracite  coal,  the  proportion  of  volatile 
matter  to  fixed  carbon  in  the  different  basins  being: 


Volatile 
Matter. 

Fixed 
Carbon 

G  sines 

1  to    1  964,  equal  to  

33.7 

66.3 

Blossburg 

1  "     3  494,        '  '       

22.3 

77.7 

1  "    4  094         " 

19  6 

80  4 

Bernice 

1  "10  289         '  ' 

8  9 

91  1 

At  Bernice  a  semi-bituminous  coal  underlies  the  semi-anthracite 
60  ft.,  both  beds  being  found  in  the  same  hillside  only  60  ft.  apart.* 
In  another  case  a  coal-bed  has  two  benches,  the  uppei  semi-bitu- 
minous and  the  lower  anthracite,  with  6  ft  of  slate  bottom.  (From 
reports  of  Second  Geological  Survey  of  Pennsylvania.) 

Early  Use  of  Pennsylvania  Anthracite  Coal.— Pennsylvania  anthra- 
cite coal  was  known  as  early  as  1766,  and  was  used  in  1768  in  the 
Wyoming  Valley  by  two  blacksmiths  named  Gore.  In  1776  several 
boat-loads  were  sent  to  Carlisle,  where  it  was  used  during  the  Revolu- 
tionary War  to  manufacture  arms.  It  was  not  used  for  domestic 
purposes  until  1808,  when  Judge  Jesse  Fell  of  Wilkesbarre  burned  it 
on  an  experimental  grate  of  hickory  withes.  He  then  made  an  iron 
grate,  and  taught  the  people  in  the  vicinity  how  to  make  such  grates. 
In  1793  the  Lehigh  Coal  Mining  Co.  was  formed,  which  some  years 
later  sold  a  quantity  to  the  city  of  Philadelphia  for  the  use  of  a 
steam-engine  at  the  water-works,  then  at  Broad  and  Market  streets, 
but  it  was  not  used  because  it  "could  not  be  burned."  In  1812  Col. 

*  It  will  be  noted  that  this  condition  in  Sullivan  Co.,  Pa.,  is  exactly  opposite 
to  that  found  in  western  Pennsylvania  and  central  Ohio,  where  the  coals  mined 
over  a  large  extent  of  country  show  nearly  identical  composition.  See  Lord  and 
Haas's  tests  in  the  next  chapter. 


102  STEAM-BOILER  ECONOMY. 

George  Shoemaker  took  nine  wagon-loads  to  Philadelphia,  disposed  of 
two  or  three  loads  at  the  cost  of  handling,  and  left  the  rest  with 
different  persons  for  experiment.  At  the  Fairmount  Wire  and  Nail 
Works  the  workmen  spent  a  forenoon  in  fruitless  attempts  to  make 
a  fire  with  it.  At  last  they  closed  the  furnace  doors  and  went  to 
dinner ;  returning  an  hour  later,  they  found  the  doors  red-hot  and  the 
furnace  all  aglow.  After  that  there  was  no  more  trouble  in  burning 
anthracite.  In  1820  the  trade  was  fully  established,  365  tons  being 
shipped  to  Philadelphia  in  that  year. 

The  failures  to  burn  anthracite  in  these  early  days  were  due  to 
ignorance  of  the  proper  conditions  for  burning  it.  These  are: 

1.  A  very  hot  fire  of  wood  must  first  be  established. 

2.  The  coal  should  be  laid  in  a  bed  several  inches  deep. 

3.  The  bed  of  coal  must  not  be  poked  or  otherwise  disturbed 
while  beginning  to  burn. 

4.  A  constant  supply  of  air  must  be  maintained  from  the  grate 
through  the  fire. 

An  interesting  account  of  the  early  history  of  the  anthracite  coal 
trade  will  be  found  in  "Mineral  Industry"  for  1895. 

Virginia  Anthracite. — In  the  southwestern  part  of  Virginia 
occur  beds  of  coal  which  on  analysis  prove  to  be  anthracite.  They 
are  found  in  Pulaski  and  Wythe  counties,  along  the  southern  border 
of  Little  Walker  Mountain.  The  areas  are  limited,  and  the  coals  have 
been  greatly  disturbed.  They  do  not  belong  to  the  true  Carboniferous 
coals,  but  to  the  Upper  Devonian  (Rogers  X.)  formation,  and  lie 
under  the  true  coal-measures  of  Pennsylvania,  Ohio,  and  northwestern 
Virginia. 

Analyses  of  seven  samples  gave : 

Water.  Volatile  Matter.  Fixed  Carbon.  Ash. 

0.35  to  0.80  6  to  7. 58  85. 85  to  89. 47  3. 97  to  7. 35 

Anthracite  in  Colorado. — Anthracite  coal  of  good  quality  is  found 
in  Gunnison  Co.,  Colorado  (Hayden's  Survey  Report  for  1874).  The 
coal  is  not  a  true  Carboniferous  anthracite,  but  is  an  "altered  lig- 
nite" of  the  Post-Cretaceous  formation.  The  quality  varies  greatly  in 
different  beds  and  even  in  the  same  bed  in  neighboring  localities, 
occuring  in  all  stages  of  transition  from  bituminous  to  hard  anthra- 
cite. The  following  are  analyses  of  some  of  these  coals.  No.  Ill 
might  be  classified  as  a  semi-bituminous  coal,  and  No.  VI  as  a  semi- 
anthracite. 


COAL-FIELDS  OF  THE   UNITED  STATES. 


103 


COLORADO    ANTHRACITES. 


I. 

II. 

III. 

IV. 

v. 

VI. 

Water  

2.00 

1.60 

4  00\ 

/    1  64 

Volatile  matter  
Fixed  carbon  
Ash  

2.50 
91.90 
3.60 

3.40 
88.20 
6.80 

14.00J 

74.00 
8.00 

7.40 

88.92 
3.68 

3.68 

91.02 
5.30 

1    7.39 
86.60 
4.37 

Anthracite  in  New  Mexico. — Dr.  R.  W.  Raymond,  formerly  IT.  S. 
Mining  Commissioner,  in  his  report  for  1870  describes  a  bed  of  true 
anthracite,  4  to  5  feet  thick,  near  Santa  Fe,  containing  80.5%  of 
fixed  carbon,  and  another,  1£  miles  distant,  containing  88%  carbon 
and  5%  ash. 

BITUMINOUS  AND   SEMI-BITUMINOUS   COAL-FIELDS   OF  THE  UNITED 

STATES. 

The  following  notes  on  the  bituminous  and  semi-bituminous  coal- 
fields and  on  the  quality  of  coal  found  in  them  have  been  compiled 
from  a  variety  of  sources;  among  others,  the  reports  of  the  U.  S. 
Census  of  1890,  and  annual  volumes  of  "Mineral  Resources  of  the 
United  States"  and  "Mineral  Industry,"  reports  of  the  Geological 
Surveys  of  Pennsylvania  and  other  States,  and  various  papers  in  the 
Transactions  of  the  American  Institute  of  Mining  Engineers. 

The  Triassic  Area  comprises  what  is  known  as  the  Richmond 
basin  in  Chesterfield  and  Henrico  counties,  Virginia,  and  the  Deep 
River  and  Dan  River  fields  in  North  Carolina.  Charles  A.  Ashburner, 
in  "Mineral  Resources"  for  1886,  says  that  the  first  coal  mined 
systematically  in  the  United  States  was  taken  from  the  Richmond 
basin,  and  that  in  1822  about  48,214  tons  of  coal  were  produced  there, 
more  than  twelve  times  the  total  amount  produced  in  the  Pennsyl- 
vania anthracite  field  in  the  same  year.  Its  maximum  output  was 
reached  in  1883,  when  142,587  tons  were  mined. 

The  Bituminous  Coals  of  the  Carboniferous  Formation  (not  in- 
cluding the  more  recent  coals  of  the  Western  States)  are  found  in  four 
separate  fields  or  basins,  which  are  shown  on  the  map,  viz. :  1.  The 
Appalachian  field,  extending  from  Pennsylvania  to  Alabama,  contain- 
ing 59,105  square  miles.  The  eastern  portion  of  the  Appalachian 
field  contains  the  semi-bituminous  Coals,  which  are  found  in  a 
narrow  strip  running  from  northern  Pennsylvania  through  portions 
of  Maryland,  Virginia,  West  Virginia,  and  Tennessee.  2.  The  Illinois 
basin,  extending  into  the  western  part  of  Indiana  and  northwestern 


104'  STEAM-BOILER  ECONOMY. 

Kentucky,  47,188  square  miles.  3.  The  Michigan  basin,  6700  square 
miles.  4.  The  Missouri  or  Western  basin,  90,343  square  miles,  cover- 
ing portions  of  Iowa,  Nebraska,  Missouri,  Kansas,  Indian  Territory, 
and  Arkansas,  with  an  extension  into  Texas.  The  coal  in  this  basin 
is  in' general  not  so  pure  as  that  in  the  Appalachian  field,  and  contains 
a  great  deal  of  sulphur. 

West  of  the  Missouri  there  are  the  lignites  and  lignitic  coals 
(some  of  them  transformed  into  bituminous  and  anthracite)  of  the 
Rocky  Mountain  field,  containing  the  coal  areas  in  the  States  and 
Territories  lying  along  the  Rocky  Mountains,  and  the  Pacific  Coast 
field,  embracing  the  coal  districts  of  Washington,  Oregon,  and  Cali- 
fornia. 

The  various  fields  are  described  at  some  length  in  "Mineral  Re- 
sources" for  1886,  and  also  in  the  report  for  1894.  The  latter  also 
contains  some  historical  information  regarding  the  development  of 
these  fields.  "Mineral  Resources"  for  1892  contain  some  interesting 
contributions  from  State  geologists  on  the  coal-fields  of  several 
States,  and  the  1910  volume  contains  an  excellent  paper  by  E.  W. 
Parker,  "The  Production  of  Coal  in  1910,"  with  maps  of  the  coal- 
fields in  different  States,  descriptions  of  the  fields,  and  a  complete 
list  of  the  publications  of  the  U.  S.  Geological  Survey  relating 
to  coal. 

•Pennsylvania. — -The  Appalachian  coal-field  extends  over  portions 
of  31  counties.  It  has  an  area  of  about  14,200  square  miles  in  the 
State. 

Blossburg  field,  Tioga  Co.  Five  beds,  A,  B,  C,  D,  and  E,  from 
%y2  to  51/2  feet  thick.  Coal  A  is  the  lowest  of  the  series.  Coal  B, 
Bloss  bed  4%  to  5^2  feet,  is  the  best.  Coal  C  is  a  sort  of  a  cannel-coal 
of  an  inferior  grade  in  this  location;  farther  west  it  improves. 

Mclntyre  basin,  Lycoming  Co.  The  coal-beds  are  similar  to  those 
of  the  Blossburg  region,  three  of  them,  E,  C,  and  A,  being  of  work- 
able thickness. 

Towanda  basin,  Bradford  Co.  One  seam  also  found  in  the  Mc- 
lntyre basin. 

Snowshoe  basin,  Centre  Co.  Eight  miles  in  length  by  four  in 
width.  Five  seams.  A  has  6  to  3y2  feet,  and  E  5  feet,  of  good  coal. 

Clearfield  region,  on  Moshannon  Creek,  in  Clearfield  Co.  Three 
workable  seams,  5,  4%,  and  4  feet. 

Johnstown  region,  Cambria  Co.    Five  beds,  2^2  to  7  feet  thick. 


COAL-FIELDS  OF  THE  UNITED  STATES.  105 

Broad  Top  basin,  in  Bedford,  Huntington,  and  Fulton  counties, 
40  miles  east  of  the  Alleghany  Mountains.  The  area  is  81  square 
miles.  Five  workable  beds,  the  principal  one  being  5  to  10  feet  thick. 

Salisbury  basin,  Somerset  Co.  A  short  extension  of  the  Cumber- 
land coal-field  of  Maryland.  It  contains  all  the  coals  of  the  Lower 
measures  and  several  square  miles  of  the  Pittsburg  seam. 

Semi-bituminous  coal  is  produced  in  all  the  above-named  fields. 

Main  Field  of  Western  Pennsylvania.  One  large  field  in  the  south- 
western counties.  The  several  beds  are  found  in  different  series, 
known  respectively  as  the  Upper  Barren,  the  Upper  Productive,  the 
Lower  Barren,  and  the  Lower  Productive  coal-measures,  and  the 
Conglomerate  series.* 

*  The  geologists  have  changed  the  names  of  these  coal  measures,  as  in  the 
following  description,  taken  from  "Mineral  Resources,"  1910. 

The  coal-bearing  rocks  all  belong  to  the  Pennsylvania  series,  and  have  a 
total  thickness  in  the  southwest  corner  of  the  State  of  about  2600  feet.  The 
great  bulk  of  the  coal  mined  comes  from  the  Allegheny  and  the  Monongahela 
formations,  formerly  known  as  the  "Lower"  and  the  "Upper  Productive  Coal 
Measures."  Below  the  Allegheny  formation  is  the  Pottsville,  containing,  in  the 
western  part  of  the  State,  the  Sharon  and  the  Mercer  coals,  which  have  been 
worked  only  in  restricted  areas.  The  Allegheny  formation,  with  a  thickness  of 
250  to  350  feet,  contains  at  least  seven  coal  horizons,  all  of  which  yield  workable 
coal  locally.  They  are  called,  beginning  at  the  bottom,  the  Brookville,  Clarion, 
Lower  Kittanning,  Middle  Kittanning,  Upper  Kittanning,  Lower  Freeport,  and 
Upper  Freeport  coals.  It  is  now  definitely  recognized  that  the  coals  of  these 
horizons  do  not  occur  in  continuous  beds,  and  in  many  cases  not  in  exactly  the 
same  horizons;  yet  it  is  clear  that  the  corresponding  geologic  horizons  mark 
times  of  conditions  generally  favorable  for  coal  formation  and  that  no  coal 
of  wide  extent  is  found  at  other  levels.  No  one  of  them  is  continuously  workable, 
but  the  Lower  Kittanning  and  the  Upper  Freeport  coals  are  widely  workable, 
and  the  Lower  Freeport  has  a  splendid  development  over  several  counties  in 
the  northeast  part  of  the  field.  The  Brookville  or  "A"  coal  is  of  workable 
thickness  in  spots  over  a  large  part  of  the  marginal  belt  of  the  coal  measures, 
especially  in  Jefferson,  Clearfield,  Centre,  Cambria,  and  Somerset  counties. 
The  Clarion  or  "A'"  coal  reaches  workable  thickness  in  about  the  same  belt, 
though  the  two  are  seldom  of  workable  thickness  in  the  same  section.  Both  of 
these  coals  are  apt  to  be  impure  when  thick.  The  Lower  Kittanning  or  "B" 
coal  is  the  most  persistent,  uniform,  and  reliable  of  the  Allegheny  coals,  although 
it  is  thinner  than  the  Freeport  coals,  seldom  exceeding  a  thickness  of  4  feet. 
It  is  exposed  in  workable  thickness  and  purity  in  11  of  the  counties.  The 
Middle  and  the  Upper  Kittanning  horizons,  "C"  and  "C'",  contain  but 
little  workable  coal,  though  the  Upper  Kittanning  shows  cannel-coal  at  a  number 
of  points  and  stands  fourth  in  productivity.  The  Lower  Freeport  coal,  "D," 
is  finely  developed  in  Clearfield,  Jefferson,  Indiana,  and  Cambria  counties— in 
the  well-known  Moshannon  (Clearfield)  Reynoldsville-Punxsutawney,  and 
Barnesboro-Patton  basins.  The  Upper  Freeport  or  coal  "E"  is  a  variable  and 
complex  bed,  extending  in  gross  workable  thickness  over  most  of  its  area, 
although  over  a  considerable  part  of  this  territory  it  is  too  much  broken  up  and 
too  impure  for  profitable  mining.  It  appears  to  be  entirely  absent  in  some 
localities. 

As  a  whole,  the  Allegheny  formation  yields  about  40  per  cent  of  the  total 
output  of  bituminous  coal  in  the  State, 


106  STEAM-BOILER  ECONOMY. 

The  Upper  Barren  measures  contain  but  one  seam  of  commercial 
importance,  the  Washington  seam,  which  attains  its  best  development, 
3  to  3|  feet,  in  Washington  and  Fayette  counties. 

The  Upper  Productive  Coal-measures  contain  the  great  Pittsburgh 
seam,  6  to  12  feet  thick,  in  Fayette,  Washington,  Allegheny,  West- 
moreland, and  Greene  counties,  smaller  areas  also  occurring  in  In- 
diana, Somerset,  and  Beaver  counties.  The  famous  Connellsville  coke 
is  made  from  this  seam.  The  Connellsville  region  is  a  narrow  strip, 
about  3  miles  wide  and  60  miles  in  length.  The  Pittsburgh  seam  here 
affords  from  7  to  8  feet  of  coal.  The  quality  of  the  coal  is  inter- 
mediate between  the  semi-bituminous,  lying  to  the  east  of  it,  and 
the  fat  bituminous  coals,  to  the  north  and  west.  The  Waynesburg 
bed,  an  important  seam  in  Greene,  Washington,  Fayette,  and  West- 
moreland counties;  the  Uniontown,  in  Fayette  and  Greene  counties; 
the  Sewickley  and  Redstone  beds,  in  Westmoreland  and  Alleghany 
counties,  are  also  in  the  Upper  Productive  measures. 

The  Lower  Barren  measures  contain  several  workable  beds  of 
limited  area  in  Indiana,  Somerset,  Butler,  Armstrong,  and  Beaver 
counties. 

The  Lower  Productive  measures  contain  the  Freeport  Lower  coal,  a 
bed  of  great  importance  in  Jefferson,  Indiana,  Clearfield,  Cambria, 
Armstrong,  Centre,  and  Allegheny  counties,  and  workable  in  parts  of 
Beaver,  Butler,  Elk,  Blair,  Cameron,  Westmoreland,  and  Fayette 
counties;  the  Freeport  Upper  coal,  workable  in  fifteen  counties;  the 
Kittanning  Upper,  or  Darlington,  bed,  consisting  partly  of  cannel  and 
partly  of  bituminous  coal,  of  workable  thickness  in  parts  of  Butler, 
Armstrong,  Somerset,  Beaver  (cannel),  Indiana,  Jefferson,  Elk,  and 
Lycoming  counties;  the  Kittanning  Middle,  locally  workable  in  But- 


For  about  600  feet  above  the  Upper  Freeport  bed  occurs  the  Conemaugh 
formation,  or  ''Lower  Barren  Measures. "  It  contains  six  or  more  coals,  which, 
however,  are  workable  only  in  very  restricted  areas,  their  best  development 
being  found  in  the  Berlin  Basin  in  Somerset  County. 

Just  above  the  Conemaugh  formation  lies  the  Pittsburgh  coal,  the  most 
uniform  in  quality  and  thickness,  and  for  a  given  area  the  most  valuable  coal 
bed  in  the  bituminous  field  of  Pennsylvania.  Although  not  of  as  high  a  grade 
as  the  best  Allegheny  coals  to  the  east,  and  although  varying  greatly  in  quality 
from  east  to  west,  on  the  whole  the  Pittsburgh  coal,  on  account  of  its  thickness, 
its  regularity,  its  high  grade,  and  its  adaptability  for  the  production  of  coke  and 
illuminating  gas,  has  long  been  the  most  famous  bituminous  coal  bed  in  America. 
It  is  confined  to  the  southwestern  part  of  the  State.  The  bed  gives  9  feet  of 
available  coal  over  large  areas,  and  seldom  runs  under  4  feet.  Above  the  Pitts- 
burgh coal  occur  the  Redstone,  Sewickley,  Uniontown,  and  Waynesburg  coals, 
which  are  of  good  workable  thickness  locally,  but  in  the  presence  of  the  great 
Pittsburgh  coal  are  but  little  mined. 


COAL-FIELDS  OF  THE   UNITED  STATES. 


107 


ler,  Lawrence,  Jefferson,  Armstrong,  Elk,  Cameron,  and  Clarion 
counties;  the  Kittanning  Lower,  workable  in  twenty-two  counties,  an 
excellent  coking  coal  along  the  Allegheny  escarpment,  and  in  the 
western  counties  often  a  good  gas-coal ;  the  Millerstown  bed,  locally 
workable  in  Butler  county;  the  Clarion  bed,  in  some  of  the  western 
counties,  usually  quite  thin;  and  the  Brookville  bed  "A"  of  the 
Allegheny  escarpment  counties,  often  a  very  sulphurous  coal. 

The  Conglomerate  series  contains  the  Mercer  Upper  and  Lower 
coals,  workable  over  limited  areas  in  Lawrence,  Jefferson,  McKean, 
Elk,  Mercer,  and  Venango  counties;  the  Quakertown  coal,  workable 
over  a  small  area  in  Mercer  County;  and  the  Sharon  coal,  good  but 
nearly  exhausted  in  Mercer  County,  and  thin  and  inferior  in  Warren 
and  Crawford  counties. 

Exhaustion  of  Pennsylvania  Coal, — M.  R.  Campbell  (Mineral 
Resources  of  1910)  estimates  the  amount  of  anthracite  remaining 
at  16,640,000,000  tons.  If  half  of  it  is  lost  in  mining,  the  rate  of 
production  in  1910  would  exhaust  it  all  in  99  years.  The  bitumi- 
nous coal  remaining  to  be  mined  is  a  little  over  109,000,000,000  tons, 
which  at  the  rate  of  exhaustion  in  1910  would  last  480  years. 

Analyses  of  Pennsylvania  Bituminous  and  Semi-bituminous  Coals. 
— The  analyses  given  in  the  two  following  tables  are  selected  from 
reports  of  the  Pennsylvania  Geological  Survey  and  from  various  papers 


PENNSYLVANIA   SEMI-BITUMINOUS    COALS. 


0) 

*  * 

M 

County. 

s-a 

1 
| 

1 

M 

°"*H 

wl'f 

JD   S 

! 

1 

1 

^ 

III 

a>u 

£ 

£ 

< 

* 

Bradford  
Sullivan  

7 
12 

0.82 
3.24 

16.95 
13.03 

69.26 
72.74 

0.67 
0.61 

12.29 
10.38 

19.7 
15.2 

15,800 
15,700 

Tioga..  

17 
2 

1.65 
1.06 

20.50 
17.53 

67.79 
72.42 

1.26 
0.84 

8.85 
8.15 

23.2 
19.6 

15,750 
15,700 

Centre  
Huntingdon  | 

1 

Extremes  of 
5 

0.60 
/  0.47 
1  0  79 

22.60 
13.84 
17.38 

68.71 
72.85 
78.46 

2.69 
1.98 
0.88 

5.40 
8.16 
4.81 

24.7 
15.0 
18.6 

15,800 
15,700 
15,800 

Blair*  

9 

1.06 

27.27 

60.69 

2.31 

8.66 

31.0 

15,550 

Cambria: 
Lower  bed,  B  
Upper  bed,  C  

7 

1 

0.74 
1.14 

21.21 
17.18 

68.94 
i  7.3.42 

1.98 
1.41 

7.51 
6.58 

23.5 
19.0 

15,750 
15,800 

Clearfield: 
Upper  bed,  C  
Lower  bed,  D  

9 
8 
30 

0.70 
0.81 
1.15 

23.94 
21.10 
19.77 

69.28 
74.08 
67.78 

1.42 
0.42 
1.61 

4.62 
3.36 
9.67 

25.7 
22.2 
22.6 

15,700 
15,800 
15,800 

*  According  to  these  analyses  the  Blair  Co.  coals  should  not  be  included  in  the  semi- 
bituminous  class.  They  are  higher  in  volatile  matter  than  the  semi-bituminous  coals  of 
Cambria  Co.,  which  is  west  of  Blair  Co. 


108 


STEAM-BOILER  ECONOMY. 


PENNSYLVANIA   BITUMINOUS   COALS. 


M-S.2 

03 

<S      <u 

.5  §.-2 

-  • 

1 

| 

?o| 

SfcJ 

County. 

^"0. 

" 

3 

§  ?, 

S 

Is 

e  * 

1 

i 

1 

3 
ft 

a 

Ifei 

iid 

3CC 

^ 

•3 

.2 

3 

"5 

'o  ^"^ 

a*"*  ° 

£ 

& 

> 

fe 

CO 

•< 

> 

^ 

Jefferson  

26 

1.21 

32.53 

60.99 

1.00 

3.76 

34.8 

15,300 

Indiana                                          .  . 

29 

0.98 

29.26 

58.74 

1.73 

9.46 

33.3 

15,400 

Westmoreland  

27 

1.14 

32.27 

59.23 

1.50 

5.97 

35.3 

15,200 

Fayette                                      .... 

12 

0.95 

29.75 

60.47 

1.79 

7.04 

33.0 

15,400 

Potter  

3 

1.72 

32.28 

55.32 

1.01 

9.67 

36.8 

15,100 

McKean    .                                     .  . 

11 

2.25 

34.49 

46.25 

2.97 

14.02 

42.6 

14,600 

Clarion  

7 

1.97 

38.60 

54.15 

1.19 

4.10 

41.6 

14,700 

Armstrong 

1 

1.18 

42.55 

49.69 

2.00 

4.58 

46.1 

14,000 

Butler  

11 

1.91 

39.88 

48.97 

1.97 

7.22 

44.9 

14,200 

Lawrence 

14 

2.11 

40.45 

52.51 

1.37 

3.25 

43.5 

14,500 

Beaver  

20 

1.96 

39.04 

50.20 

2.00 

6.96 

43.7 

14,500 

Washington 

21 

1.16 

37.11 

50.99 

2.06 

8.72 

42.1 

14,700 

Greene  

17 

1.14 

35.74 

51.75 

1.79 

9.10 

40.8 

14,800 

Youghiogheny  River*                .  . 

1.03 

36.49 

59.05 

0.81 

2.61 

37.9 

15,100 

Connellsville  t  

1.26 

30.10 

59.61 

0.78 

8.23 

33.5 

15,400 

*  The  Youghiogheny   River  is  in  Allegheny,   Westmoreland,  and    Fayette   counties.     The 
coal  mined  along  this  river  is  a  favorite  coal  in  the  Ohio  and  Mississippi  River  markets. 

t  Connellsville  is  in  Fayette  County.     The  coal  of  this  region  is  chiefly  used  for  making 
coke  for  blast-furnace  and  foundry  purposes. 


Erie      L-r 


42.6 
Ik 


I 

i  Crawford 


j  Mercer  ( 

JV/Clarion} 

f V  "      1    41.6 

Lawrence7 

43.5  i  6utler  ! 
I j    44_9 


—  »_.  —  ...«_.•_.  WM*,*^*  MM*  ~-»*  ••—•  M»*M^»«M»««p»» 

Mc.Kean    |  Prrf1._,        Tioqa     i   Bradford    | 
4-9.fi  Potter  l  o  )9? 

I       25-2  •      •     | 

r-v-- 


\S«IUyan 


LT^TTTI  ^coming  ^W* L- 

\  y  >^\  \  i9.6      x-v-i 
'--(• 


V 


ICIearfield  ^'  \ -  / 

24.0     /     Center       /  __ 
,  /  /  24.T          ,^'r" 

/  Indiana-' -> — ^-^. 

/    33.3    /Cambria/     ^ 


jWashington 
j       4?.l 

j  Greene 
40.8 


22.6       j 


/Bedford!    ~^/  i 


FIG.  5. — SEMI-BITUMINOUS  AND  BITUMINOUS  COAL  REGION  OF  PENNSYLVANIA. 
(The  figures  under  the  names  of  the  counties  represent  the  percentage  of  vola- 
tile matter  in  the  combustible,  as  given  in  the  table  of  analyses.) 


CO  AIRFIELDS  OF  THE  UNITED  STATES. 


109 


in  the  Transactions  of  the  American  Institute  of  Mining  Engineers. 
The  figures  of  approximate  heating  value  per  Ib.  of  combustible  are 
interpolated  from  the  table  on  p.  56  showing  the  relation  of  heating 
value  to  the  percentage  of  volatile  matter  in  the  combustible.  For 
the  semi-bituminous  coals  they  are  probably  within  2  per  cent  of 
being  accurate;  for  the  bituminous  coals  within  4  per  cent. 

The  figures  of  volatile  matter  per  cent  of  combustible  are  entered 
on  the  accompanying  map  under  the  names  of  the  several  counties. 
It  will  be  seen  that  there  is  a  general  tendency  for  the  volatile  matter 
to  increase  towards  the  west  and  north.  Blair  County  seems  to  be  an 
exception.  The  boundary  line  along  which  the  semi-bituminous  coals 
grade,  more  or  less  rapidly,  into  the  bituminous,  and  the  location  of 
beds  of  bituminous  coals  within  the  limits  of  the  portion  of  the 
field  which  contains  the  semi-bituminous  coals,  as  far  as  the  author 
is  aware,  have  not  yet  been  laid  down  on  any  map. 

The  difference  between  the  semi-bituminous  and  the  bituminous 
coals  of  Pennsylvania  is  an  important  one  .economically.  The  former 
have  on  the  average  a  heating  value  per  pound  of  combustible  about 
6  per  cent  higher  than  the  latter,  and  they  also  burn  with  much  less 
smoke  in  ordinary  furnaces. 

The  following  tables  show  the  great  similarity  in  composition  in 
the  coals  of  the  upper  and  lower  coal-measures  in  the  same  geo- 
graphical belt  or  basin.  They  also  show  the  tendency  of  the  volatile 
matter  to  increase  to  the  westward: 

ANALYSES    FROM    THE    UPPER    COAL-MEASURES    (PENNA)    IN   A   WESTWARD    ORDER. 


Localities. 

Moisture. 

Vol.  Mat. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Anthracite  

1  35 

3  45 

89  06 

5  81 

0  30 

Cumberland,  Md  

0.89 

15  52 

74  28 

9  29 

0  71 

Salisbury  Pa 

1  66 

22  35 

68  77 

5  96 

1  24 

Connellsville,  Pa  
Greensburg  Pa 

1  02 

31.38 
33  50 

60.30 
61  34 

7.24 
3  28 

1.09 
0  86 

Irwin's,  Pa 

1  41 

37  66 

54  44 

5  86 

0  64 

ANALYSES    FROM    THE    LOWER   COAL-MEASURES   IN   A   WESTWARD    ORDER. 


Localities. 

Moisture. 

Vol.  Mat. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Anthracite 

1  35 

3  45 

89  06 

5  81 

0   30 

Broad  Top 

0  77 

18  18 

73  34 

6  69 

1  02 

Bennington. 

1  40 

27  23 

61  84 

6  93 

2  60 

Johnstown.       

1.18 

16  54 

74  46 

5  96 

1  86 

Blairsville      

0.92 

24.36 

62  22 

7  69 

4  92 

Armstrong  Co  

0.96 

38.20 

52.03 

5  14 

3  66 

110  STEAM-BOILER  ECONOMY. 

Maryland  Semi-bituminous  Coal. — The  Cumberland  coal-field,  in 
Allegheny  Co.,  Md.,  is  30  miles  long  and  of  an  average  breadth  of  4^ 
miles.  Its  northern  end  reaches  into  Pennsylvania  and  its  southern 
extremity  into  West  Virginia.  The  main  bed  is  from  12  to  14  ft. 
thick.  The  coal  is  one  of  the  best  steam-coals  mined  in  the  United 
States.  It  is  jet  black  and  glossy;  is  friable,  and  becomes  pulverized 
in  transportation  and  handling.  There  are  several  other  beds  from  2 
to  6  ft.  in  thickness,  the  whole  series  of  the  Pennsylvania  coal-meas- 
ures being  found  in  the  district. 

"Mineral  Resources"  of  1910  estimates  the  amount  of  coal  that 
still  remains  in  an  area  of  455  square  miles  in  Maryland  as  7,802,- 
000,000  tons,  or  over  900  times  the  exhaustion,  including  waste, 
in  1910. 

Elk  Garden  and  Upper  Potomac  Coal-fields.* 

On  the  extreme  fringe  of  the  great  Appalachian  coal-basin  is  a  long, 
narrow,  detached  coal-field,  which  is,  in  some  respects,  one  of  the  most 
important  in  the  United  States.  This  field,  about  90  miles  long  by 
2J  to  16  miles  wide,  extends  from  the  southwest  corner  of  Somerset 
County,  Pa.,  through  Allegany  and  Garrett  counties,  Md.,  Mineral, 
Grant,  and  Tucker  counties,  W.  Va.,  into  Randolph  County,  W.  Va.  In 
this  distance  four  distinct  subdistricts  are  recognized,  the  Wellersburg 
in  Pennsylvania,  and  Cumberland-Georges  Creek  in  Maryland,  and  the 
Elk  Garden  and  the  Upper  Potomac  in  West  Virginia.  It  is  the 
nearest  to  tide-water  of  all  the  bituminous  coal-fields  which  supply  the 
great  coal  markets  of  the  northern  Atlantic  seaboard,  and  its  coal-beds 
are  so  situated  as  to  permit  a  well-nigh  unlimited  increase  of -pro- 
duction should  the  trade  of  these  markets  demand  it. 

This  great  coal-field  has  sometimes  been  termed  the  Cumberland 
coal-field,  but  the  name  is  now  more  appropriately  applied  to  a  coal 
(that  of  the  Big  Vein)  which  is  not  mined  throughout  the  entire 
district.  As  the  district  is  watered  chiefly  by  the  Potomac  River  and 
its  tributaries,  and  as  most  of  the  mining  is  along  the  banks  of  that 
stream,  the  name  "Potomac  Basin"  has  been  suggested  for  this  entire 
coal-field;  the  distinctive  and  well-known  names  of  the  several  sub- 
basins,  however,  being  still  retained. 

The  general  course  of  this  basin  is  northeast  and  southwest.     It  is 

*  Abstract  from  a  paper  by  Joseph  D.  Weeks,  read  before  the  American 
Institute  of  Mining  Engineers,  1894. 


COAL-FIELDS  OF  THE  UNITED  STATES.  Ill 

hemmed  in  by  the  Alleghany  Front  Mountains  on  the  east  and  the 
Backbone  Mountains  on  the  west.  Its  general  shape  from  Pennsyl- 
vania to  near  the  southern  border  of  Tucker  County,  W.  Va.,  is  that  of 
a  wedge,  very  narrow  in  Pennsylvania,  only  2J  miles  wide  at  the  State 
line,  and  widening  as  the  mountains  draw  away  from  each  other,  until 
at  the  point  named  in  Tucker  County,  it  is  some  16  miles  wide. 

The  northern  end  of  this  field  passes  through  the  western  part  of 
Alleghany  County  and  a  portion  of  the  eastern  part  of  Garrett  County, 
Maryland,  and  from  it  the  entire  coal  product  of  Maryland  is 
obtained. 

Virginia. — There  are  several  detached  coal-fields  in  the  Mesozoic 
rocks  east  of  the  Alleghany  Mountains.  They  are  described  by  0.  J. 
Heinrich,  in  Trans.  A.  I.  M.  E.,  1878,  vol.  vi.  The  Eichmond  basin, 
189  square  miles,  chiefly  in  Powhatan  and  Chesterfield  counties,  west 
.of  Richmond,  is  the  most  important.  It  contains  two  workable  beds, 
the  lower  3  to  5  ft.  thick,  and  the  upper  20  to  40  ft.  thick.  The  coal  is 
chiefly  bituminous,  containing  30  per  cent  or  upwards  of  volatile 
matter  in  the  combustible,  but  at  Carbon  Hill  semi-bituminous  is 
found,  also  "carbonite"  or  natural  coke,  corresponding  in  analysis  to 
semi-anthracite. 

Semi-anthracite  coal,  with  about  84  to  86  per  cent  fixed  carbon 
in  the  combustible,  is  mined  in  Pulaski  and  Montgomery  counties. 

The  Appalachian  semi-bituminous  coals  are  found  in  the  south- 
western portion  of  the  State,  in  .Tazewell  County,  on  the  West 
Virginia  border,  and  the  bituminous  coals  in  the  southwestern  corner 
of  the  State  near  the  Kentucky  line. 

The  Pocahontas  coal-field  embraces  parts  of  Buchanan,  Dickin- 
son, Lee,  Russell,  Scott,  Tazewell,  and  Wise  counties,  at  the  southern 
edge  of  the  Flat  Top  region,  including  the  Clinch  valley  field,  con- 
taining the  Lower  Productive  measures  of  the  Appalachian  field. 

The  Pocahontas  Flat  Top  coal-measures  are  above  the  water-level, 
in  seams  ranging  from  5  to  13  ft.  in  thickness,  extending  through  an 
area  estimated  to  contain  not  less  than  300  sq.  miles.  Pocahontas 
semi-bituminous  coal  is  from  the  Lower  coal-measures  and  contains 
from  18  to  20  per  cent  of  volatile  matter.  It  is  mined  in  Tazewell, 
Wise  and  Lee  counties,  Va.,  and  in  Mercer  and  McDowell  counties, 
W.  Va.,  the  adjoining  counties  to  the  north.  The  veins  dip  to  the 
north  and  west,  and  the  extension  of  the  Ohio  division  of  the  Nor- 
folk and  Western  Railroad  north  to  the  Ohio  River  and  the  road 
west  to  the  Cumberland  Mountains  pass  through  the  Middle  and 


112 


STEAM-BOILER  ECONOMY. 


Upper  measures,  thus  opening  up  coal  of  greater  volatile   matter, 
bituminous,  splint  and  cannel. 

The  development  of  this  now  famous  region  began  in  1881,  but  not 
until  1888  was  any  coal  shipped  out  of  the  country.  In  1893  the 
Pocahontas  field  was  open  in  Wise  County,  Virginia,  and  1905  in  Lee 
County,  and  development  work  has  been  done  in  Dickinson,  Eussell 
and  Buchanan  counties.  In  1910  the  production  of  Wise  County 
was  three  times  that  of  Tazewell  County. 

North  Carolina. — Semi-anthracite  is  found  in  two  unimportant 
beds,  18  inches  thick,  in  the  Dan  Eiver  field,  40  miles  long,  4  to  7 
miles  wide,  of  which  8  miles  are  in  Virginia.  The  Deep  River  field, 
30  miles  long  by  3  wide,  contain  five  beds,  all  differing  in  character, 
ranging  from  bituminous  coal  to  an  impure  plumbago,  as  shown  by 
the  following  analyses : 


Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Bituminous,  3  ft.  thick  
Semi-bituminous,  1  ft.  thick            

32.8 

23.6 

63.8 
72.6 

4 
4 

Anthracite,  3  ft.  thick.                

6.6 

83.8 

9.6 

Plumbaginous  slate,  2  ft.  thick.        

10.4 

78 

Plumbago,  4  ft.  thick      .                            ... 

18.2 

74 

The  Cummock  or  Egypt  mines  in  the  Deep  River  field  were 
operated  from  1889  to  1905,  producing  23,000  short  tons  in  1902, 
17,300  tons  in  1903,  7000  tons  in  1904,  and  1557  tons  in  1905. 
No  coal  has  been  produced  in  the  State  since  1905. 

West  Virginia. — Out  of  54  counties  only  6  are  destitute  of  coal. 
The  quality  is  semi-bituminous  in  the*  eastern  portion  of  the  coal-bear- 
ing district  and  bituminous  in  the  western.  The  first  coal-field  is  the 
Potomac  basin,  an  extension  of  the  Cumberland  semi-bituminous  coal- 
field of  Maryland.  The  Monongahela  basin  embraces  five  beds,  of 
which  the  Pktsburg,  9^  ft.  of  clear  coal,  is  the  most  important.  This 
is  a  gas-coal,  and  makes  a  hard  coke,  but  is  high  in  sulphur.  The  New 
River  coal-field  lies  in  Fayette  and  Raleigh  counties,  bordering  the 
New  River  from  40  miles  from  Quinnimont  to  Kanawha  Falls.  It 
contains  both  semi-bituminous  and  bituminous  steam,  coking  and  gas- 
coals  of  excellent  quality.  The  Kanawha  coal-field  lies  along  the  Kan- 
awha River  and  its  branches,  below  the  junction  of  the  New  and  Gauley 
rivers.  The  coal  is  bituminous,  and  includes  gas-coals,  cannel  and 


COAL-FIELDS  OF   THE   UNITED  STATES. 


113 


hard  splint  coal.  It  is  largely  mined  for  shipment  down  the  Ohio 
Kiver.  The  Pocahontas  field  lies  in  the  southwestern  corner  of  the 
State,  in  McDowell  and  Mercer  counties,  and  extends  across  the 
State  line  into  Virginia.  All  of  the  Pocahontas  coal  is  a  high-grade 
semi-bituminous.  As  a  steam  coal  it  ranks  with  the  best  Cumberland, 
Md.,  and  Clearfield,  Pa.,  coals,  and  as  a  coke  producer  it  rivals 
the  Connellsville,  Pa.,  coal. 

The  amount  of  coal  remaining  in  West  Virginia  in  1910  is 
estimated  at  about  149,000,000,000  tons,  and  at  the  rate  of  production 
in  1910,  adding  50  per  cent  for  loss  it  would  last  for  about  160 
years. 

WEST  VIRGINIA   ANALYSES,    FROM   PRIME'S  REPORT  OF  THE   CENTENNIAL  EXHIBIT. 


Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Sul- 
phur. 

Ash. 

Piedmont   ]Mineral  Co 

0   82 

19   36 

75  86 

0*71 

3  96 

Austen  Preston  Co 

0  11 

31    12 

66  29 

0  64 

2  48 

Kingwood  top  of  bed 

0  34 

31  47 

65  66 

0  58 

2  53 

Monongahela  Co.,  Upper  Freeport  bed 
'  '    Pittsburg  bed  
'  '    Redstone  seam  .... 
'  '    Sewickley  seam.  .  .  . 
'  '    Waynesburg  seam.  . 
Despard   Harrison  Co 

0.63 
0.39 
0.37 
0.44 
0.74 

28.06 
38.64 
37.88 
35.78 
35.36 
40  00 

54.28 
54.77 
54.36 
54.31 
56.35 
53  30 

0.77 
2.54 
2.87 
3.10 
0.71 

17.03 
6.20 
7.39 
9.47 
7.55 
6  70 

Murphy  s  Run  Harrison  Co     

1  58 

37  10 

49  08 

2  84 

9  40 

Wood's  Run  Ohio  Co  

1  74 

42  97 

50  99 

2  88 

4  30 

Hartford  Putnam  Co  

3.43 

44.38 

46.88 

1.57 

5  30 

Osborn.  Wavne  Co  .  . 

2.30 

40.43 

48.72 

0.76 

8.55 

CANNEL   COAL. 


P6yton£i  BoonG  Co 

46  00 

41  00 

13  00 

ANALYSES    OF   WEST   VIRGINIA_COALS,    NEW   RIVER    REGION. 


Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Sul- 
phur. 

Ash. 

Ouinnimont  lump      

0.76 

18.65 

79.26 

0.23 

1.11 

'  '           slack                              .... 

0.83 

17.57 

79.40 

0.28 

1.92 

Fire  Creek                                  

0.61 

22.34 

75.02 

0.56 

1.47 

Londale  (Sewell)                   

1.03 

21.38 

72.32 

0.27 

5.27 

Nuttalburg                     

1.35 

25.35 

70.67 

0.57 

2.10 

Hawk's  Nest                                  

0.93 

21.83 

75.37 

0.26 

1.87 

1.40 

32.61 

63.10 

0.74 

2.15 

114 


STEAM-BOILER  ECONOMY. 


Eastern  Kentucky, — The  Appalachian  field  extends  into  Eastern 
Kentucky,  including  fifteen  counties  and  portions  of  five  others,  cover- 
ing altogether  10,270  square  miles.  The  following  analyses  are  from 
Owen's  Geological  Survey  of  the  State: 


No. 

of 
Bed. 

Locality. 

Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sul- 
phur. 

1 

Lawrence  County. 

3  50 

36  30 

57  30 

2  90 

1  15 

2 

Carter  County  

4  10 

34  60 

55  25 

4  77 

1  41 

3 

Greenup  County. 

3  56 

35  00 

52  34 

9  02 

2  59 

4 

Carter  County  (cannel). 

0  60 

66  30 

28  30 

4  80 

1  32 

5 

Lawrence  County. 

3  20 

32  30 

53  00 

11  50 

1  20 

fi 

Boyd  County. 

3  27 

33  77 

54  51 

8  91 

1  56 

7 

Coalton  County 

5  19 

32  04 

55  59 

6  71 

1  68 

The  following  analyses  of  Eastern  Kentucky  coals  are  taken 
from  a  report  by  Capt.  H.  S.  Hodges,  Corps  of  Engineers,  IT.  S.  A., 
January,  1900,*  on  a  Survey  of  the  Big  Sandy  Eiver,  West  Virginia 
and  Kentucky,  including  Levisa  and  Tug  Forks : 


No.  of 
of  Anal- 
yses. 

Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sul- 
phur. 

Vol.  Mat. 
%of 
Com- 
bustible. 

LAWRENCE  COUNTY: 

Peach  Orchard  coal 

2 

4.60 

35.70 

53.28 

6.42 

1.08 

40.1 

McHenry  coal  .... 

1 

(3.24 
\3.36 

36.56 
37.05 

54.95 

52.82 

5.24 
5.55 

1.19 

1.22 

40.0 

41.2 

JOHNSON  COUNTY: 
Bituminous  coals  .  . 

5 

2.66 
.20 

38.04 
41.80 

56.30 
46.00 

3.00 
11.00 

1.29 
0.96 

40.3 
47.6 

Cannel  coals 

8 

.80 

49.20 

44  .  00 

5.00 

0.85 

52.8 

.20 

64.39 

26.36 

8.05 

1.67 

71.0 

FLOYD  COUNTY: 

Q 

.80 

33.80 

60.60 

1.80 

0.48 

35.8 

V 

.30 

36.70 

51.70 

10.30 

1.36 

41.5 

PILE  COUNTY: 

07 

.80 

26.80 

67.60 

3.80 

0.97 

28.4 

o< 

.60 

41.00 

50.37 

7.00 

0.03 

42.9 

Average  of 

37 

34.77 

58  61 

37.2 

Cannel  coal 

1 

0  58 

54  07 

40  64 

4  70 

0.87 

57.1 

MARTIN  COUNTY: 

fl.46 

32,60 

62.68 

3.26 

34~2 

\2.47 

34.18 

55.03 

8.32 

1.17 

38.3 

The  analyses  here  given  are  selected  from  those  in  the  original 
report,  to  show  the  range  of  quality,  as  indicated  by  the  percentage  of 


*  H.  R.  Document  No.  326,  56th  Congress,  1st  Session. 


COAL-FIELDS   OF    THE    UNITED   STATES, 


115 


volatile    matter    in    the   combustible,    of   the    coals   of   the    several 
counties. 

The  relative  location  of  the  counties,  and  the  percentage  of  vola- 
tile matter  per  pound  of  combustible  in  the  bituminous  (not  cannel) 
coal  in  each  county,  as  given  in  the  table,  are  shown  in  the  accom- 
panying map. 


\          <.T.s~  ~'\~~ <rr~        -t/ 
\Fl£yd  1 

•<38'V)  ™'  /  v 

\Knon  "\      /    .  /Bgehana^ 


FIG.  6. — BIG  SANDY  COAL  REGION  OF  EASTERN  KENTUCKY. 


The  author  commends  to  State  geologists  and  others  who  have 
occasion  to  make  reports  on  the  extent  and  quality  of  coal  deposits 
the  method  of  mapping  both  the  location  and  the  quality  which  is 
shown  here  and  also  on  page  109.  The  reports  of  the  U.  S.  Geologi- 
cal Survey,  of  the  U.  S.  Census,  and  of  the  Geological  Surveys  of 
the  several  States  would  be  of  greater  value  than  they  now  are  if 
they  contained  such  maps. 

The  eastern  Kentucky  coals  are  mostly  high-grade  gas  or  coking 
coals,  with  some  cannel  coal.  For  lack  of  transportation  the  produc- 
tion has  been  small.  In  1910  out  of  14,623,319  short  tons  mined 
in  the  State,  6,279,024  tons  are  credited  to  eastern  Kentucky. 


116 


STEAM-BOILER  ECONOMY. 

ANALYSES  OF  KENTUCKY  COAL. 


Moist- 

Volatile 

Fixed 

Ash 

Volatile 
Matter 
Per  cent 

B.T.U. 

per  Lb. 

ure. 

Matter. 

Carbon. 

of 
Com- 
bustible 

Dry  Coal 

Com- 
bustible. 

Bell  

2.07 

35.03 

58.69 

4.21 

0.95 

37  4 

14,852 

15  520 

Harlan  

2.88 

35.64 

56.90 

4.58 

0.78 

38.5 

14,692 

15419 

Hopkins  
Johnson  
Letcher  
Muhlenburg.  .  . 
Ohio  

8.19 
4.46 
2.40 

8.75 
9.32 

40.03 
39.99 
35.84 
38.18 
41  .  37 

43.09 
51.00 
58.29 
43.81 
40.06 

8.69 
4.55 
3.47 
9.26 
9.25 

3.62 
1.01 
0.73 
4.01 
2.95 

48.2 
44.0 
38.1 
46.6 
50.8 

13,375 
13,988 

13,233 
13,308 

14,473 
14,687 

14,728 
14,820 

Pike  

2.34 

31.42 

61.43 

4.81 

0.64 

33.9 

14,219 

14,956 

Union  

7.00 

32.87 

54.02 

6.11 

1.15 

37.9 

14,482 

15,500 

Webster  

5.23 

37.24 

50.09 

7.44 

3.35 

42.6 

14,142 

15,318 

Whitley 

2  40 

39  01 

53  24 

5  35 

1  54 

42  3 

14,023 

14836 

Martin  

3.10 

31.78 

54.74 

10.38 

'0.88 

36.7 

Morgan  

42.03 

8.65 

1.10 

Floyd 

2  41 

34  70 

57  65 

5  24 

0.66 

37.6 

Menifee  

4.18 

35.78 

54.80 

5.24 

0.94 

39.5 

Magoffin  

2.94 

37.57 

53.46 

6.03 

0.90 

41.3 

Wolf  
Pulaski  
Rock  Castle.  .  . 
Laurel 

3.62 
2.22 
3.52 
2  38 

35.36 
35.27 
33.77 
35.30 

54.67 
54.87 
54.99 
58.46 

6.35 
7.64 

7.72 
3.86 

1.83 
1.85 
1.77 
1.12 

39.3 
39.1 
37.1 
37.6 

Breathitt  
Perry 

3.95 

37.63 
38.04 

50.57 

7.85 
5.54 

1.24 
0.82 

42.7 

Lawrence. 

4.24 

38.04 

49.49 

8.23 

1.44 

43.5 

Leslie 

36.91 

6.62 

0.57 

Knox  
Jackson  

1.50 
2.70 

34.54 
37.11 

59.16 
52.31 

4.80 

7.88 

0.93 
1.11 

36.9 
41.5 

NOTE. — The  above  analyses  are  from  reports  of  U.  S.  Geological  Survey,  Kentucky  Geolog- 
cal  Survey  and  private  reports.     Contributed  by  Mr.  Howard  N.  Eavenson,  Gary,  W.Va.,  1914. 


Western  Kentucky. — The  great  central  coal-field  extends  south 
of  the  Ohio  river  into  the  western  part  of  Kentucky.  It  underlies 
the  whole  or  portions  of  eight  counties.  It  is  mined  chiefly  in  Hop- 
kins, Muhlenberg,  Ohio,  and  Webster  counties.  (See  page  121.) 

Tennessee. — The  Appalachian  field  crosses  the  eastern  part  of 
Tennessee  in  a  comparatively  narrow  belt,  71  miles  wide  at  the  north- 
ern boundary  and  narrowing  to  50  miles  at  the  southern  or  Alabama 
and  Georgia  State  line.  The  workable  coal-area  is  confined  to 
what  is  known  as  the  Cumberland  table-land.  About  4400  square 
miles  are  contained  in  the  area,  which  is  embraced  in  nineteen  coun- 
ties. There  are  nine  seams,  of  which  six  are  over  3  feet  in  thickness. 
The  coals  range  from  semi-bituminous  to  bituminous,  and  some  are  of 


COAL-FIELDS  OF   THE   UNITED  STATES. 


117 


excellent  quality.  In  Campbell  County  is  a  part  of  the  famous  Jellico 
steam-coal  field.  The  Sewanee  vein  is  one  of  the  most  important  ones 
in  the  State  and  is  worked  extensively  in  Grundy  County.  Coke  of 
high  grade  is  made  from  the  coal  of  this  seam.  A  comprehensive 
paper  on  the  Tennessee  coal-fields,  by  Prof.  J.  M.  Safford,  was  pub- 
lished in  "Mineral  Resources/7  1892. 


ANALYSES    OF   TENNESSEE    COALS. 


Moisture  and 
Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Addison's  Creek,  Cumberland  Mountains. 
Crow  Creek 

9.00      ' 
14  00 

83.22 
77  70 

7.78 
8  30 

Sewanee  Mining  Co.                

14  21 

79  56 

6  25 

Tracy  City      

29  00 

65  50 

5  50 

Marion,  Upper  Seam  

38  00 

59  50 

2  50 

Etna  
Chattanooga  

21.39 
26.80 

74.20 
63  90 

4.41 
9  30 

Coal  Creek,  Anderson  

40.00 

55.00 

5  00 

Georgia. — The  Appalachian  coal-field  enters  the  extreme  northwest 
corner  of  the  State,  the  coal-measures  occupying  an  area  of  from  150 
to  170  sq.  miles.  The  coal  is  similar  in  quality  to  that  of  Tennessee. 
One  analysis,  from  Bade  Co.,  gave:  Moisture,  1.20;  volatile  matter, 
23.05;  fixed  carbon,  60.50;  ash,  15.16;  sulphur,  0.84.  The  coal  pro- 
duction of  Georgia  decreased  from  the  maximum  figure  of  416,951 
short  tons  in  1903  to  177,245  tons  in  1910.  The  decrease  is  attributed 
to  scarcity  of  labor. 

Alabama. — The  southern  extremity  of  the  Appalachian  coal-field 
covers  about  6000  sq.  miles,  in  the  northern  part  of  the  State.  There 
are  three  separate  basins :  the  Warrior,  5000  sq.  miles,  extending  nearly 
across  the  State ;  the  Cahaba,  nearly  400  sq.  miles,  to  the  southwest  of 
the  Warrior  field,  and  the  Coosa,  350  sq.  miles,  east  of  the  Cahaba  and 
on  the  northwest  side  of  the  Coosa  River.  The  coal-measures  contain 
ten  or  twelve  beds  of  workable  thickness.  The  Cahaba  Basin  coals  are 
the  best  in  the  State.  The  larger  bed  is  12  ft.  thick,  of  good  coal. 
Besides  these  three  basins  there  is  the  Plateau  field,  east  of  the  Warrior 
basin,  whose  resources  are  comparatively  small. 

The  following  analyses  are  from  the  reports  of  E.  A.  Smith,  State 
geologist : 


118 


STEAM-BOILER  ECONOMY. 


ALABAMA    COALS. 


Bed.                           County. 

Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sul- 
phur. 

Cahaba  Basin: 
Cahaba  Shelby    

1  66 

33  28 

63  04 

2  02 

53 

McGinnis 

1  91 

32  65 

63  91 

1  53 

63 

Moyle 

1  93 

32  84 

59  64 

5  59 

3  78 

Little  Pittshurg  
Conglomerate  
Helena. 

2.05 
2.13 
2  54 

33.47 
30.86 
29  44 

62.20 
64.54 
66  81 

2.28 
2.47 
1  21 

.64 
1.48 
53 

Montevallo 

2  13 

27  03 

66  22 

4  62 

50 

Warrior  Basin: 
Townley  Walker  
Jagger  " 

3.01 
3  09 

29.08 
29  04 

63.35 
56  54 

4.56 
11  33 

.71 
57 

Burnett's.  .    .       Marion 

3  69 

35  38 

58  52 

2  41 

1  73 

Pratt  Co.'s  ....   Upper  Jefferson 

1  47 

32  29 

59  50 

6  73 

1  22 

'  '         ...   Lower        '  ' 

1  53 

30  68 

63  69 

4  10 

61 

Ohio. — The  Appalachian  coal-field  in  Ohio  covers  more  than 
12,000  square  miles  in  the  eastern  and  southeastern  portions  of  the 
State,  its  length  being  about  180  miles  and  its  width  about  80  miles. 
The  coals  are  all  of  the  bituminous  variety,  are  known  in  general 
terms  as  block  coal,  gas-coal,  cannel-coal,  etc.,  and  by  many  special 
names,  as  Mahoning  Valley,  Hocking  Valley,  Salineville,  etc.,  accord- 
ing to  the  producing  localities.  Thirteen  workable  beds  are  found  along 
the  Ohio  Eiver,  but  only  two  of  them,  No.  6,  or  the  "Great  Vein"  of 
Perry  Co.,  and  No.  8,  or  the  Pittsburg  bed,  are  found  workable  over 
great  areas.  No.  1,  the  "block  coal"  of  the  Mahoning  Valley,  called 
elsewhere  "Massillon  "  and  "Jackson  "  coal,  is  of  great  excellence  wher- 
ever found.  It  is  thinly  laminated,  and  is  broken  by  transverse  cleav- 
ages into  cubical  blocks,  whence  its  name  of  "block  coal." 

ANALYSES  OF  OHIO    COALS  FROM    DIFFERENT  BEDS   (NEWBERRY). 


Coal, 
:    No. 

Locality. 

Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

I. 

Mahoning  Co  

2.47 

31.83 

64.25 

1.45 

0  56 

II. 

Holmes  Co        

2.15 

28.65 

52.70 

16.50 

2  13 

III. 

a 

3.90 

40.50 

49.95 

5.65 

1  55 

III. 

IV. 
IV. 

Yellow  Creek  
Coshocton  Co.  (Cannel) 
Stark  Co   

2.50 
1.50 
7.00 

36.60 
44.40 
30.80 

56.30 
44.50 
59.50 

4.60 
9.60 
2.70 

2.05 
1.72 
0  65 

V. 

Columbiana  Co    

1.15 

40.45 

53.75 

4.65 

3.51 

VI. 

(  ( 

1.60 

29.29 

64.50 

4.00 

2.80 

VI. 

Muskingum  Co  

3.47 

37.88 

53.30 

5.35 

2.24 

VI. 

Jefferson  Co 

1  40 

30  90 

65.90 

1  80 

0  98 

VII. 
VII. 

Saline  Co  
Carroll  Co 

1.70 
2.80 

34.30 
30  20 

59.50 
64.10 

4.50 
2.90 

1.63 
1  23 

VIII. 

Harrison  Co 

2.44 

32.36 

59.92 

5.28 

2  62 

COAL-FIELDS  OF   THE  UNITED  STATES. 


119 


"Mineral  Resources/'  1910,  names  the  following  as  the  important 
productive  coal  beds :  No.  1,  Block,  or  Sharon  Coal ;  No.  2,  Wellston ; 
No.  5,  Lower  Kittaning ;  No.  6,  Middle  Kittaning ;  No.  7,  Upper  Free- 
port;  No.  8,  Pittsburgh;  Pomeroy;  Meigs  Creek.  The  Hocking 
Valley  Coal  of  No.  6  bed  mined  in  Perry,  Athens  and  Hocking  counties 
is  celebrated  as  a  free-burning  coal  for  steam  and  domestic  purposes. 

The  following  are  average  figures  for  some  Ohio  coals  by  Lord  and 
Haas.  See  Chapter  V,  on  "Heating  Value  of  Coal." 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Upper  Freeport  Bed 

1  93 

37.35 

51  63 

9  10 

2  89 

Middle     Kittanning     Bed 

(Hocking  Valley)  

6.59 

35.77 

49.64 

8.00 

1.59 

Jackson  Co  

8.17 

35.79 

52.78 

3.25 

1.13 

The  following  table  of  analyses  and  heating  values  of  Ohio  coals 
has  been  contributed  by  Mr.  Howard  N.  Eavenson.     (1914.) 


ANALYSES   OF    OHIO    COAL. 


County. 

Seam.* 

Moist- 
ure. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sul- 
phur. 

B.T.U.  per  Pound. 

Coal. 

Com- 
bustible. 

Washington  

a 
b 
c 
c,d 
b,e 
e 
d,  e 
c,  e 
d,f,g 
a,  d 
a 
a,  d 
a,d 
f 
b,  c 
e,  g 
c,  e 
b,  c,  e,  g 

e 
e 
e 
d,e 
d 

3.17 
6.80 
5.23 
4.06 
4.82 
7.09 
6.37 
6.57 
7.07 
4.78 
3.50 
3.90 
4.78 
6.51 
5.60 
5.04 
4.99 
7.39 
7.31 
5.82 
3.60 
3.76 
4.22 
6.24 

37.71 
37.92 
36.86 
35.68 
39.98 
35.76 
35.57 
36.95 
34.86 
38.51 
37.52 
35.93 
35.71 
35.04 
38.34 
39.15 
39.96 
34.66 
34.92 
38.78 
36.16 
39.11 
39.80 
38.32 

47.88 
45.94 
53.19 
51.90 
45.52 
51.01 
49.80 
48.70 
47.07 
46.46 
47.34 
49.74 
51.09 
48.05 
46.11 
48.82 
46.39 
47.11 
53.56 
47.90 
55.64 
50.34 
49.24 
53.99 

11.23 
9.34 
4.72 
8.36 
9.68 
6.13 
8.25 
7.77 
11.19 
10.24 
11.63 
10.27 
8.42 
10.40 
9.94 
7.00 
8.66 
10.83 
4.21 
7.45 
4.60 
6.79 
7.24 
8.42 

5.29 
3.45 

2.17 
3.08 
3.95 
1.72 
2.31 
2.85 
3.58 
4.62 
5.58 
3.83 
2.59 
2.46 
4.30 
4.01 
4.62 
2.85 
1.00 
3.87 
1.76 
3.06 
3.94 
3.34 

12,497 
11,839 
13,504 
12,960 
12,364 
12,523 
12,267 
12,305 
11,608 
12,085 
12,325 
12,539 
12,661 
11,948 
12,092 
12,638 
12,429 
11,727 
12,514 
11,864 
14,020 
13,028 
12,825 
13,716 

14,601 
14,118 
14,997 
14,798 
14,461 
14,548 
14,369 
14,367 
14,168 
14,223 
14,355 
14,636 
14,586 
14,380 
14,319 
14,298 
14,394 
14,341 
14,143 
13,847 
15,272 
14,566 
14,404 
14,859 

Scioto           

Jefferson  

Vinton  
Hocking  
Athens  

Gallia 

Morgan                .  .  . 

Noble  

Belmont  

Meigs  
Jackson                .    . 

Muskingum  

Holmes  
Stark  .                .... 

Carroll  
Tuscarawas  
Guernsey  

*  Names  of  Seams:  a,  Meig's  Creek,  b,  Clarion,  c,  Lower  Kittaning.  d,  Pittsburgh. 
e,  Middle  Kittaning.  /,  Pomeroy.  g,  Upper  Freeport.  The  percentage  of  volatile  matter 
in  the  combustible  ranges  from  39.4  (Columbiana  Co.)  to  46.3  (Muskingum  Co.). 

THE  NORTHERN  OR  MICHIGAN  COAL-FIELD. 

The  coal  deposits  of  Michigan  are  detached  from  those  of  any 
other  State,  and  form  what  is  known  as  the  Northern  field.   The  area 


120 


STEAM-BOILER  ECONOMY. 


is  about  6700  square  miles,  the  central  point  being  near  the  town  of 
St.  Louis,  in  Gratiot  County,  and  the  southern  boundary  passing  a 
few  miles  south  of  Jackson,  in  Jackson  County.  Beyond  this  to  the 
south  there  are  several  detached  patches  of  productive  coal-measures. 
The  greatest  thickness  of  the  measures  is  found  along  a  line  extend- 
ing from  Ionia  County  to  Saginaw,  the  thickest  coal-beds  lying  along 
Six  Mile  Creek.  There  is  one  seam  of  bituminous  coal,  3  or  4  ft. 
thick,  and  toward  the  centre  of  the  basin  there  are  several  other  beds. 
One  analysis  gives :  Moisture,  2 ;  volatile  matter,  49 ;  fixed  carbon,  45 ; 
ash,  2;  sulphur,  2.  The  principal  operations  are  carried  on  near  the 
city  of  Jackson,  in  Jackson  County,  but  these  are  small  when  com- 
pared with  other  States. 

The  Michigan  coals  are  of  inferior  quality  when  compared  to  those 
shipped  by  lake  and  rail  into  the  State,  and  the  imported  coals  were 
sold  so  cheaply  until  about  1897,  that  the  development  of  the  Michigan 
field  was  insignificant.  In  that  year  the  production  reached  223,592 
tons.  The  annual  production  then  rapidly  increased.  In  1907  it  was 
2,035,858  tons,  and  in  1910,  1,534,967  tons.  The  quantity  of  coal  in 
the  State  is  estimated  at  about  12,000,000,000  tons. 

THE  ILLINOIS  COAL-BASIN. 
(Indiana,  Illinois,  and  Western  Kentucky.) 

Indiana. — The  Illinois  coal-field  extends  into  the  western  part  of 
Indiana,  covering  an  area  of  6500  square  miles,  distributed  through 
26  counties,  in  18  of  which  coal  is  produced  on  a  commercial  scale. 
The  coal  supply  of  the  State  is  estimated  at  nearly  44,000,000,000 
tons,  or  enough  at  the  rate  of  production  in  1910,  allowing  a  loss  of 
35  per  cent,  to  last  about  1800  years.  The  following  analyses  are 
given  by  the  State  Geological  Survey: 

ANALYSES    OF   INDIANA    COALS. 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Caking  Coals. 
Parke  Co 

4  50 

45  50 

45  50 

4  50 

Sullivan  Co.  coal  M  

2.35 

45.25 

51.60 

0.80 

Clay  Co 

7  00 

39  70 

47  30 

6  00 

Spencer  Co    coal  L 

3  50 

45  00 

46  00 

2  50 

Block  coals. 
Clay  Co          

8.50 

31.00 

57.50 

3.00 

Martin  Co  

2.50 

44.75 

51.25 

1.50 

Daviess  Co   

5.50 

36.00 

53.50 

5.00 

COAL-FIELDS   OF   THE   UNITED  STATES. 


121 


The  following  ultimate  and  proximate  analyses,  credited  to  Noyes, 
McTaggart,  and  Craven,  are  taken  from  Poole's  "Calorific  Power  of 

Fuels" : 


Locality. 

Carbon. 

Hydro- 
gen. 

Oxy- 
gen. 

Nitro- 
gen. 

Sul- 
phur. 

Water. 

Ash. 

Fixed 
Carb. 

Vol. 
Mat- 

Brazil  

70.50 

4.76 

16.29 

1.36 

1.39 

8.98 

6.28 

50.30 

34.49 

Lancaster  

71.41 

5.56 

18.42 

1.54 

0.62 

12.66 

2.68 

47.22 

37.64 

New  Pittsburg. 

62.88 

5.07 

13.06 

1.01 

7.46 

6.83 

13.30 

39.93 

39.92 

«           n 

65.26 

5.17 

13.25 

1.17 

5.88 

5.89 

11.48 

40.40 

42.23 

Shelburn  

66.86 

5.30 

15.69 

1.50 

2.57 

8.63 

9.05 

43.45 

38.82 

All  of  the  Indiana  coal  is  classed  as  bituminous.  That  along  the 
eastern  edge  of  the  field  is  known  as  block  or  semi-block  coal,  breaking 
through  cleavage  planes  into  rectangular  blocks.  It  is  very  pure,  dry, 
and  non-coking.  The  rest  of  the  coal  is  called  gas  or  coking  coal. 

Western  Kentucky. — The  Illinois  coal-field  extends  into  the  north- 
western portion  of  the  State,  including  ten  counties  and  portions  of 
five  others,  having  an  area  of  3888  square  miles  of  coal-measures. 
There  are,  in  places,  twelve  beds,  but  the  number  varies  with  the 
locality.  The  following  analyses  are  from  Prime's  Centennial  Report 
on  Coal : 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Coal  A  (average)  

4.15 

33.14 

55.71 

7.00 

1  87 

B  (average)  

3.65 

38.40 

51.87 

6.06 

3.12 

C  (gas-coal  laver). 

4  60 

40  10 

51  35 

3  95 

1  49 

D  (average). 

3  82 

35  31 

52  11 

8  41 

3  33 

J    (Christian  Co.)  
L  (average)  
Breckenridge  cannel  

3.70 
4.23 
1.44 

32.56 
33.21 
62.40 

50.04 
54.19 
28.20 

13.70 
8.35 
7.96 

3.72 
1.50 
2.44 

The  following  are  from  the  Geological  Survey  of  Kentucky,  1884, 
Western  Coal-Field,  D. : 


No.  of 
Samples. 

Moisture. 

Volatile 

Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Nolin  River  District 

3      { 

3.40 

to  4.  70 

30.66 
to  33.  24 

51.70 
to  54.  94 

11.06 
to  11.  70 

1.95 
to  2.  54 

Muhlenberg  Co  .... 

7      { 

3.60 
to  7.  06 

30.60 
to  38.  70 

50.50 
to  58.  80 

3.40 
to  9.  20 

0.79 
to  4.  57 

Hancock  Co  

7      { 

3.30 

33.14 

45.56 

4.20 

1.32 

I 

to  7  .  46 

to  43  .  40 

to  55  .  20 

.to  11.00 

to  4  .  04 

Ohio  Co  

»      1 

3.70 
to  5.  30 

30.70 
to  45.  70 

45.00 
to  55.  30 

3.16 
to  14.  20 

1.24 
to  3.  13 

Breckenridge  Cannel 

4      { 

0.64 
to  1.44 

54.40 
to  62.  40 

27.00 
to  32.  00 

7.96 
to  12.  30 

"i:» 

122  STEAM-BOILER  ECONOMY. 

The  Nolin  River  district  embraces  portions  of  Grayson,  Edmon- 
son,  Hart,  and  Butler  counties. 

Illinois. — The  coal-field  of  Illinois  occupies  an  area  of  35,600 
square  miles,  or  nearly  two-thirds  of  the  area  of  the  State.  The  coal- 
measures  contain  six  beds  of  workable  size,  with  a  total  thickness  of 
24  ft.,  but  the  beds  are  irregular,  often  wanting,  and  often  contain- 
ing an  inferior  quality  of  coal.  In  the  DuQuoin  district,  Perry  Co., 
two  seams,  V  and  VI,  6  to  7  ft.  thick,  are  worked  within  75  ft.  of  the 
surface.  In  the  Big  Muddy  district,  Jackson  Co.,  the  coal  occurs  near 
the  surface.  The  lower  seams  produce  a  good  block  coal.  From  the 
Belleville  district,  St.  Clair  Co.,  St.  Louis  obtains  most  of  its  bitumin- 
ous coal.  Coal  seam  VI,  5  to  7  ft.  thick,  is  principally  worked.  The 
lower  seams  contain  more  sulphur  and  the  quality  varies.  Other  large 
producing  districts  are  at  Neelysville,  Danville,  and  La  Salle.  The  lat- 
ter is  of  importance  from  its  proximity  to  Chicago.  There  are  three 
workable  beds,  VI,  4±  to  5  ft. ;  V,  3  to  9  ft.,  usually  6  ft. ;  II,  4  ft. 
The  coal  of  the  upper  bed,  No.  VI,  is  light,  dry,  and  free-burning. 
No.  V  is  a  purer  coal.  No.  II  is  most  highly  bituminous,  cakes  in 
burning,  is  high  in  sulphur,  and  throws  off  heavy  soot.  In  the  Wil- 
mington district,  Will  Co.,  there  is  a  workable  seam  of  coal  which  is 
largely  used  for  household  and  steam  purposes.  The  Illinois  coals  are 
generally  high  in  moisture,  and  are  often  very  high  in  sulphur  and 
ash.  When  burned  in  ordinary  furnaces  they  produce  great  volumes 
of  black  smoke.  Recent  analyses  of  Illinois  coals  (says  "Mineral  Re- 
sources," 1910)  show  them  to  contain  an  average  of  about  12  per  cent 
moisture,  10  per  cent  ash,  37  per  cent  volatile  matter,  39  per  cent  fixed 
carbon,  and  3  per  cent  sulphur.  The  proportions  vary  from  region  to 
region,  and  even  from  mine  to  mine.  The  estimated  coal  supply  of  the 
State  in  1910  is  about  230,000,000,000  tons,  or  sufficient  to  last  about 
3000  years  at  the  present  rate  of  production,  allowing  one-third  for 
waste. 

Range  of  Variation  in  Illinois  Coal. — The  St.  Louis  tests  show  a 
range  of  heating  value  of  six  samples  of  Illinois  coal  of  from  13,767 
to  14,674  B.T.U.  per  Ib.  combustible,  or  less  than  7  per  cent.  The 
figures  in  the  following  table,  omitting  Nos.  9a,  25a  and  28a,  which 
are  probably  erroneous,  range  from  13,469  to  14,830  B.T.U.  per  Ib. 
combustible,  or  10.1  per  cent  of  the  smaller  value. 

A  large  table  of  Illinois  Coals  by  Counties  published  by  the  Green 
Engineering  Co.,  gives  for  each  of  40  counties  the  average,  maximum 
and  minimum  figures  of  heating  value  in  B.T.U.  per  Ib.,  moisture, 
ash,  volatile  matter  and  fixed  carbon,  with  the  number  of  analyses 


COAL-FIELDS   OF    THE   UNITED  STATES 
ILLINOIS  COALS.* 


123 


No. 

County. 

Town. 

Air-dry  Coal. 

Pure  Coal. 

B 

1 

Moist- 
ure. 

Ash. 

Sul- 
phur. 

Volatile 
Matter. 

Fixed 
Carbon. 

B.T.U. 
per 
Pound. 

1 
2a 
26 
3a 
36 
4a 
46 
5a 
56 
6 
7 
8 
9a 
96 
lOa 
106 
lla 
116 
12 
13 
14a 
146 
15a 
156 
16a 
166 
17o 
176 
18o 
186 
19a 
196 
20 
21 
22 
23a 
236 
24 
25a 
256 
26<z 
266 
27 
28a 
286 
29 
30a 
306 

Bureau  

Christian  .  .  . 

<  t 

Clinton  .... 

<  i 

Fulton.  .  . 

1  1 

Grundy  

Henry  
Jackson. 

Ladd 

2 
6 
1 
7 
6 
5 
5 
2 
2 
6 
1 
6 
7 
7 
2 
5 
5 
5 
3 
5 
6 
6 
6 
6 
6 
6 
2 
2 
5 
5 
1 
1 
2 
2 
6 
6 
6 
6 
5 
5 
6 
5 
5 
7 
7 
2 
7 
7 

6.60 

8.06 
7.74 
9.47 
8.10 
11.78 
7.70 
11.44 
9.70 
9.99 
4.96 
10.16 
7.68 
5.52 
10.26 
6.57 
10.44 
10.64 
5.64 
11.01 
9.62 
10.24 
7.76 
8.26 
8.52 
5.51 
10.94 
10.31 
10.37 
9.46 
7.84 
9.60 
9.22 
8.04 
7.24 
8.68 
7.17 
8.12 
3.70 
5.68 
10.42 
12.56 
9.19 
9.90 
8.00 
11.44 
6.35 
5.00 

8.04 
18.66 
12.72 
15.28 
14.24 
14.18 
9.77 
5.36 
31.18 
7.03 
4.39 
25.00 
8.50 
5.40 
12.02 
10.00 
8.58 
15.00 
16.46 
15.16 
14.55 
5.30 
14.40 
11.06 
9.82 
11.94 
2.32 
13.14 
19.20 
8.11 
18.39 
8.82 
5.96 
7.80 
10.04 
7.73 
13.15 
16.21 
15.80 
8.90 
6.46 
9.93 
10.16 
5.02 
19.47 
4.26 
17.80 
10.62 

2.70 
3.45 
2.60 
1.12 
3.40 
1.93 
3.10 
2.10 
3.55 
2.57 
0.62 
2.48 
3.24 
3.07 
2.96 
2.20 
2.44 
3.17 
3.10 
3.35 
3.86 
1.98 
4.74 
3.09 
3.00 
2.60 
0.79 
2.67 
3.13 
2.41 
4.78 
3.02 
1.77 
3.13 
3.04 
3.07 
3.13 
4.00 
2.40 
1.18 
2.73 
2.14 
1.47 
2.00 
3.40 
1.95 
1.14 
2.22 

45.24 
48.91 
45.59 
39.84 
43.78 
44.84 
47.48 
44.58 
46.56 
45.79 
38.20 
48.10 
48.69 
47.26 
47.01 
47.22 
48.01 
49.46 
48.85 
46.74 
45.11 
47.31 
47.44 
47.52 
45.43 
44.59 
42.18 
43.75 
47.02 
45.64 
49.79 
48.25 
45.67 
48.87 
46.81 
44.34 
43.55 
46.83 
41.17 
39.02 
47.54 
43.99 
45.65 
47.90 
48.02 
43.04 
53.80 
37.64 

54.76 
51.09 
54.41 
60.16 
56.22 
55.16 
52.52 
55.42 
54.54 
54.21 
61.80 
51.90 
51.31 
52.74 
52.99 
52.78 
51.99 
50.54 
51.15 
53.26 
54.89 
52.69 
52.56 
52.48 
54.57 
55.41 
57.82 
56.25 
52.98 
54.36 
50.21 
51.75 
54.33 
51.13 
53.19 
55.56 
56.45 
53.17 
58.83 
60.98 
52.46 
56.01 
54.35 
52.10 
51.98 
56.96 
46.20 
62.36 

13,793 
13,694 
14,641 
13,663 
14,416 
14,238 
14,576 
14,412 
14,623 
13,584 
14,653 
14,157 
12,535 
14,661 
13,917 
14,677 
13,546 
14,614 
14,617 
13,469 
13,626 
14,434 
14,130 
14,556 
13,638 
14,560 
13,995 
14,331 
13,914 
14,255 
13,748 
14,446 
14,265 
14,153 
14,250 
13,786 
14,344 
13,892 
13,150 
14,830 
13,750 
14,326 
13,959 
12,162 
14,617 
13,406 
13,834 
14,607 

Pana 

Assumption  .  .  . 
Trenton 

Breese  .  .  . 

Norris  
Cuba  
So.  Wilmington 
Braceville  
Kewanee 

Murphy  sboro.  . 
Etherly  
Kangley  
Streator  
Cardiff  
Fairbury  

Lincoln  

i  ( 

Bloomington.  . 
Niantic.  
Mt.  Olive  
Greenridge.  .  .  . 
Edwardsville  .  . 
Collinsville.  .  .  . 
Odin  
Sandoval  

Wenona  

1  1 

Knox  

La  Salle  

<  < 

Livingston  .  . 
Logan  

McLean  .... 
Macon  

Macoupin.  .  . 

<  < 

Madison.  .  .  . 

1  1 

Marion  

Marshall.  .  .  . 

<  < 

Menard  
Mercer  

Montgomery 
Peoria. 

Middletown.  .. 
Greenview.  .  .  . 
Sherrard.  .  . 

<  < 

Litchfield  .  ! 
Holies  
Du  Quoin  

Tilden  

<  < 

Perry  
Randolph.  .  . 

St.  Clair.'.  .". 

Saline  

i  i 

Sangaraon  .  . 

<  < 

Shelby.  ...'.' 

Vermillion  .  . 

1  1 

Will  .". 

French  Village 
Eldorado  
Harrisburg.  .  .  . 
Auburn  
Dawson  

Moweaqua.  .  .  . 
Catlin  
Danville  
Braid  wood.  .  .  . 
Lauder  

Williamson  . 

<  < 

Herrin 

*  From  Bulletin  No.  3  of  the  Illinois  Geological  Survey. 


124 


STEAM-BOILER  ECONOMY. 


for  each  county  from  which  the  average  maximum  and  minimum 
figures  are  given.  The  range  of  figures  for  the  40  counties  are  as 
follows : 


Heating  Value 
Per  Ib. 

Moisture. 

Ash. 

Volatile 
Matter. 

Fixed 
Carbon. 

Maximum. 
Minimum  . 
Average  .  . 

10,137  to  13,252 
6,316  to  11,372 
9,746  to  11,  779 

5.  20  to  16.30 
1.12  to  10.64 
2.67  to  14.10 

9.  22  to  38.  80 
1.20  to  15.30 
4.80  to  21.  47 

28.  96  to  46.  00 
18.  40  to  36.15 
26.  97  to  39.  77 

46.  87  to  66.50 
30.  00  to  52.61 
41.  33  to  56.  04 

The  table  is  to  be  interpreted  thus :  In  40  counties  the  maximum 
heating  value  of  all  the  samples  tested  ranged  from  10,137  to  13,252 
B.T.U.  per  Ib.,  and  the  minimum  value  from  6316  to  11,372,  etc. 
The  highest  heating  value  in  the  whole  state  is  13,252  B.T.U.  per  Ib., 
and  the  lowest,  6316,  is  less  than  half  the  highest.  The  moisture 
ranges  from  1.12  to  16.30%  and  the  ash  from  1.20  to  .38.80%. 
The  table  would  have  been  more  useful  if  it  had  given  the  maximum, 
minimum  and  average  values  of  the  heating  value  per  Ib.  of  com- 
bustible for  each  county,  together  with  the  maximum,  minimum 
and  average  figures  for  ash  and  moisture,  for  each  county. 

For  the  purpose  of  valuing  a  certain  carload  or  cargo  of  coal  as 
received,  the  heating  value  per  Ib.  of  an  average  sample  is  im- 
portant, but  for  the  purpose  of  studying  the  coals  of  a  district  and 
comparing  them  with  coals  of  another  district,  the  proximate  analysis 
and  the  heating  value  of  the  coal  as  received,  are  unimportant,  except 
in  that  these  furnish  the  basis  for  the  calculation  of  the  heating 
value  per  Ib.  of  combustible  and  the  ratio  of  volatile  matter  to  the 
total  combustible,  which  together  with  the  average  moisture  and  ash 
in  the  coals  as  received  are  the  data  most  needed  for  comparison. 


THE  MISSOURI  COAL-BASIN. 

(Iowa,  southeastern  Nebraska,  Missouri,  eastern  Kansas,  Arkansas,  Oklahoma, 

Texas.) 

The  separation  of  the  Western  coal-field,  of  which  Missouri  forms 
an  important  part,  from  the  Illinois  or  Central  field  is  made  by  the 
Mississippi  River  and  its  immediate  valley.  At  one  place  near  the 
northern  border  of  the  Illinois  field  the  present  course  of  the  Missis- 
sippi cuts  through  it,  a  small  portion  of  the  Central  field  being  found 
across  the  river  in  Iowa.  The  two  fields  are  really  the  same,  the 
barren  valley  being  a  narrow  one,  and  in  it  isolated  bodies  of  coal  are 
found  both  in  Iowa  and  Missouri.  It  has  been  customary,  however, 
to  consider  them  separately. 


COAL-FIELDS  OF  THE  UNITED  STATES. 


125 


Iowa. —  The  Missouri  coal-basin  occupies  nearly  one-half  of  the 
State.  The  coal-measures  are  divided  into  upper,  middle,  and  lower, 
the  latter  of  which  contains  the  productive  seams,  two  in  number. 
They  are  of  irregular  thickness,  sometimes  reaching  5  ft.  An  average 
of  64  analysis  made  by  the  State  geologist  gives:  Moisture,  8.57; 
Volatile  matter,  39.24;  Fixed  carbon,  45.42;  Ash,  6.77. 

Four  analyses  by  Forsyth,  given  below,  show  a  wide  range  of 
quality : 


Locality. 

Water. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Volatile 
Matter, 
per  cent 
of  Com- 
bustible. 

Chisolm  

9    18 

40.42 

39  58 

10  82 

50  5 

Flagler's 

9  48 

40  16 

37  69 

12  31 

51  6 

Hiteman  

4.99 

35.27 

25.37 

34  37 

58  0 

Keb 

9  81 

37  49 

44  75 

7  95 

45  6 

The  coal  from  Hiteman  appears  to  be  a  cannel-coal  very  high  in 
ash.  The  coal-bearing  formations  of  Iowa  cover  an  area  of  approx- 
imately 20,000  square  miles,  of  which  13,000  may  be  considered  poten- 
tially productive  under  present  conditions  and  considerably  more  in 
future  periods  when  the  fuel  supplies  of  the  world  shall  have  suffered 
greater  depletion.  The  total  coal  remaining  is  estimated  at  nearly 
29,000,000,000  tons,  or  about  2400  times  the  exhaustion  in  1910. 


Missouri. — The  coal-measures  are  contained  chiefly  in  the  north- 
ern and  western  portions  of  the  State.  An  arm  of  this  territory,  how- 
ever, follows  the  course  of  the  Missouri  River  eastward  for  a  short  dis- 
tance in  the  central  part  of  the  State,  and  some  coal  is  also  found  in 
the  vicinity  of  St.  Louis.  The  total  area  included  is  estimated  at  about 
25,000  square  miles,  distributed  over  fifty-seven  counties  in  whole  or 
in  part.  All  of  the  coals  are  of  the  bituminous  variety,  with  the  ex- 
ception of  some  limited  deposits  which  approach  cannel-coal  in  char- 
acter. The  bituminous  coals  have,  as  a  rule,  a  high  percentage  of  ash 
compared  with  the  best  coals  of  this  character.  They  are  compara- 
tively soft,  and  deteriorate  by  exposure  or  much  handling.  They  also 
usually  carry  considerable  sulphur  in  the  form  of  pyrites. 

There  are  16  seams  in  three  measures,  of  which  seven  are  of  work- 
able thickness.  Analyses,  by  C.  G.  Brodhead,  are  as  follows: 


126 


STEAM-BOILER  ECONOMY. 


ANALYSES  OF  MISSOURI  COALS. 


County. 

Moisture. 

Volatile. 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Vol.  Mat. 
%of 
Comb. 

Ray  .  :  

10  05 

38  55 

45  40 

A  on 

241 

A  r    Q 

Pettis  

3  95 

33  10 

46  26 

1«    AQ 

4  41 

4o.y 

41    7 

St.  Louis  
Henry  
La  Fayette  
Johnson  

9.55 
5.14 
6.36 
7  29 

38.28 
37.91 
36.28 
42  27 

42.99 
46.82 
47.80 
46  95 

9.18 
10.13 
9.56 

Q    4Q 

11  .  / 
47.1 
44.7 
43.1 

47   A 

Lincoln  

8  50 

39  50 

46  45 

^    ^ 

0    AQ 

AK.     Q 

Carroll  
Saline  

2.97 
6  02 

36.36 
40  33 

47.83 
42  09 

12.84 

USA 

43.2 

40     Q 

Livingston  
Nodaway  

5.38 
3  53 

42.27 
42  72 

44.98 
40  71 

7.37 
13  04 

48.4 

ci    o 

Callaway  ...    . 

7  43 

38  90 

45  85 

7  82 

4C     Q 

Andrew  
Cass  

8.94 
7  80 

34.75 
33  20 

45.38 
55  75 

10.93 
3  25 

43.4 

07   q 

Charlton  

5  82 

38  01 

54  53 

1  64 

•      .     .      . 

41    1 

Macon  

12.05 

40.75 

43.50 

3.70 

48.4 

On  account  of  the  relatively  poor  quality  of  the  Missouri  coal  as 
compared  with  that  of  Illinois  its  production  has  been  restricted  to 
the  needs  of  local  markets.  The  annual  tonnage  increased  from 
2,240,000  short  tons  in  1882  to  4,238,586  tons  in  1903.  In  1909  the 
production  was  3,756,530  tons,  and  in  1910,  2,982,433,  the  decrease  in 
1910  being  due  to  a  long  strike  of  the  miners.  The  coal  supply  of 
the  State  is  estimated  to  approximate  40,000,000,000  tons. 

Kansas. — The  '  Kansas  coal-measures  form  a  part  of  the  great 
Western  field  which  passes  through  the  eastern  half  of  the  State  from 
Iowa  and  Missouri  into  the  Indian  Territory,  with  an  outlying  area  of 
cretaceous  lignite  to  the  west  and  in  the  northern  central  part  of  the 
State.  The  main  portion  of  the  field  occupies,  approximately,  one- 
fourth  the  area  of  the  State. 

The  coal-measures  consist  of  three  kinds  of  rock  formations — 
sandstones,  limestones,  and  shales.  In  these  are  inclosed  the  beds  of 
coal,  which  do  not  occupy  anywhere  more  than  one-twentieth  of  the 
thickness  assigned  to  the  coal-measures,  and  over  large  parts  of  the 
area  there  is  no  coal  at  all.  A  few  square  miles,  with  one  bed  of  coal 
30  inches  thick,  would  be  a  rich  district,  and  there  are  several  such 
districts  in  eastern  Kansas.  The  bottom  of  the  lower  coal-measures  is 
the  richest  horizon  of  the  formations.  It  is  in  this  horizon,  not  far 
from  the  Spring  River  boundary,  that  we  have  the  Weir  City  and 
Scammon  coal-field,  of  Cherokee  County,  and  the  neighboring  coal- 
fields of  Frontenac  and  Pittsburg,  in  Crawford  County.  The  thickest 
and  best  seam  of  coal  in  Kansas  is  the  Cherokee  bed,  found  in  Chero- 


COAL-FIELDS  OF  THE  UNITED  STATES. 


127 


kee,  Crawford  and  Labette  counties.  It  extends  from  Oklahoma, 
entering  the  State  near  Chetopa,  and  runs  across  the  southeast 
part  of  Labette  County,  the  west  and  northwest  parts  of  Cherokee, 
and  southeast  part  of  Crawford,  and  enters  Missouri.  A  few  miles 
north  of  Columbus  the  coal-mining  region  begins,  and  we  have  a 
series  of  mining  towns — Scammon,  Weir  City,  Cherokee,  Fleming, 
Frontenac,  Pittsburg,  Arcadia,  Minden — around  which  the  coal  seam, 
whose  average  thickness  is  over  40  inches,  is  worked.  About  91  per 
cent  of  the  total  production  of  the  State  is  mined  in  this  district. 
The  coal  is  of  a  better  grade  than  that  found  in  adjacent  States. 

A  second  important  district  is  that  adjacent  to  Leavenworth  and 
Atchison  in  the  northeastern  part  of  the  State,  where  a  thin  bed 
is  found.  It  produces  about  6  per  cent  of  the  total  output  of  the 
State.  A  third  district  yielding  about  3  per  cent  of  the  total  is 
that  of  Osage  and  adjacent  counties,  in  which  a  bed  20  to  22 
inches  thick  is  mined.  The  total  supply  of  the  State  is  estimated 
to  approximate  7,000,000,000  tons. 

The  following  figures  showing  the  range  of  analyses  and  heating 
values  of  Kansas  coals  are  from  Engineering  Bulletin  No.  3  of  the 
University  of  Kansas,  1913. 


Number  of  Samples. 

Southern  Kansas 
Coals. 

Central  Kansas 
Coals. 

Leavenworth 
Coals. 

Volatile   matter,    per   cent   of 
combustible  
Moisture  in  coal  

33.05  to  39.  80 
1.05  to    4  95 

37.  50  to  45.  05 
5  10  to    8  00 

38.  40  to  42.30 
1  90  to    9.10 

Ash  in  drv  coal  

7  .  05  to  28  .  20 

7  .  20  to  14  .  05 

6  .  40  to  22  .  40 

Sulphur  in  dry  coal 

2  46  to    7  07 

3  12  to    6  52 

2  56  to    5  40 

B.T.U.  per  Ib.  combustible..  .  . 

13,660  to  14,850 

12,000  to  12,960 

12,730  to  14,580 

Arkansas. — The  coal-measures  cover  an  area  of  9043  square  miles 
along  the  course  of  the  Arkansas  River  in  the  western  part  of  the 
State.  Two  beds  have  been  opened,  but  only  the  lower  is  of  workable 
thickness.  The  best  coal  yet  found  in  the  State  is  the  Spadra,  in 
Johnson  County,  3l/2  feet  thick  in  some  places.  The  following  analy- 
ses are  given  by  Macfarlane : 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Vol.  Mat. 
%  of  Comb. 

Sebastian  Co 

1.40 

12.35 

82.25 

4.00 

13^1 

Long's  

3.80 

10.70 

84.10 

1.40 

11.3 

Yell  Co  
Johnson  Co.  (11  in.). 
Crawford  Co.(lft.j  . 
Spadra  Creek  

3.00 
2.00 
1.00 
0.50 

11.40 
7.75 
15.20 
7.90 

80.40 
88.75 
80.80 
85.60 

5.20 
1.50 
3.00 
6.00 

12.4 
8.0 
15.8 
8.4 

128 


STEAM-BOILER  ECONOMY. 


The  Arkansas  coals  range  from  semi-anthracite  in  the  eastern  part 
of  the  field  to  lignite  in  the  western. 

Arkansas  coals  are  all  more  or  less  soft  and  friable,  and  not  well 
adapted  to  long  transportation.  The  characteristic  is  variable  in 
different  openings.  They  all  burn  freely  and  make  little  smoke  or 
soot.  For  reaching  the  best  results,  however,  a  grate  with  small 
openings  is  necessary,  as  these  coals  are  liable  to  decrepitate  and  to 
fall  through  the  grate. 

The  production  of  coal  in  Arkansas  was  1,205,479  short  tons  in 
1898,  2,670,438  tons  in  1907,  and  1,905,958  tons  in  1910.  The 
remaining  supply  in  1910  is  estimated  at  approximately  1,750,000,000 
tons  of  bituminous  and  semi-anthracite,  and  90,000,000  tons  of  lig- 
nite. The  lignite  areas  have  not  been  developed. 

Oklahoma. — The  total  area  underlain  by  workable  coal  is  estimated 
at  10,000  square  miles.  At  present  the  entire  production  is  from 
what  were  formerly  known  as  the  Cherokee,  Creek  and  Choctaw 
nations  of  Indian  Territory,  the  last  named  contributing  by  far  the 
largest  portion.  H.  M.  Chance  (Trans.  A.  I.  M.  E.,  1890)  says: 

The  Choctaw  coal-field  is  a  direct  westward  extension  of  the 
Arkansas  coal-field,  but  its  coals  are  not  like  Arkansas  coals,  except 
in  the  country  immediately  adjoining  the  Arkansas  line. 

In  the  Mitchell  basin,  about  10  miles  west  from  the  Arkansas  line, 
coal  recently  opened  shows  19  per  cent  volatile  matter;  the  Mayberry 
coal,  about  8  miles  farther  west,  contains  23  per  cent  volatile  matter ; 
and  the  Bryan  Mine  coal,  about  the  same  distance  west,  shows  26  per 
cent  volatile  matter.  About  30  miles  farther  west,  the  coal  shows 
from  38  to  41|  per  cent  volatile  matter,  which  is  also  about  the  per- 
centage in  coals  of  the  McAlester  and  Lehigh  districts. 


ANALYSES  OF  OKLAHOMA  COALS. 


Water. 

Volatile 
Matter. 

Fixed 

Carbon. 

Ash. 

Sulphur. 

Mitchell  Basin  
Grady  Basin.  .  .  
McKinnev  District  
Krebs,  McAlester  Bed  
Lehigh  mines  

1.06 
1.79 
1.71 
1.80 
4.32 

19.03 

40.21 
38.67 
37.17 
40.51 

71.74 
51.79 
51.48 
53.40 

48.47 

7.53 
4.88 
7.14 
6.73 
8.10 

0.65 
1.33 
1.01 
0.90 
2.60 

Atoka  

6.66 

35.42 

57.52 

6.60 

•    3.73 

Choctaw  Nation  
Cherokee 

1.59 
3  62 

23.31 
29.51 

66.85 
48.09 

8.25 
14.78 

1.18 
4  00 

i  < 

4.07 

27.67 

42.12 

20.20 

5.94 

COAL-FIELDS  OF  THE   UNITED  STATES. 


129 


"Mineral  Resources"  for  1889  says  of  the  coals  of  the  McAlester 
bed  mined  at  McAlester,  Krebs,  and  Alderson,  and  the  Grady  bed 
mined  at  Hartshorne,  "These  coals  compare  favorably  with  the  best 
gas-coals  mined  in  the  country  (as  comparison  with  standard  Pitts- 
burg  coal  will  show),  and  they  are  by  far  the  best  coals  now  mined  in 
the  Southwest,  if  not  indeed  the  best  mined  west  of  the  Mississippi 
River.  They  are  in  every  way  vastly  superior  to  Kansas,  Missouri, 
and  Iowa  coals." 

Texas. — A  detached  portion  of  the  great  Missouri  coal-field  covers 
the  northeastern  portion  of  the  State  for  about  6000  square  miles.  The 
coal  is  a  regular  bituminous  of  the  Carboniferous  age.  Some  beds 
are  from  3  ft.  to  6  ft.  thick.  The  coal  is  usually  of  poor  quality,  high 
in  ash  and  sulphur.  Three  analyses  gave  the  following : 


Localities. 

Moisture. 

Vol.  Mat. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Younji  Co 

10  00 

30  75 

46  59 

11  96 

0  70 

Fort  Worth 

14  42 

30  03 

42  53 

13  02 

1  47 

it         it 

4  60 

34  72 

49  27 

11  41 

1  56 

Analyses  by  Dr.  W.  B.  Phillips  (Min.  Res.,  1910)  show  a  much 
greater  range  of  composition.  Eleven  coals  show  moisture  from  2.8 
to  11.0  per  cent,  ash  (in  the  dry  coal)  3.07  to  26.34  per  cent,  volatile 
matter,  per  cent  of  combustible,  nine  coals,  40.4  to  47.4  per  cent,  one 
57.0  and  one  58.7  per  cent,  the  two  last  being  cannel-coal,  containing 
5.65  and  5.72  per  cent  hydrogen  in  the  dry  coal  with  10.03  and  12.18 
per  cent  oxygen,  3.00  and  2.50  per  cent  nitrogen,  and  2.25  and  2.09 
per  cent  sulphur.  One  of  the  coals  had  as  high  as  4.24  per  cent 
sulphur. 

Cannel-coal  and  semi-anthracite  have  also  been  found  in  Texas. 
In  the  Cretaceous  and  Laramie  coal-fields  of  the  Rio  Grande,  near 
Eagle  Pass,  bituminous  coal  of  good  quality  is  found.  It  is  superior 
to  the  Carboniferous  coals  of  the  State,  but  to  the  eastward  the  beds 
are  lignite  and  impure.  Lignites,  mostly  of  very  poor  quality,  con- 
taining 10  to  20  per  cent  moisture  even  when  sun-dried,  are  found  in 
many  deposits  in  the  eastern  part  of  the  State.  The  San  Tomas, 
Webb  Co.,  coal,  which  has  the  appearance  of  being  an  altered  lignite, 
is  a  very  serviceable  fuel,  and  is  largely  used  in  Laredo  and  on  the 
Mexican  National  Railroad. 

The  estimated  supply  of  bituminous  coal  in  Texas  approximates 


130 


STEAM-BOILER  ECONOMY. 


8,000,000,000  short  tons  and  of  lignite  23,000,000,000  tons.  The 
production  in  1910  was  bituminous  978,498  tons;  lignite  864,858  tons. 
Bulletin  No.  189  of  the  University  of  Texas,  1911,  on  "The  Com- 
position of  Texas  Coals  and  Lignites,"  gives  analyses  and  heating 
values  of  about  50  samples  of  Texas  coals  from  different  districts. 
They  show  a  wide  range  of  variation  in  composition.  In  17  samples 
taken  at  the  mines  the  moisture  ranged  from  3.46  to  13.44  per  cent, 
averaging  7.40  per  cent.  In  21  samples  received  from  mining  com- 
panies the  moisture  was  from  2.30  to  11.00  per  cent,  averaging  5.82 
per  cent.  Some  of  these  may  have  been  partially  air-dried.  The 
following  analyses  of  dried  coal  are  selected  to  show  the  range  of 
composition.  Figures  in  the  second  place  of  decimals  are  omitted 


* 

1 

C3 

•-S 

. 

1 

O 

"S 

a! 

|5 

a 

<B  0) 

a 

O 

..a 

•  *'l 

5a 

6 

3 
o 

1 

•a 

^U 

£ll 

|| 

* 

£ 

00 

d 

W 

d 

fc 

PQ 

« 

^ 

3 

54.0 

38.0 

8.0 

2.3 

71.0 

5.7 

10.0 

3.0 

13,190 

12,315 

2.30 

5 

39.2 

57.7 

3.1 

1.8 

74.7 

5.1 

13.7 

1.6 

12,420 

11,500 

8.20 

43 

29.9 

38.6 

31.5 

0.6 

51.2 

3.7 

11.8 

1.2 

12,980 

10,600 

3.64 

1518 

50.0 

40.6 

9.4 

2.6 

69.5 

5.6 

11.3 

1.5 

14,180 

11,052 

4.09 

1520 

36.5 

44.3 

19.2 

1.4 

64.1 

4.6 

8.9 

1.8 

14,300 

11,149 

9.40 

1528 

33.0 

40.9 

26.1 

5.0 

60.3 

4.1 

2.6 

1.8 

15,400 

11,171 

5.31 

Av.  of  17 

37.2 

45.1 

17.3 

2.4 

64.8 

4.6 

9.0 

1.9 

14,560 

11,245 

7.40 

Av.  of  21 

39.1 

43.6 

17.3 

2.0 

62.8 

4.7 

11.0 

2.3 

13,580 

10,558 

5.82 

No.  3,  Cannel  Coal,  Webb  Co.,  Nos.  5  and  1520,  Eagle  Pass,  Maverick  Co. 
No.  43,  Olmos  run-of-mine.  1518,  Minera,  Webb  Co.  1528,  Keeler,  Palo 
Pinto  Co. 

*  Calculated  from  the  ultimate  analyses.  t  By  Parr  calorimeter. 

The  analysis  and  the  heating  value  of  No.  1528  are  remarkable,  and 
indicate  it  to  be  cannel  coal.  The  figure  obtained  by  the  Parr  calori- 
meter, reduced  to  combustible,  is  15,970. 

The  composition  of  the  ash  of  Texas  coal  varies  widely.  Analyses 
of  the  ash  from  the  17  mine  samples  gave:  Silica  29.1  to  65.3,  av. 
46.0 ;  alumina  13.1  to  41.1,  av.  25.9  ;  oxide  of  iron  4.0  to  28.0,  av.  16.1 ; 
lime,  trace  to  22.1,  av.  6.0;  magnesia  0  to  2.3,  av.  0.7;  sulphuric  acid, 
trace  to  15.0,  av.  4.4. 

The  Bulletin  above  named  states  that  there  are  three  well- 
recognized  coal  fields  in  Texas,  two  on  the  Rio  Grande  and  one  in 
North  Central  Texas,  west  of  Fort  Worth.  The  two  on  the  Rio 
Grande  are  in  Maverick  Co.,  with  Eagle  Pass  as  the  chief  town,  and 


COAL-FIELDS  OF   THE   UNITED  STATES. 


131 


Webb  Co.,  with  Laredo  as  the  chief  town.  The  total  workable  coal 
area  is  about  8200  square  miles,  with  an  additional  area  of  5300  square 
miles  that  may  contain  workable  beds.  The  production  of  the  Rio 
Grande  fields  in  1910  was  215,328  tons,  and  that  of  the  north  central 
field  913,619  tons.  The  total  production  of  lignite  in  the  State  in 
1910  was  979,232  tons;  and  it  is  rapidly  increasing.  For  analyses  of 
lignites  see  page  137. 

GOALS  WEST  OF  THE  NINETY-SEVENTH  MERIDIAN. 

Colorado  Coals. — The  Colorado  coals  are  of  extremely  variable  com- 
position, ranging  all  the  way  from  lignite  to  anthracite.  Gr.  C.  Hewitt 
(Trans.  A.  I.  M.  E.,  xvii.  377)  says:  The  coal-seams,  where  unchanged 
by  heat  and  flexure,  carry  a  lignite  containing  from  5  to  20  per  cent 
of  water.  In  the  southeastern  corner  of  the  field  the  same  have  been 
metamorphosed  so  that  in  four  miles  the  same  seams  are  an  anthra- 
cite, coking  and  dry  coal.  In  the  basin  of  Coal  Creek  the  coals  are 
extremely  fat,  and  produce  a  hard,  bright,  sonorous  coke.  North  of 
Coal  Basin  half  a  mile  of  development  shows  a  gradual  change  from  a 
good  coking  coal  with  patches  of  dry  coal  to  a  dry  coal  that  will  barely 
agglutinate  in  a  beehive  oven.  In  another  half  mile  the  same  seam  is 
dry.  In  this  transition  area,  a  small  cross-fault  makes  the  coal  fat  for 
twenty  or  more  feet  on  either  side.  The  dry  seams  also  present  wide 
chemical  and  physical  changes  in  short  distances.  A  soft  and  loosely 
bedded  coal  has  in  a  hundred  feet  become  compact  and  hard  without 
the  intervention  of  a  fault.  A  couple  of  hundred  feet  has  reduced  the 
water  of  combination  from  12  to  5  per  cent. 

ANALYSES    OF    COLORADO    COALS. 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Sunshine,  Colo.,  average.  .  .  . 
Newcastle  "  " 

2.8 
1  7 

36.3 
37  95 

37.1 

48  6 

23.8 
11.6 



El  Moro  "  '  ' 

1  32 

38  23 

55.86 

3.59 

Crested  Buttes,  "  .... 
Lenox,  Huerfano  Co  
Rouse,  "  
Chicosa,  Las  Animas  Co.  .  .  . 
Victor.  "  "  ... 
Fan-mount  vein,  La  Plata  Co. 
Porter  vein,  La  Plata  Co  .  .  . 

1.10 
2.92 
2.66 
0.20 
1.26 
1.25 
0.63 

23.20 
41.18 
36.71 
28.94 
36.40 
39.71 
34.70 

72.60 
45.36 
51.41 
64.51 
53.10 
52.90 
57.30 

3.10 
10.54 
9.22 
6.35 
9.24 
6.14 
7.37 

'i.'ag' 

1.37 
0.27 

1.11 

0.74 

The  Trinidad-Raton  coal  field,  the  Colorado  portion  of  which  is 
located  in  Las  Animas  County  (the  southern  part  of  the  field  is  in 
New  Mexico)  is  the  most  important  producer  in  the  State.  Las 


132 


STEAM-BOILER  ECONOMY. 


Animas  County  produces  nearly  50  per  cent  of  Colorado's  total,  which 
was  11,973,736  short  tons  in  1910.  The  coal  fields  in  Colorado  lie 
along  the  lower  flanks  and  among  the  foot  hills  of  the  mountains,  in 
three  groups  known  as  the  eastern,  the  park,  and  the  middle  groups. 
—"Mineral  Resources,"  1910. 

In  production  of  coal,  Colorado  ranks  first  among  the  States  west 
of  the  Mississippi  River,  and  seventh  among  all  the  coal-producing 
States.  The  estimated  total  supply  in  1910  is  371,500,000,000  tons, 
equal  to  about  740  times  the  production  of  the  whole  United  States  in 
that  year. 

New  Mexico. — The  coals  of  New  Mexico,  like  most  of  those  of 
the  Rocky  Mountain  region,  are  of  cretaceous  age  and  vary  from 
anthracite  to  sub-bituminous.  The  former  occupies  only  limited 
areas  and  its  production  is  less  than  2  per  cent  of  the  total.  Of 
the  total  coal  production  of  the  State  (3,508,321  tons  in  1910), 
over  75  per  cent  was  from  the  Raton  field  in  Colfax  county,  the 
southern  extension  of  the  Trinidad  field  of  Colorado.  The  coal  of 
this  field  is  a  true  coking  coal.  There  are  several  small  detached 
areas  in  the  southeastern  portion  of  the  State  which  contain  bitu- 
minous coal,  and  in  the  northwestern  part  of  the  State,  covering 
portions  of  Rio  Arriba,  San  Juan  and  McKinley  counties  and  con- 
taining the  producing  districts  of  Gallup  and  Monero.  There 
is  a  large  area  of  coal,  chiefly  sub-bituminous  ("black  lignite").  At 
Monero  the  coal  is  bituminous.  The  estimated  quantity  of  coal  in 
the  ground  in  1910  (not  including  fields  whose  boundaries  are 
unknown)  is  163,700,000,000  tons. 

ANALYSES. 


Water. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

White  Oaks,  Lincoln  Co  
Vermejo  Pass  
Placer  anthracite  

2.35 
3.27 
2.90 

35.53 
23.73 
3.18 

50.24 
59.72 

88.91 

11.88 
13.28 
5.21 

0.61 

Wyoming. — About  50  per  cent  of  the  area  of  the  State  is 
underlain  by  coal-bearing  formations,  and  the  estimated  tonnage 
of  the  coal  in  the  ground  exceeds  that  of  an}7  other  State  with  the 
possible  exception  of  North  Dakota.  The  largest  field  is  the  Powder 
River  field  between  the  Black  Hills  and  the  Bighorn  Mountains. 
It  is  the  southern  extension  of  the  great  Fort  Union  coal  region 
of  Montana  and  North  Dakota,  and  extends  from  the  North  Platte 


COAL-FIELDS  OF  THE  UNITED  STATES.  133 

Eiver  to  the  Montana  line.  Of  the  total  area  of  about  15,000 
square  miles  at  least  11,000  square  miles  is  underlain  by  coal  beds 
more  than  3  ft.  thick.  The  next  largest  field  is  the  Green  Eiver 
Basin,  in  the  southwestern  part  of  the  State,  at  least  4800  square 
miles  of  which  contains  workable  coal.  Other  and  smaller  fields 
are  Bighorn  Basin,  Wind  River  Basin,  Hannah,  Ham's  Fork  and 
Mount  Leidy. 

The  coal-bearing  formations  extend  from  the  base  of  the  upper 
Cretaceous  to  near  the  middle  of  the  Tertiary.  As  a  rule  the  older 
the  formation  the  better  the  coal.  The  coal  mined  in  Wyoming 
is  bituminous  and  sub-bituminous.  The  estimated  total  supply  in 
1910  is  nearly  424,000,000,000  short  tons,  or  over  800  times  the 
rate  of  production  in  the  whole  United  States  in  1910. 

Analyses  and  heating  values  of  various  coals  in  Wyoming  are  given 
on  pages  69  and  160. 

Montana. — The  coals  of  Montana  are  all  of  Cretaceous  age.* 
They  embrace  a  wide  variety  of  true  bituminous  coals,  found  only 
in  or  near  the  mountains,  and  the  inferior  lignites  whose  seams 
form  prominent  parts  of  the  series  of  rocks  that  underlie  the  Great 
Plains  country.  These  lignites  have  been  mined  at  a  few  localities, 
but  their  low  heating  power  and  rapid  crumbling  unfit  them  for 
general  use,  and  the  bituminous  coals  have  occupied  the  market. 
The  lignites  differ  from  the  true  coals  in  two  important  particulars : 
they  contain  a  large  amount  of  moisture  and  they  .crumble  upon 
exposure  soon  after  mining.  The  moisture  makes  them  of  low 
heating  power,  and  their  rapid  crumbling  unfits  them  for  trans- 
portation and  is  a  serious  detriment  in  burning.  An  average  analy- 
sis of  the  lignites  of  eastern  Montana  shows:  Water,  12-15;  volatile 
carbon,  40-45;  fixed  carbon,  30-35;  ash,  5-10. 

The  bituminous  coals  of  Montana  occur  in  small  isolated  fields 
within  the  mountain  region  and  in  a  great  belt  of  coal  land  that 
extends  along  the  eastern  front  of  the  Rocky  Mountains. 

The  character  of  the  coals  varies  widely  in  different  seams  and  at 

*  The  coal  beds  of  Montana  range  in  age  from  Lower  Cretaceous  to  Fort 
Union  .(Eocene,  Lower  Tertiary).  Coal  formed  in  Cretaceous  time  is  of  better 
quality  than  the  later  deposit,  but  the  Tertiary  beds  are  thicker  and  cover 
a  much  greater  area.  The  coals  are  bituminous,  sub-bituminous,  and  lignite, 
some  of  the  first  named  producing  a  fair  variety  of  coal.  It  is  estimated  that 
within  this  State  34,000  square  miles  are  underlain  by  coal  beds  more  than  2  ft. 
in  thickness. — ''Mineral  Resources,"  1910. 


134 


STEAM-BOILER  ECONOMY. 


different  fields.  Long  and  short-flamed,  coking  and  non-coking  coals 
occur  sometimes  in  adjoining  seams  of  the  same  mine.  As  a  whole 
the  coals  contain  a  high  percentage  of  ash,  and  would  not  rank  high 
in  more  favored  localities.  Some  of  the  coals,  however,  are  as  pure 
as  the  best  of  Wyoming  or  Colorado  fuels. 

The  supply  of  coal  in  the  ground  in  Montana  in  1910  is  estimated 
at  303,000,000,000  short  tons. 

Utah. — The  Green  Eiver  coal-basin  contains,  according  to  Clarence 
King's  "Geological  Exploration  of  the  40th  Parallel,"  "a  practically 
inexhaustible  supply  of  coal."  Beds  from  7  to  25  feet  thick  are  dis- 
covered at  intervals  over  500  miles,  and  from  their  ordinary  gentle 
dip  may  be  mined  with  unusual  ease.  Two  analyses  are  as  follows : 


Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Castledale  
Cedar  City  

'      3.43 
3.50 

42.81 
43  .  66 

47.81* 
43.11* 

9.73 
5.95 

*  Includes  sulphur,  which  is  very  high.      Coke  from   Cedar  City   analyzed:     Water    and 
volatile  matter,  1.42;   fixed  carbon,  76.70;  ash,  16.61;  sulphur,  5.27. 

The  areas  in  Utah  known  to  contain  workable  beds  of  coal  aggre- 
gate 13,130  square  miles.  The  coal-fields  are  important  and  widely 
distributed.  The  largest  and  commercially  most  important  region 
is  the  great  Uinta  Basin  which  lies  along  the  southern  side  of  the 
Uinta  Mountains  and  extends  to  the  southeast  as  far  as  Crested 
Butte,  Gunnison  County,  Colo. 

Washington. — The  developed  coal-fields  lie  chiefly  in  a  compara- 
tively narrow  belt,  running  nearly  due  north  and  south,  through  the 
western  portions  of  Whatcom,  Skagit,  Snohomish  and  King  counties 
into  Pierce  and  Thurston  counties.  Some  distance  to  the  east  of 
the  southern  end  of  this  belt,  in  Kittitas  County,  extensive  opera- 
tions have  been  carried  on  for  a  number  of  years.  The  main  belt 
extends  along  the  Cascade  Range,  and  important  mines  have  been 
opened  on  both  the  eastern  and  western  slopes  of  the  range.  Coal 
is  found  also  in  other  localities,  notably  in  Lincoln,  Spokane,  Cas- 
cade, and  Okanogan  counties.  The  coals  of  the  State  embrace  lignite, 
sub-bituminous  and  bituminous,  and  some  natural  coke  and  anthra- 
cite have  been  observed.  The  bituminous  coking  coals  of  Washing- 
ton are  the  only  coking  coals  on  the  Pacific  slope  of  the  United 
States.  The  coal  remaining  in  the  State  in  1910  is  estimated  at 
19,900,000,000  short  tons. 


COAL-FIELDS  OF  THE  UNITED   STATES. 


135 


ANALYSES. 


Localities. 

Moisture. 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Bellingham  Ba   .... 
Seattle 

8.39 
11  66 

33.26 
45  98 

45.59 
35  49 

12.66 
6  44 

0  43 

A  very  complete  report  on  the  coals  of  Washington  is  given  in 
Bulletin  474  of  the  U.  S.  Geological  Survey,  1911.  The  coal  of 
the  State  ranges  from  low-grade  sub-bituminous  to  anthracite.  In 
general,  anthracite  and  bituminous  coal  occur  nearer  the  axis  of 
the  Cascade  Mountains,  and  sub-bituminous  coal  farther  from  the 
range  and  nearer  the  center  of  the  Puget  Sound  depression.  The 
coal  in  Cowlitz  County  is  brownish  black  and  approaches  to  a  true 
lignite,  but  it  contains  much  less  moisture  than  the  typical  lignite 
of  North  Dakota.  The  coal  of  Kittitas  and  Pierce  counties  is  bitu- 
minous. Anthracite  is  found  in  Lewis  County,  but  it  is  not  at 
present  marketed  on  account  of  lack  of  transportation  facilities. 
The  low-grade  sub-bituminous  coal  of  Thurston,  Lewis  and 
Cowlitz  counties  crumbles  when  exposed  to  sun  and  air,  and  must 
be  used  within  a  short  time  after  it  is  brought  from  the  mine  or  it 
will  crumble  to  pieces  and  fall  through  the  grate.  From  several 
pages  of  analyses  given  in  Bulletin  474,  the  following  are  selected 
to  show  the  range  in  variation  of  the  coals  of  the  State.  Figures 
in  the  second  place  of  decimals  are  omitted. 


County. 

As  Received. 

Combustible. 

Mois- 
ture. 

Ash. 

Vol. 

F.C. 

S. 

H. 

C. 

N. 

O. 

B.T.U. 

Clallam    .  .  . 

11.2 
15.2 
14.8 
5.5 
8.2 
8.5 
3.3 
9.8 
29.1 
4.2 
2.7 
6.7 
1.9 
25.1 
22.4 

12.6 
18.9 
8.3 
21.0 
10.7 
12.1 
12.2 
69.  8f 
7.7 
34.1 
10.7 
18.5 
10.3 
8.7 
11.0 

52.5 
55.1 
43.3 
43.9 
33.5 
44.0 
40.3 
33.4 
54.9 
17.0 
8.2 
43.8 
26.5 
48.7 
50.5 

47.5 
44.9 
56.7 
56.1 
66.5 
56.0 
59.7 
66.6 
45.1 
83.0 
91.8 
56.2 
73.5 
51.3 
49  5 

6.7 
4.4* 
0.5 
0.9 
0.6 
0.6 
0.4 
1.2 
2.8 
0.8 
0.7 
0.6 
0.6 
1.2 
3.6 

6.2 

5.7 
6.0 
5.3 
5.8 
6.2 

74.4 

76.0 
80.9 
85.9 
79.0 
83.6 

1.2 

1.7 
2.2 
2.3 
1.9 
2.0 

11.5 

16.1 
9.9 
5.9 

12.8 
7.8 

13,760 

13,300 
14,720 
15,340 
14,300 
15,280 
9,790 
12,580 
14,400 
15,410 
14,210 
15,630 
12,320 
13,170 

Cowlitz  

King  

<  < 

Kittitas 

<  i 

(  t 

5.5 
4.2 
3.7 
5.7 
5.5 
5.4 
5.3 

71.7 
86.9 
91.4 
78.6 
87.9 
71.3 
73.4 

1.2 
1.4 
1.5 
2.1 
2.4 
1.4 
1.1 

18.9 
6.7 
2.7 
13.0 
3.6 
20.7 
16.6 

<  < 

<  « 
Pierce   

ti 

Thurston 

<  i 

*  In  coal  as  received. 


t  This  is  a  carbonaceous  shale,  not  a  merchantable  coal. 


136 


STEAM-BOILER  ECONOMY. 


Alaska. — The  following  information  is  condensed  from  a  report 
on  the  mining  and  mineral  wealth  of  Alaska,  by  A.  H.  Brooks,  pub- 
lished by  the  U.  S.  Geological  Survey  in  1909 : 

The  coal  fields  can  be  grouped  into  three  general  provinces — (1) 
the  Pacific  slope,  (2)  the  central  region,  and  (3)  the  northern 
region.  In  the  first  are  included,  the  lignitic  and  sub-bituminous 
coals  of  southeastern  Alaska,  Cook  Inlet,  Susitna  basin,  and  the 
Alaska  Peninsula,  as  well  as  the  high-grade  fuels  of  the  Controller 
Bay  and  Matanuska  regions.  The  central  province  includes  some 
bituminous  and  sub-bituminous  coals  on  the  lower  Yukon,  besides 
more  extensive  fields  of  lignitic  coal  in  the  upper  Yukon  basin, 
near  the  coast  line  of  Bering  Sea,  and  elsewhere.  The  northern 
region  includes  the  bituminous  and  sub-bituminous  coals  of  the  Cape 
Lisburne  region,  as  well  as  lignitic  and  sub-bituminous  coals  in  the 
Colville  basin. 

In  the  one-fifth  of  Alaska  which  has  been  geologically  surveyed, 
the  areas  of  coal-bearing  rocks  cover  12,644  square  miles,  contain- 
ing 1238  square  miles  of  known  coal  areas,  viz.,  anthracite,  30.6; 
semi-bituminous,  54.7;  bituminous,  47.2;  lignite  861  square  miles. 

The  Matanuska  coal  field  lies  about  25  miles  from  tide  water  at 
Knik  Arm,  a  northerly  embayment  of  Cook  Inlet.  The  known  com- 

ANALYSES  OF  ALASKA  COAL. 
[Compiled  from  U.  S.  Geological  Survey  reports.] 


District  and  Kind  of  Coal. 

Moisture 

Volatile 
Matter. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

ANTHRACITE. 

Bering  River,  average  of  7  analyses  

7.88 

6.15 

78.23 

7.74 

1.30 

Matanuska  River,  1  sample  . 

2.55 

7.08 

84.32 

6.05 

.57 

SEMI-BITUMINOUS. 

Bering  River,  coking,  average  of  11  analyses. 

4.76 

13.27 

74.84 

7.12 

1.51 

Matanuska  R.,  coking,  average  of  16  analyses 

2.71 

20.23 

65.39 

11.60 

.57 

BITUMINOUS. 

Lower  Yukon,  average  of  11  analyses  

4.68 

31.14 

56.62 

7.56 

.48 

SUB-BITUMINOUS. 

Matanuska  River,  average  of  4  analyses  
Alaska  Peninsula,  average  of  5  analyses  

6.56 
2.34 

35.43 

38.68 

49.44 
49.75 

8.57 
9.22 

.37 
1.07 

Cape  Lisburne,  average  of  11  analyses  

9.35 

38.01 

47.19 

5.45 

.35 

LIGNITE. 

Port  Graham,  1  sample  

16.87 

37.48 

39.12 

6.53 

.39 

Southeastern  Alaska,  average  of  5  samples  .  .  . 

1.97 

37.84 

35.18 

24.23 

.57 

Colville  River,  1  sample  

1J.50 

30.33 

30.27 

27.90 

.50 

Upper  Yukon,  Canadian,  aver,  of  13  analyses. 

13.08 

39.88 

39.28 

7.72 

1.26 

Seward  Peninsula,  1  sample  

24  92 

38   15 

33  58 

3  35 

68 

Kachemak  Bav,  average  of  6  analyses.    . 

19  85 

40  48 

30  99 

8  68 

35 

Unga  Island,  average  ot  2  analyses  

10.92 

53.36 

28.25 

7^47 

1^36 

Tyonek,  average  of  4  analyses 

8  35 

54.20 

30  92 

6  53 

.38 

Chistochina  River,  1  sample  

15.91 

60.35 

19.46 

4^28 

COAL-FIELDS  OF  THE  UNITED  STATES. 


137 


mercially  valuable  coals  of  the  field  vary  from  sub-bituminous  to  semi- 
bituminous,  with  some  anthracite.  The  beds  vary  from  5  to  36  feet 
in  thickness,  and  the  total  area  known  to  be  underlain  by  coal  is  46J 
square  miles.  The  total  area  of  what  may  prove  to  be  coal-bearing 
rocks  is  approximately  900  square  miles.  Up  to  the  present  time  there 
has  been  no  means  of  transporting  this  coal  to-market,  so  that  no 
mining  has  been  done,  but  many  beds  have  been  opened  in  pros- 
pecting. [A  railroad  is  about  to  be  built  to  this  field  by  the  Govern- 
ment. 1915.] 

LIGNITES  AND  LIGNITIC  COALS  OF  THE  WESTERN  STATES.* 
Lignite  is  the  next  stage  above  peat  in  the  formation  of  coal.  It 
varies  greatly  both  in  appearance  and  in  chemical  composition.  Its 
color  ranges  from  light  yellow  to  deep  brown  or  black.  The  lignites 
belong  to  a  later  geologic  period  than  the  Carboniferous.  They 
occur  principally  in  Cretaceous  and  Tertiary  formations.  The  beds, 
which  are  often  of  great  thickness,  present  the  same  general  charac- 
teristics as  those  of  the  true  coals.  Many  instances  occur  in  which 
portions  of  beds  of  lignite  have  changed  to  bituminous  and  even  to 
anthracite.  The  lignites  of  Western  America  resemble  the  "brown 
coals"  of  Europe  in  holding  a  large  amount  of  water,  the  percentage 
in  most  of  them  being  from  12  to  15,  though  some  have  as  low  as  4 
and  others  as  high  as  20  per  cent.  The  percentage  of  ash  is  usually 
low,  from  2  to  9  per  cent,  while  the  sulphur  is  generally  below  1  per 
cent.  The  following  analyses  are  given  by  Dr.  R.  W.  Raymond  in 
Trans.  A.  I.  M.  E.,  vol.  ii.,  1873 : 


C. 

H. 

N. 

0. 

s. 

Mois- 
ture. 

Ash. 

Monte  Diablo,  Cal  
Weber  Canon,  Utah  
Echo  Canon,  Utah  

Carbon  Station,  Wyo.  .  . 

i  (            u           « 

Coos  Bay,  Oregon  
Alaska 

59.72 
64.84 
69.84 
64.99 
69.14 
56.24 
55  79 

5.08 
4.34 
3.90 
3.76 
4.36 
3.38 
3.26 

1.01 
1.29 
1.93 
1.74 
1.25 
0.42 
0.61 

15.69 
15.52 
10.99 
15.20 
9.54 
21.82 
19.01 

3.92 
1.60 
0.77 
1.07 
1.03 
0.81 
0.63 

8.94 
9.41 
9.17 
11.56 
8.06 
13.28 
16.52 

5.64 
3.00 
3.40 
1.68 
6.62 
4.05 
4.18 

<  < 

67.67 

4.66 

1.58 

12.80 

0.92 

3.08 

9.28 

Canon  City  Colo 

67  58 

7  42 

13  42 

0  63 

5  18 

5  77 

Baker  Co.,  Ore  

60.72 

4.30 

14.42 

2.08 

14.68 

3.80 

Texas. — According   to    Bulletin    No.    189    of   the   University   of 
Texas  the  lignite  fields  probably  extend  over  60,000   square   miles 

*  Including  the  sub-bituminous  coals  of  the  classification  of  the  U.  S.  Geol. 
Survey. 


138 


STEAM-BOILER  ECONOMY. 


and  contain  a  supply  in  excess  of  30,000,000,000  tons.  Every  known 
variety  of  lignite  is  found  from  a  material  carrying  but  a  few  per 
cent  of  fixed  carbon  to  nearly  45  per  cent,  and  with  from  30  per 
cent  volatile  matter  to  more  than  76  'per  cent.  Physically  the 
lignites  range  from  what  is  but  little  more  than  carbonized  wood 
to  a  material  almost  like  bituminous  coal.  In  thickness,  the  beds 
run  to  15  feet  or  more,  and  they  are  found  from  the  surface  to 
depths  of  400  to  600  feet.  In  a  general  way  lignite  is  found  in  all 
that  part  of  Texas  lying  west  of  long.  97°  W.  and  north  of 
lat.  31°  N.,  but  there  are  important  areas  outside  of  these  boun- 
daries/ The  following  analyses  show  the  extreme  range  of  compo- 
sition and  the  average  of  fifteen  mine  samples : 


B.T.U. 

B.T.U. 

Mois- 
ture. 

Vol. 

F.C. 

Ash. 

s. 

C. 

H. 

0. 

N. 

per  Ib. 

as 

per  Ib. 
Com- 

mined. 

bustible. 

Milam  Co  

29.1 

29.0 

24.5 

17.6 

3.3 

38.7 

2.7 

7.3 

1.4 

7439 

13,900 

Hopkins  Co.  .  .  . 

33.9 

45.9 

3.4 

16.8 

0.7 

34.1 

2.3 

11.1 

1.1 

6474 

13,130 

Av.  of  15  

33.0 

40.4 

17.2 

9.0 

1.1 

40.1 

3.0 

12.3 

1.2 

7614 

13,310 

Another  series  of  23  samples  received  from  mining  companies 
gave  moisture  7.3  to  37.3,  av.  25.2;  volatile  matter  20.3  to  45.6, 
av.  37.6;  fixed  carbon  21.1  to  38.9,  av.  28.5;  ash  4.8  to  6.1,  av. 
8.8.  B.  T.  U.  per  Ib.  as  received  6291  to  10;411,  av.  7661  B.  T.  U. 
per  Ib. 

In  his  report  on  brown  coal  and  lignite  '(Greol.  Survey  of  Texas, 
1892)  Mr.  E.  T.  Dumble  gives  the  ultimate  analysis  of  22  brown 
coals,  dried  at  221°  F.  The  average  figures  are,  C,  60.98;  H, 
4.01;  0,  22.16;  N,  1.48;  ash,  11.01.  Water  in  the  freshly  mined 
coal  8.55  to  18.25,  av.  13.67. 

Arizona, — Several  beds  of  lignitic  coal  of  extremely  variable 
composition  have  been  found  in  the  Territory.  Two  analyses  of 
coals  from  Deer  Creek,  Ariz.,  taken  from  locations  8  miles  apart 
are  given  below.  The  first  is  a  semi-bituminous  coal;  the  second, 
a  lignite: 


Volatile  combustible  matter  and  water 14 . 5 

Fixed  carbon 61.0 

Ash..  24.5 


II. 

47.6 

44.0 

8.4 


COAL-FIELDS  OF   THE    UNITED^  STATES.  139 

Although  Arizona  has  not  produced  any  coal  on  a  commercial 
scale,  there  are  fields  of  much  promise  which  may  be  profitably 
exploited  when  transportation  is  afforded  and  when  population  and 
manufactures  have  reached  a  point  which  will  provide  a  market 
for  the  output. — Mineral  Resources,  1910. 

Idaho. — There  are  several  areas  in  Idaho  in  which  lignite  beds 
are  found,  but  little  mining  has  been  done.  The  production,  which 
was  6508  tons  in  1907,  declined  to  4448  tons  in  1910. 

North  Dakota. — The  coal  of  North  Dakota  is  a  lignite  of  inferior 
quality  and  does  not  compare  favorably  with  that  brought  from 
other  localities.  The  output  is  restricted  to  local  markets.  It  has 
been  found  well  adapted  for  brick-burning  on  account  of  its  smoke- 
less quality. 

Nevada. — A  bed  of  coal,  5  to  6  feet  thick,  20  miles  east  of 
Eureka,  is  mined  for  local  consumption. 

California. — The  Mt.  Diablo  coal-field  contains  several  beds,  which 
vary  greatly  in  thickness.  The  coal  is  of  rather  inferior  quality. 
Coal  has  been  found  in  many  portions  of  the  State,  but  the  beds  are 
mostly  small  in  extent  and  the  quality  poor.  Nearly  all  of  the  coal 
of  California  is  lignite,  that  from  Monterey  County  alone  being 
classed  as  bituminous.  San  Francisco  is  dependent  for  its  coal  supply 
chiefly  on  coals  brought  by  water  from  other  States  and  from  foreign 
countries.  An  analysis  of  Mt.  Diablo  coal  is  as  follows: 

Moisture 14.69 

Volatile  matter 33.89 

Fixed  carbon 46 . 84 

Ash 4.58 

At  various  times,  within  the  last  ten  years,  efforts  have  been 
made  to  exploit  the  California  fields,  but  they  have  not  been  success- 
ful.—"Mineral  Kesources,"  1910. 

Oregon. — The  developments  are  confined  to  the  coal-basin  in 
Coos  County,  though  other  lignite  discoveries  have  been  reported. 
The  field  covers  several  hundred  square  miles  of  territory,  stretching 
from  the  coast  15  or  20  miles  inland.  The  coals  are  true  lignites, 
very  high  in  water  and  volatile  matter. 


140 


STEAM-BOILER  ECONOMY. 

OREGON   LIGNITES. 


Moisture. 

Vol.  Mat. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Coos  Bay 

15  45 

41   55 

34  95 

8  05 

2  53 

17  27 

44.15 

32  40 

6  18 

1  37 

Yaquina  Bay      .    . 

13  03 

46  20 

32  60 

7.10 

I  07 

John  Day  River  .... 

t  (           a 

4.55 
6.54 

40.00 
34.45 

48.19 
52.41 

7.26 
5.95 

.60 
.65 

CHAPTER  V. 

TESTS  OF  THE  HEATING  VALUE    OF  AMERICAN  AND  FOREIGN 

COALS. 

Johnson's  Tests  of  American  Coals. — The  results  of  the  tests  of 
American  coals  made  by  Prof.  Walter  R.  Johnson  for  the  United 
States  Navy  Department  in  1842  and  1843,  the  report  of  which 
was  published  in  a  government  document  covering  600  pages,  are 
of  little  use  in  determining  the  relative  value  of  American  coals 
when  burned  under  the  conditions  of  modern  practice.  The  boiler 
used  by  Johnson  was  of  the  two-flue  type,  set  only  9  to  10  inches 
from  the  grate-bars,  the  furnace  being  entirely  unsuited  for  bitu- 
minous coal.  Some  of  the  anthracites  were  burned  with  an  ex- 
cessive air-supply,  causing  them  to  give  results  much  below  those 
that  may  be  obtained  under  favorable  conditions. 

Scheurer-Kestner's  Tests  of  European  Coals. — A  series  of  tests 
of  European  coals  was  made  by  Scheurer-Kestner  and  Meunier- 
Dollfus  in  1868,  and  the  results  were  reported  in  the  Bulletin  de  la 
Societ'e  Industrielle  de  Mulhouse.  An  excellent  study  of  these  tests, 
with  others,  is  that  by  M.  L.  Gruner  in  his  papers  on  "The  Classi- 
fication and  Heating  Power  of  Coals,"  translated  from  the  French 
by  R.  P.  Rothwell,  and  published  in  the  Engineering  and  Mining 
Journal,  July  18th,  1874,  et  seq.* 

Mahler's  Tests  of  European  Coals. — MM.  Scheurer-Kestner  and 
Meunier-Dollfus  found  that  the  heating  power  as  determined  by 
the  Favre  and  Silbermann  calorimeter  was  notably  higher  than  that 
calculated  from  the  analysis  by  means  of  the  Dulong  formula.  More 
recently  numerous  determinations,  by  different  American  chemists,  of 
the  heating  values  of  various  American  coals,  by  means  of  the  Thomp- 

*  Considerable  space  was  given  in  the  first  edition  of  this  book  to  the  dis- 
cussion of  Johnson's  and  Scheurer-Kestner's  tests.  They  are  now  considered 
unimportant,  in  view  of  more  recent  tests.  A  critical  review  of  these  tests  was 
published  by  the  author  in  The  Engineering  and  Mining  Journal  in  October, 
1891. 

141 


142  STEAM-BOILER  ECONOMY. 

son  calorimeter  or  its  modifications,  showed,  apparently,  that  the  heat- 
ing values  of  these  coals  were  much  less  than  those  calculated  from  the 
analyses.  The  contradictory  results  of  all  these  researches  must  now 
be  set  aside  in  view  of  the  work  of  Mahler,  in  France,  published  in 
1892,  supplemented  by  the  more  recent  work  of  Lord  and  Haas  in  this 
country  and  by  that  of  Bunte  in  Germany,  all  of  whom  agree  in  show- 
ing that  the  calorimetric  values  and  those  calculated  by  the  Dulong 
formula  from  the  ultimate  .analysis  are  nearly  identical,  except  in  the 
case  of  cannel-coal,  lignite,  turf,  and  wood,  which  by  Mahler's  tests 
show  a  calorimetric  value  ranging  from  2  to  12  per  cent  higher  than 
that  calculated  from  the  analysis. 

Mahler's  research  was  made  under  the  auspices  of  the  Societe 
d'Encouragement  pour  1'Industrie  Rationale,  with  its  financial  assist- 
ance to  the  extent  of  3000  francs,  and  his  report  is  published  as  a 
pamphlet  extract  from  the  Bulletin  of  the  Societe,  of  1892,  occupying 
73  pages  quarto,  with  two  large  plates.  It  is  entitled  "Contribution 
a  1'Etude  des  Combustibles;  Determination  Industrielle  de  leur  Puis- 
sance Calorifique,  par  P.  Mahler,  Ingenieur  Civil  des  Mines,"  etc. 

The  calorimeter  used  by  Mahler  was  a  modified  form  of  the 
"calorimetric  bomb"  of  MM.  Berthelot  and  Vielle,  described  in  the 
Annales  de  Physique  et  de  Chimie  in  1881  and  1885.  The  bomb, 
with  its  auxiliary  apparatus,  is  shown  in  the  cut,  Fig.  7,  on  page  145. 
It  is  described  in  detail  by  the  report,  and  the  description  of  a  similar 
bomb,  used  by  Professors  Slosson  and  Colburn  in  their  investigations 
of  Wyoming  coals,  with  the  method  of  operating  it,  is  given  below. 

Mahler's  results  are  shown  in  condensed  form  in  the  table  on  the 
opposite  page. 

Mahler's  formula  gives  the  same  result  as  his  modification  of 
Dulong's  when  0  +  N  =  3.29%,  and  higher  results  when  0  +  N  is 
greater  than  3.29%,  but  the  difference  is  small,  less  than  1%,  until 
0  -|-  N  becomes  greater  than  10%.  The  average  results  for  the  several 
classes  of  coals  calculated  by  the  Mahler  formula  are  greater  or  less 
than  the  calorimetric  results,  as  follows :  Anthracite  and  anthracitic, 
+  19;  fat  and  semi-fat,— 34;  fat  gas-coals,  +117;  flaming  coals, 
lignitic,  +  42 ;  average  of  these  four  classes,  +  26,  as  compared  with 
—18,  the  average  difference  between  the  results  calculated  by  the 
modified  Dulong  formula  and  the  calorimetric  result,  as  shown  in  the 
table.  For  the  lignites,  turf,  and  wood,  Mahler's  formula  gives  much 
smaller  differences  than  Dulong's,  viz.:  +102,  +6,  -f  194,  —294, 
+  119,  +  134,  +  64,  as  compared  with  —157,  —299,  —138,  —  734, 


TESTS  OF  TEE  HEATING    VALUE  OF  COALS. 


143 


HEATING  POWER   OF   COALS.     (P.   MAHLER.) 


1 

2 
3 
4 
5 
6 
7 
8 

9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 

20 
21 

23 
21 
25 
26 

27 
28 
29 
30 
31 

82 
33 
34 

35 

36 
37 

38 

Kind  of  Coal. 

Coal  Dry  and  Free  from  Ash. 

||| 

Composition. 

Heating  power 
Calories. 

C. 

H. 

O  +  N 

"5 

31 

•2 

ANTHRACITE  AND  ANTHRACITIC. 
'  Pennsylvania 

97.00 

M.» 

94.  8U 
96.81 
94.00 
93.28 
89.56 

95.37 
95.24 
92.86 
93.46 
91.49 
90.00 
91.46 
9'2  39 

2.20 
1.50 
2.16 
3.07 
3.12 
3.17 
3.95 
3.78 

2.43 
3.26 
4.99 
3.48 
5  39 
6.83 
4.59 
3.83 

8256 
8216 
8121 
8532 

8456 
8203 
8540 

8687 

8462 
8173 
8130 
8528 
8333 
8169 
8653 
8704 

4-  206 
-  43 
4-  9 

-  123 
-  34 
4-  113 

4-  17 

4-  18 

4-  95 
4-  61 
-  116 
-  175 
-f  77 
-  119 
—  34 
-  80 
-  110 
-  61 
-  285 

-  66 

-  14 
-  44 
—  49 

-  191 
4-  165 
4-  211 

4-  286 

-  199 
-  79 
+  24 
-  11 

-  102 

-  74 
-  18 

-  157 
-  299 
-  138 

-  734 

-  400 
-  396 
-  583 

De  la  Mure  (Grand  Couche)  

Hay-Duong  (Tonkiu)  .   .. 

Kebao 

Commeiitry  '                          .... 

Blanzy,  Puits  Ste.-Barbe  

Grande-Combe,  Puits  Petassas 

Crt'usot. 

Average  

FAT  AND  SEMI-FAT  (DEMI-GRASSB). 
Demi-grasse,  d'Anzin,  Fosse  St.  Marc.    .  .  . 
Grande  Combe  ....          .... 

85.92 
86.62 
86.00 
88.07 

78.49 
76.77 
80.50 
78.25 

77  15 

91.26 
91.19 
90.11 
90.10 
89.20 
88.89 
90.03 
87.84 
89.53 
89.23 
86.52 

4.27 

4.46 
4.38 
4.40 
4.67 

4.84 
4  80 
4.87 
4.84 
5.03 
4.84 

4.48 
4.35 
5.51 
5.49 
6.14 
6.27 
5.17 
7.30 
5.63 
5.74 
8.64 

8656 
8756 
8767 
8834 
8574 
8797 
8839 
8G39 
8867 
8857 
8667 

8751 
8817 
8651 
8659 
8651 
8678 
8805 
8559 
8757 
8796 
8382 

Roche-la-Moliere.  

Grasse  Anzin  great  vein 

Ronchamp  .... 

Lens               .                   .... 

Saint  Etienne 

79.16 
80  71 

FAT  GAS-COALS. 
Bethune  ....             . 

69.59 
69.20 
67.98 
65.73 
60.04 
68.36 
47.00 

87.03 
87.26 
85.39 
84.52 
85.06 
88.57 
83.79 

5.37 
5.44 

5.58 
5.54 
5.60 
5.72 
6.57 

7.60 
7.30 
9.13 
9.94 
8.73 
5.72 
9.63 

8668 
^749 

8573 
8598 
8408 
8768 
8431 

8654 
8705 
8524 
8407 
8573 
8979 
8717 

Lens  

Firminy.  

Montrambert 

Coinmentry  
Wigan,  Lancashire  

Cannel-coal,  Niddrie  

Average.. 

FLAMING  COALS,  LIGNITIC. 
Montoic     ...                              . 

6°  93 

83.95 
84.26 

as.  17 

81.54 

78.72 

5.64 
5.27 
5.68 
5.64 
5.67 

10  42 
10.46 
11.14 
12.83 
15.61 

8570 
8350 
8270 
8083 
7837 

8371 

8294 
8072 
7735 

Blanzy  (.Puits  Ste.-Marie)  

68.  Of> 
64.20 
60.61 

58.77 

Decazeville  (Bourran) 

Blanzy  (Puits  Ste.-Eug6nie.  

Decazeville  (Tramont)    ... 

Average 

Average  of  above  four  classes 

LIGNITES. 
Terre  de  Feu  

47.23 
49.66 
50.05 

31.07 

71.01 
69.24 
66.36 

57.21 

51.08 
50.44 
44.44 

5.94 
5.06 
5.01 

5.96 

6.02 

5.88 
6.17 

23.05 
25.71 
28.63 

36.82 

42.90 
43.69 
49.39 

7039 
6616 
6076 

5903 

4828 
4689 
4200 

6882 
6317 
5938 

5169 

4428 
4293 
3617 

Trifail  (Styria) 

Vaurigard  

TURF  FROM  BOHEMIA  

WOOD. 
Partially  d  ry,  Sapin  de  Norvege  

Bois  de  ChSne  de  Lorraine 

Cellulose,  C12H10*O10  

..   .. 

*  Dulong's  formula,  slightly  modified  by  Mahler,  is:  Q  =^  [8140C  +  34,500 (H  - 

It  may  be  put  under  the  form  Q-^  [8140C  +  34,500H  -  4312(O4N  -I)]. 
Mahler's  own  formula  is  Q  =  TJD  [8140C  4  34,500H  -  3000(O  +  N)]. 


144  STEAM-BOILER  ECONOMY. 

-400,  —396,  —583,  the  figures  in  the  table.  For  all  ordinary  coals, 
therefore,  Dulong's  formula  may  be  considered  the  more  accurate  of 
the  two,  giving  an  average  difference  of  only  18  calories*  in  over  8000. 

DESCRIPTION  OF  MAHLER'S  BOMB  CALORIMETER.! 

The  essential  conditions  for  the  determination  of  heat  of  combus- 
tion are  that  the  product  be  completely  burned,  that  the  heat  pass 
entirely  into  the  water  of  the  calorimeter  vessel,  and  that  the  combus- 
tion be  as  quick  as  possible.  These  conditions  are  best  attained  by  the 
process  devised  by  Berthelot,  according  to  which  the  combustion  takes 
place  in  a  closed  steel  vessel  (the  so-called  bomb)  filled  with  oxygen 
under  twenty  to  twenty-five  atmospheres  pressure  and  almost  entirely 
immersed  in  the  water  of  the  calorimeter.  Under  these  circumstances 
a  hydrocarbon  burns  completely  to  carbon  dioxide  and  water  in  a  few 
seconds,  none  of  the  products  of  combustion  can  escape  and  the  heat 
passes  into  the  surrounding  water  in  the  course  of  two  or  three 
minutes.  The  high  price  of  Berthelot's  calorimeter,  about  $1500,  has 
prevented  it  from  coming  into  common  use.  In  June,  1892,  an 
account  was  published  of  a  modifica^n  of  Berthelot's  apparatus  in- 
vented by  M.  Mahler  in  which  the  expensive  platinum  lining  of  the 
bomb  was  replaced  by  a  thin  coating  of  enamel  without  impairing  the 
efficiency  of  the  instrument.  A  calorimeter  of  this  kind  was  pro- 
cured by  the  University  of  Wyoming  in  July,  1894,  for  the  study  of 
the  coal  and  petroleum  of  the  State  and  for  use  in  food  investigations 
in  the  Agricultural  Experiment  Station. 

The  bomb  (B  in  cut)  of  our  apparatus  is  15  cm.  high  and  10  cm. 
in  diameter,  with  an  average  thickness  of  8  mm.  It  is  Martin- Sie- 
mens soft-forged  steel  of  a  resistance  of  50  kilogs.  per  sq.  mm.  of 
section  (about  70,000  Ibs.  per  sq.  in.),  and  20%  elongation.  It  is 
nickel-plated  on  the  outside  and  coated  on  the  inside  with  a  thin  white 
enamel  to  prevent  corrosion  by  the  oxygen  and  the  acids  which  are 
among  the  products  of  combustion.  The  capacity  of  the  bomb  is 
580  cc.  A  platinum  tray  ((7),  of  30  mm.  in  diameter  and  5  mm.  in 

*  A  calorie  is  the  amount  of  heat  required  to  raise  1  kilogram  of  water  1  ° 
centigrade,  =3.968  B.T.U.  When  used  as  a  measure  of  the  heating  value  of  a 
fuel  it  is  the  number  of  units  of  weight  of  water  which  may  be  heated  1°  C. 
by  the  combustion  of  1  unit  of  weight  of  the  fuel.  The  unit  of  weight  may 
be  either  a  gram,  a  kilogram  or  a  pound.  When  thus  used  a  calorie  is  equiv- 
alent to  1.8  British  thermal  units. 

f  From  an  article  on  "The  Heating  Power  of  Wyoming  Coal  and  Oil,"  by 
Professors  E.  E.  Slosson  and  L.  C.  Colburn,  published  in  a  special  Bulletin  of  the 
University  of  Wyoming,  Laramie,  Wyo.,  January,  1895.  Another  description 
will  be  found  in  Mahler's  paper  on  "The  Calorific  Power  of  Combustibles"  (Bul- 
letin de  la  Socie"te*  d' Encouragement  pour  Tlndustrie  Nationale,  Paris,  1892),  and 
in  Poole's  'Calorific  Power  of  Fuels"  (John  Wiley  &  Sons,  New  York,  1898). 


TESTS   OF  THE  HEATING  VALUE  OF  COALS. 


145 


depth,  is  suspended  from  the  cover  by  a  rod  of  platinum.  A  similar 
rod  passing  through  the  cover,  but  insulated  from  it,  reaches  nearly 
to  the  tray  and  serves  as  the  other  electrode.  The  cover  is  screwed  on 
over  the  top  of  the  bomb  and  a  hermetical  joint  secured  by  a  ring  of 
lead.  The  oxygen  is  passed  in  through  the  stem  of  the  needle- valve, 
which  is  screwed  down  when  the  bomb  is  filled.  The  bomb  is  set  in  a 
support  which  touches  the  bottom  of  the  calorimeter  vessel  on  three 
points.  The  calorimeter  vessel  is  a  pail  of  thin  brass,  23  cm.  high  and 


FIG.  7. — MAHLER'S  BOMB  CALORIMETER. 

A,  water- -acket;  B,  bomb  of  enameled  steel;  C,  platinum  tray;  D,  calorimeter- 
vessel;  E,  electrode;  F,  iron  wire  for  ignition;  G,  support  for  stirring- 
apparatus;  K,  stirring-mechanism;  L,  lever  for  stirring;  M,  manometer; 
O,  cylinder  of  oxygen;  S,  stirring-apparatus;  T,  thermometer;  7,  clamp. 

14  cm.  diameter.  This  rests  on  three  points  of  a  light  wooden  support, 
and  is  surrounded  by  a  large  double-walled  vessel,  covered  with  thick 
felt,  containing  water  at  the  normal  temperature  of  the  room.  An 
ingenious  stirring  mechanism  enables  one  to  keep  the  water  of  the 
calorimeter  in  thermal  equilibrium  with  slight  effort.  The  calorimeter 
is  so  well  isolated  from  external  influences  that  the  water  often  does 
not  vary  in  temperature  .01°  in  fifteen  minutes,  although  the  air  of 
the  room  may  be  quite  variable. 

Two  thermometers  were  used,  one  reading  between  8°  and  18°  C., 
and  the  other  between  18°  and  28° ;  each  degree  covering  a  space  of 
3^  cm.  They  are  graduated  to  ^°,  an(^  were  rea^  to  0.01°,  although 
with  a  glass  they  can  be  read  to  a  much  finer  interval. 


146  STEAM-BOILER  ECONOMY. 

The  oxygen  used  was  made  in  the  laboratory,  purified  by  passing 
through  a  solution  of  caustic  potash  and  three  rolls  of  copper  gauze, 
and  kept  in  gas-bags ;  the  slight  correction  indicated  for  Berthelot  for 
the  loss  of  heat  through  vaporization  of  water  has  not  been  applied. 


THE  PROCESS  OF  COMBUSTION. 

One  gram  of  the  coal  or  oil  is  weighed  into  the  tared  platinum 
tray,  which  is  then  attached  to  the  platinum  rod  in  the  calorimeter- 
bomb.  A  piece  of  iron  wire  of  known  weight  is  stretched  across  from 
the  rod  supporting  the  tray  to  the  insulated  support,  and  preferably 
touching  the  combustible  or  buried  in  it.  The  bomb  is  then  placed  in 
a  lead-lined  clamp,  and  the  top  tightly  screwed  on  by  means  of  a 
wrench.  The  needle-valve  is  opened  and  connected  with  the  com- 
pression pump  by  a  long  slender  copper  tube.  Oxygen  is  then  forced 
into  the  bomb  until  the  manometer  reads  20  or  25  atmospheres.  The 
needle-valve  is  closed  and  disconnected  from  the  filling  tube,  and  the 
bomb  is  immersed  in  the  water  of  the  calorimeter.  The  water  should 
be  2°  to  3°  lower  in  temperature  than  the  air  of  the  room  and  the 
water  in  the  jacket  of  the  calorimeter,  and  a  sufficient  amount  should 
be  weighed  out  to  cover  the  bomb  nearly  to  the  top  of  the  insulated 
electrode.  In  our  instrument  2309  grams  of  water  was  usually  taken, 
as  that  gave  with  the  water  value  of  the  apparatus  (491  grams)  a 
convenient  factor  for  calculation.  The  stirring  apparatus  is  kept  in 
motion,  and,  as  soon  as  the  change  in  temperature  becomes  constant, 
readings  of  the  thermometer  are  taken  at  intervals  of  one  minute.  At 
the  end  of  the  fifth  minute  the  combustible  is  fired  by  passing  an  elec- 
tric current  through  the  iron  wire,  raising  it  to  redness.  We  used  a 
plunge  battery  of  six  bichromate  cells  for  this  purpose.  One  wire  is 
connected  to  the  insulated  electrode,  and  the  other  is  touched  to  some 
exposed  part  of  the  bomb.  In  about  ten  seconds  the  thermometer  is 
observed  to  rise,  rapidly  at  first,  then  more  slowly,  reaching  a  maxi- 
mum usually  on  the  second  or  third  minute  after  firing.  After  the 
maximum  it  falls  regularly  and  slowly  if  the  proper  temperature  has 
been  chosen  for  the  water,  and  readings  are  again  made  at  intervals  of 
a  minute  for  five  minutes  more.  Then  the  bomb  is  taken  out  of  the 
calorimeter,  the  needle-valve  cautionsly  opened  to  allow  the  products 
of  combustion  and  residual  oxygen  to  escape ;  after  which  the  bomb  is 
opened  and  rinsed  out  with  distilled  water.  The  rinsings  are  titrated 
with  a  standard  solution  of  potassium  hydrate  or  sodium  carbonate  to 
determine  the  amount  of  nitric  acid  formed  by  the  combustion ;  and, 
if  the  combustible  contains  sulphur,  the  solution  is  set  aside  for 
determination  of  sulphuric  acid.  The  whole  operation,  including  the 
weighing  of  the  sample  and  pumping  in  the  oxygen,  can  be  completed 
in  less  than  an  hour  if  everything  works  well. 

Multiplying  the  weight  of  water  taken  plus  the  water  value  of  the 
apparatus  by  the  corrected  rise  in  temperature  gives  the  heat  of 


TESTS  OF   THE  HEATING  VALUE  OF  COALS.  147 

combustion  of  one  gram  of  the  substance,  subject  to  the  corrections 
mentioned  below. 

CORRECTIONS. 

1.  Correction  for  the  Influence  of  the  Temperature  of  the  Environ- 
ment. —  This  is  the  largest  and  most  important  correction  to  be  made, 
although  on  acount  of  the  short  interval  during  which  the  tempera- 
ture rises  —  usually  two  minutes  —  it  is  smaller  in  this  process  than  in 
any  other. 

As  there  is  no  way  of  measuring  directly  the  amount  of  heat  lost 
or  gained  by  the  calorimeter  from  the  moment  of  firing  to  the  moment 
when  all  the  heat  of  combustion  has  been  given  up  to  the  water  sur- 
rounding the  bomb,  it  is  necessary  to  calculate  this  from  the  rate  of 
change  of  temperature  before  firing  and  the  rate  of  change  when  the 
temperature  has  come  again  to  equilibrium.  This  correction  is  most 
accurately  given  by  the  application  of  the  E-egnauld-Pfaundler  for- 
mula. If  the  preliminary  period  and  the  final  period  are  each  five 
minutes,  with  readings  of  the  thermometer  every  minute,  the  correc- 
tion according  to  this  formula  is  : 


-  (N  -  5)tM}-          +  (N  - 


where  t  indicates  the  temperature  at  the  end  of  the  minute  designated 
by  the  subscript;  t5  is  the  instinct  of  firing;  N  is  the  number  of  the 
maximum  reading  ;  tM  is  the  average  of  the  five  readings  before 
firing;  T  is  the  average  of  the  readings  of  the  final  period;  D  is  the 
average  change  in  temperature  during  the  final  period,  and  d  is  the 
average  change  in  temperature  during  the  preliminary  period. 

As  in  practice  the  maximum  temperature  nearly  always  occurs  on 
the  seventh,  the  eighth,  or  the  ninth  minute,  the  formula  can  be 
reduced  for  these  three  cases  to  the  following  forms,  which  are  easy 
to  calculate  : 

When  the  maximum  is  the  end  of  the  seventh  minute  the  correc- 
tion for  the  loss  or  gain  of  heat  during  the  minutes  5-6  and  6-7  is 


1  f  [(2<6  +  ti)  -  (2tp  +  *5)][(fr  +  ts)  -  (to  +  ti2)]    ,    ,.         , 

5  r       «i2  +  w  -  ft,  +  fc)  ~'s) 

When  the  maximum  is  the  eighth  minute  the  loss  or  gain  for  the 
minutes  5-6,  6-7,  7-8  is 


2*7  +  ts)    ~  (3*Q  +  fe)][(*8  +  te)    ~   (*13    +  to)] 

fe  +  ts)  -  do  +  W  ' 


148  STEAM-BOILER  ECONOMY. 

When  the  maximum  is  the  ninth  minute  the  loss  or  gain  for  the 
minutes  5-6,  6-7,  7-8,  8-9  is 


f  [(2  . 


This  correction  becomes  a  minimum  when  the  temperature  before 
firing  is  rising  about  three  times  as  fast  as  it  falls  after  the  maximum. 

As  the  period  of  combustion  is  so  short,  M.  Mahler  has  given  a 
method  of  correction  based  on  Newton's  law  which  gives  results 
sufficiently  exact  for  technical  work.  His  rules  are  : 

1.  The  law  of  decrease  of  temperature  observed  after  the  maxi- 
mum represents  the  loss  of  heat  before  the  maximum  and  for  any 
given  minute,  on  condition  that  the  mean  temperature  of  this  minute 
does  not  differ  more  than  one  degree  from  the  maximum  temperature. 

II.  If  the  temperature  of  the  given  minute  differs  by  more  than 
one  degree  but  less  than  two  degrees  from  that  of  the  maximum,  the 
number  that  represents  the  law  of  decrease  at  the  moment  of  the 
maximum  less  0.005  will  give  the  desired  correction. 

A  comparison  of  the  two  methods  in  some  twenty  cases  showed  an 
average  difference  of  0.0013,  which  on  one  gram  naphthalene  would 
amount  to  about  three  calories,  or  0.03  per  cent;  a  difference  within 
the  limit  of  error  in  technical  work. 

2.  Correction  for  Formation  of  Nitric  Acid.  —  About  fifty  milli- 
grams of  nitric  acid  are  formed  from  the  nitrogen  of  the  air  by  the 
combustion,  and  it  is  necessary  to  ascertain  the  amount  of  this  and 
subtract  the  heat  of  formation,  227  cal.  per  gram,  from  the  heat  of 
combustion  of  the  substance  under  examination.     This  is  estimated 
by  titration  with  a  standard  alkali  solution  containing  3.706  grams  of 
sodium  carbonate,  Na2C03.     One  cubic  centimeter  of  this  solution  is 
equal  to  .0044  gram  nitric  acid,  of  which  the  heat  of  formation  is  one 
calorie,  so  the  number  of  cubic  centimeters  required  to  titrate  the 
washings  of  the  bomb  can  be  written  at  once  as  calories.     Methyl 
orange  is  used  as  an  indicator. 

3.  Correction  for  the  Combustion  of  the  Iron  Wire.  —  The  combus- 
tion of  the  small  piece  of  iron  wire  used  to  ignite  the  combustible 
adds  to  the  apparent  rise  in  temperature,  and  correction  must  be  made 
by  taking  a  known  weight  of  wire  and  subtracting  its  heat  of  combus- 
tion.   A  No.  32  to  36,  Brown  and  Sharpe  gauge,  is  suitable,  and  it  is 
preferable  to  use   the   copper-plated  wire,   as  the  plain   wire   easily 
becomes  oxidized  on  the  surface.     Of  No.  36  wire  one  meter  weighs 
.3160  gram;  of  this  in  our  experiments  we  used  a  length  of  4.8  centi- 
meters, giving  a  heat  of  combustion  of  25  calories. 

The  heat  of  combustion  of  iron  under  these  circumstances  is  stated 
to  be  1650  cal.  per  gram.*  This  is  on  the  assumption  that  all  the 
iron  is  burned  to  Fe304.  That  this  is  not  correct  is  shown  by  the 

*  Berthelot:  Traite"  Pratique  de  Calorimetrie  Chimique,  p.  139. 


TESTS  OF  THE  HEATING  VALUE  OF  COALS.  149 

following  analysis  of  the  iron  oxide  resulting  from  some  twenty  com- 
bustions each:  No.  1,  71.59  per  cent  iron  in  oxide;  No".  2,  75.81  per 
cent  iron  in  oxide.  The  first  would  correspond  to  74.7  per  cent 
Fe304  and  25.3  per  cent  Fe203,  while  the  second  might  be  composed 
of  86.8  per  cent  Fe304  and  13.2  per  cent  unburned  iron.  Other 
mixtures  of  iron  and  its  oxides  would  of  course  give  the  same  analyt- 
ical results.  The  heat  of  combustion  of  ferric  oxide  is  not  exactly 
known,  but  it  is  certainly  less  than  that  of  Fe304.  It  appears  from 
this  that  the  character  of  the  oxides  formed  is  variable  and  the  ordi- 
nary correction  consequently  inaccurate  by  several  calories.  The  error 
is  not,  however,  as  great  as  the  analysis  would  seem  to  indicate,  for  it 
was  only  the  larger  particles  such  as  could  be  easily  picked  off  that 
were  taken  for  analysis. 

4.  Correction  for  Sulphur. — The  presence  of  sulphur  in  the  com- 
bustible necessitates  another  correction,  for  the  free  sulphuric  acid 
formed  by  the  combustion  of  sulphur  compounds  will  be  titrated  as 
nitric  although  its  heat  of  combustion  is  different  and  the  heat  of  the 
burning  sulphur  is  a  legitimate  part  of  the  heat  of  combustion  of  the 
fuel.  The  sulphuric  acid  must  therefore  be  determined  in  the  rins- 
ings of  the  bomb  after  the  titration  for  free  acid,  and  the  heat  of  for- 
mation of  its  equivalent  in  nitric  acid  subtracted  from  the  number 
obtained  by  titration.  The  weight  of  barium  sulphate  multiplied  by 
100  gives  directly  the  number  of  calories  to  be  subtracted. 

Sulphur,  however,  exists  in  coal  in  three  forms:  organic  sulphur 
compounds,  pyrites,  and  sulphates,  chiefly  gypsum.  Of  these  the 
third  at  least  would  not  be  converted  into  free  acid  by  the  combustion, 
and  the  ordinary  correction  would  be  too  great.  The  point  is  of 
especial  importance  in  dealing  with  Wyoming  coals,  for,  although  the 
percentage  of  sulphur  is  generally  small,  yet  it  is  more  often  in  the 
form  of  gypsum  than  pyrites.  Nevertheless,  as  to  find  the  original 
state  of  the  sulphur  would  require  two  analyses,  the  whole  is  regarded 
as  forming  sulphuric  acid,  and  the  equivalent,  usually  amounting  to 
about  5  cal.,  has  been  subtracted  in  all  cases. 

DETERMINATION    OF    WATER    VALUE    OF    THE    APPARATUS. 

The  heat  produced  by  combustion  is  absorbed  not  only  by  the 
water  in  the  calorimeter,  but  also  by  the  calorimeter  vessel,  the  bomb, 
the  stirring  apparatus  and  thermometer  in  contact  with  it.  But  the 
amount  of  heat  absorbed  by  them  depends  on  their  weight  and 
material.  It  is  therefore  necessary  to  find  the  water  value  of  the 
apparatus,  that  is,  what  weight  of  water  would  absorb  the  same 
amount  of  heat  for  the  same. rise  in  temperature.  This  is  done  by 
multiplying  the  weight  of  the  different  parts  of  the  apparatus  by  the 
specific^  heat  of  the  material  of  which  they  are  composed.*  In  this 
case  the  calculation  was  as  follows: 

*  The  weight  of  the  enamel  on  the  bomb  was  not  known.  The  water  value 
of  the  apparatus  as  calculated  is  therefore  too  low. 


150 


STEAM-BOILER  ECONOMY. 


Calorimeter  vessel  445  g.,  stirring  apparatus  143  g.,  588  g. 

brass  X  .093    54.69 

Bomb,  3920  g.  steel  X  .1097 430.03 

22.36  g.  platinum  X  .0324 72 

8  g.  lead  X  .031 25 

Thermometer,  bulb  2.72  g.,  tube  33.56  g.,  J  immersed,  8.61 

g.  glass  X  .184   1.58 

35.36  g.  mercury  X  .033 ' 1.17 

Oxygen,  (20  atmospheres  pressure)  16.7  X  155  * 2.59 

Water  value 491.03 

Another  method  of  determining  the  water  value  of  a  calorimeter 
is  to  burn  in  it  certain  compounds  whose  heat  of  combustion  is  accu- 
rately known.  This  has  the  advantage  that  the  water  value  of  the 
whole  apparatus  is  determined  directly  and  under  the  same  condi- 
tions as  in  an  ordinary  combustion,  but  it  has  the  disadvantage  that 
the  heat  of  combustion  of  no  compound  is  exactly  known.  In  deter- 
mining the  water  value  of  our  calorimeter  we  made  twelve  combus- 
tions with  resublimed  naphthalene,  of  which  the  heat  of  combustion 
as  determined  by  Berthelot  and  his  assistants  is  9692  calories.  The 
average  of  the  twelve  combustions  gave  491.4  grams  as  the  water  value 
of  the  calorimeter.  One  combustion  with  granulated  sugar,  using  2 
gm.  and  taking  the  heat  of  combustion  as  3961.7  cal.  per  gram,  gave 
491  g.  as  the  value.  As  all  these  are  in  satisfactory  agreement,  the 
number  491  has  been  adopted  as  the  water  value.  A  difference  of  one 
gram  in  water  value  makes  a  difference  of  about  .03  per  cent  in  the 
final  result. 

An  Example. — The  method  of  calculating  the  heat  of  combustion 
may  be  made  more  clear  by  giving  in  detail  an  example  in  which  the 
corrections  are  ususally  large. 

Coal  No.  33.     L.  R.  Meyer,  Carbon.     November  30,  1894. 
1  gram  coal.     .0250  g.  wire.     2300  g.  water  in  calorimeter. 


Preliminary  Period. 

Combustion  Period. 

Final  Period. 

0—11.47°  C. 
1—11.47 
3—11.48 
4—11.48 
5—11.48  Fired. 

5—11.48°  C. 
5i—  12.50 
6—13.34 
7—13.63 
8—13.64 
9—13.64 

9—  13.64°  C. 
10—13.63 
11—13.62 
12—13.62 
13—13.62 
14—13.61 

Nitric  acid  =  9.0  cc.     Sodium  carbonate  solution  =9   cal.     Weight  BaSO4, 
.0472. 


*  Specific  heat  at  constant  volume. 


TESTS  OF  THE  HEATING  VALUE  OF  COALS.  151 

From  the  9th  to  the  14th  reading  .03°  heat  was  lost,  or  .006°  per 
minute.  Then  for  the  three  and  a  half  minutes,  5^-6,  6-7,  7-8,  8-9, 
the  total  loss  =  .021°.  The  temperature  rose  .01°  during  the  pre- 
liminary period,  or  .002°  per  minute.  The  correction  for  the  half- 
minute  5-5|  is  therefore  .001.  The  total  rise  in  temperature  is  from 
11.48°  to  13.64°,  or  2.16° ;  adding  to  this  the  correction  .02°  gives 
2.18°  for  the  true  rise  due  to  combustion.  The  water  value  of  the 
apparatus,  491  g.,  added  to  the  weight  of  water  used,  2300  g.,  gives 
2791  g.,  which  multiplied  by  2.18  gives  6084.4  calories.  The  weight 
of  the  barium  sulphate  with  the  decimal  point  moved  two  places  to  the 
right  gives  4.7  to  be  subtracted  from  9.0  cal.,  leaving  4.3  cal.  The 
weight  of  the  wire,  .0250  g.,  multiplied  by  1650  gives  41.2  cal.  The 
sum  of  the  corrections  for  formation  of  iron  oxide  and  nitric  acid, 
45.5,  subtracted  from  6084.4  gives  6039  calories  for  the  true  heat  of 
the  combustion  of  one  gram  of  the  coal.  The  use  of  Regnault's 
formula  in  this  case  would  make  the  rise  of  temperature  2.179°  and 
the  heat  of  combustion  6036  cal. 


NOTES    ON    CALORIMETRY. 

The  use  of  a  cylinder  of  oxygen  under  great  pressure,  such  as  is 
now  in  the  market,  dispenses  with  a  compression-pump,  and  shortens 
the  time  required  for  a  combustion  by  one-half.  It  has- the  disadvan- 
tage that  the  quality  of  the  oxygen  is  not  as  much  under  control  as 
where  it  is  made  in  the  laboratory. 

It  is  not  necessary  that  the  coal  should  be  finely  powdered,  nor  is 
there  any  difficulty  in  using  fine  samples.  Of  the  samples  used,  one 
was  in  coarse  fragments  and  some  had  been  passed  through  a  hun- 
dred-mesh sieve.  In  using  very  fine  coal  or  freshly  sublimed  naphtha- 
lene, it  is  convenient  to  compress  it  into  tablets  with  a  "diamond  mor- 
tar" such  as  is  used  in  crushing  minerals  for  analysis. 

The  cylinder  of  the  compression  pump  must  be  kept  cool  by  a 
water-jacket,  or  the  oil  will  become  ignited  by  the  compressed  oxygen 
and  an  explosion  result. 

The  rapidity  with  which  the  heat  is  given  up  to  the  water  of  the 
calorimeter  is  shown  by  the  following  average  of  ten  determinations : 

Heat  given  off  during  the  period  5  -5|  =  27.9  per  cent. 
"     "        "        "        "      5*-6   =  50.3   "      " 

u  «      «  «          u          ((        Q   _y    _    20   1    "        ' ' 

K        «     «        n       K       ti     7  _g   _     17"      ' ' 


100.0 


That  is,  78.2  per  cent  of  the  total  heat  is  absorbed  by  the  water  dur- 
ing the  first  minute  and  98.3  per  cent  during  the  first  two  minutes. 

Care  must  be  taken  to  scrape  off  the  iron  oxide  from  the  electrodes 
before  attaching  the  new  wire,  as  a  very  thin  film  will  prevent  ignition 
by  the  electric  current. 


152  STEAM-BOILER  ECONOMY. 

A  third  method  of  standardizing  the  calorimeter  is  used  by  the 
chemists  of  the  U.  S.  Geological  Survey  (Bull.  415,  1910,  p.  242). 
We  quote  .  .  .  third,  by  adding  a  definite  amount  of  warm  water 
at  known  temperature  to  a  definite  amount  of  water  at  some 
known  lower  temperature  in  the  calorimeter  and  noting  the  result- 
ing temperature.  From  these  data  the  actual  heat  equivalent  can 
be  calculated.  The  determination  by  each  method  is  duplicated 
until  satisfactory  averages  are  obtained  and  a  mean  of  these  averages 
insures  a  figure  for  the  water  equivalent  of  the  apparatus  which 
is  very  near  the  truth. 

The  __  thermometer  readings  are  made  through  a  telescope  at 
some  distance  from  the  calorimeter,  so  as  to  avoid  errors  due  to 
radiation  of  heat  from  the  body  of  the  operator. 

Determinations  of  the  heating  value  of  coal  are  always  made 
in  duplicate  and  almost  invariably  agree  to  within  50  British  thermal 
units,  or  about  one-third  of  1  per  cent.  The  practice  of  reporting 
heat  values  to  the  decimal  or  even  to  the  final  whole  number  as- 
sumes an  extreme  accuracy  which  the  determination  does  not  war- 
rant. It  would  be  far  better  and  would  not  affect  values  if  the 
British  thermal  units  were  reported  to  the  nearest  ten. 

The  Parr  Calorimeter.  A  calorimeter  invented  by  Prof.  S.  W. 
Parr,  which  is  often  used  in  commercial  work  and  is  less  expensive 
than  the  Mahler,  is  shown  in  Fig.  8. 

The  can  AA  for  the  water  has  a  capacity  of  2  liters.  The  insulating 
vessels  BB  and  CC  are  of  indurated  fiber.  A  charge  of  coal  and  chem- 
ical is  put  in  the  cartridge  D.  Upon  ignition,  the  heat  generated  is 
imparted  to  the  water  and  the  rise  in  temperature  is  indicated  on 
the  finely  graduated  thermometer  T.  The  cartridge  or  bomb  rests  on 
the  pivot  F  and  is  made  to  revolve,  and  by  aid  of  the  small  turbine 
wings  attached  effects  a  complete  circulation  of  the  water  and  equal- 
ization of  temperature. 

The  oxygen  required  for  combustion  is  supplied  by  sodium  perox- 
ide. The  reaction  accompanying  the  combustion  may  be  represented 
by  the  equation: 

56Na2O2+C25H,8O3=25Na2C03  +  ISNaOH   +  22^0 

Sod.  perox.        Coal  Sod.  carb.          Sod.  hydrate      Sod.  oxide 

"With  certain  substances  such  as  coke,  anthracites,  petroleums,  etc., 
a  more  vigorously  oxidizing  medium  is  needed  than  exists  in  the 
sodium  peroxide  alone,  such  as  a  mixture  of  potassium  chlorate  and 
nitrate  in  the  proportion  of  1  to  4  and  this  mixture  used  in  the 
ratio  of  1  to  10  of  the  sodium  peroxide. 


TESTS  OF  THE  HEATING  VALUE  OF  COALS. 


153 


Further  extension  of  the  use  of  the  instrument  to  other  types 
of  coal  and  to  petroleum  has  made  it  necessary  to  extend  still  fur- 
ther the  oxidizing  power  of  the  chemicals  employed  beyond  what 
is  afforded  by  the  chlorate  mixture.  In 
addition  to  this  the  use  of  the  residue 
for  determining  the  total  carbon  and  sul- 
phur has  made  it  highly  desirable  in 
such  additional  chemicals  to  avoid  the 
use  of  compounds  containing  carbons  or 
sulphur.  To  meet  these  conditions,  the 
so-called  "boro-mixture"  has  been  devised. 
For  the  addition  the  following  mixture 
has  also  been  used:  Boric  acid,  11  parts; 
potassium  chlorate,  4  parts;  magnesium 
powder,  1  part.  The  correction  factor  of 
the  mixture  is  found  by  trial  with  a  pure 
chemical  of  known  heat  value,  such  as 
naphthalene  or  by  burning  with  a  coal 
whose  heat  value  is  already  accurately 
known. 

Lord  and  Haas's  Tests  of  American 
Coals,— In  1897  Professors  N".  W.  Lord 
and  F.  Haas,  of  the  Ohio  State  Uni- 
versity, Columbus,  0.,  presented  a  paper 
to  the  American  Institute  of  Mining  Engineers  (Trans.,  vol. 
xxvii.  p.  259)  giving  the  results  of  proximate  and  ultimate 
analyses  and  determinations  of  calorific  value,  by  means  of  the 
Mahler  calorimeter,  of  forty  different  samples  of  coal,  selected 
from  seven  different  mining  regions.  Prof.  Lord  also  published  a 
paper  in  Engineering  News  of  February  16,  1899,  giving  the  results 
of  similar  tests  of  five  samples  of  coal  from  different  parts  of  Jackson 
Co.,  Ohio.  The  figures  obtained  in  both  series  of  tests  are  given  in 
the  table  on  pages  156  and  157.  The  figures  in  the  last  two  columns 
have  been  calculated  by  the  author,  to  show  the  heating  value  and  the 
per  cent  of  fixed  carbon  of  the  combustible,  which  were  not  given  in 
the  original  papers.  The  ultimate  analyses  as  reported  include  the 
hydrogen  and  oxygen  of  the  moisture  together  with  that  of  the  dry 
coal,  and  the  figures  for  "average,  dry  coal,"  have  been  computed  by 
the  author-  in  order  to  make  the  analyses  comparable  with  analyses  of 
other  coals. 


FIG.  8. — THE  PARR  CALORIM- 
ETER. 


154  STEAM-BOILER  ECONOMY. 

The  extreme  accuracy  of  these  tests  is  shown  by  the  close  agree- 
ment of  the  results  with  those  obtained  by  Mahler  with  foreign 
coals  of  similar  composition,  as  well  as  by  the  correspondence  of 
the  calorimetric  determinations  with  the  heating  value  as  calculated 
by  the  Dulong  formula.  The  student  is  referred  to  the  original 
paper  for  a  detailed  statement  of  the  precautions  taken  to  insure 
accurate  work  with  the  calorimeter. 

The  following  is  quoted  from  the  paper : 

"The  probable  error  of  a  single  calorimeter  determination  from 
the  mean  result  of  a  large  number  was  computed  from  all  the  re- 
sults on  21  samples  of  coal,  on  each  of  which  more  than  one  deter- 
mination was  made.  There  were  50  separate  results  on  the  21  samples. 
Computing  the  error  by  the  ordinary  formula  gave  plus  or  minus 
20  units,  or  about  0.3  of  1  per  cent  as  the  probable  error  of  one 
determination.  These  results  were  obtained  by  different  observers 
and  at  considerable  intervals  of  time,  and  include  slight  possible 
variations  in  the  condition  of  the  sample  as  to  moisture  and  oxida- 
tion. Duplicate  results  obtained  at  the  same  time  by  the  same 
observer  frequently  gave  much  closer  checks. 

"One  gram  of  the  coal  was  dried  at  100°  to  105°  C.  for  one  hour 
in  a  crucible,  the  loss  being  called  moisture.  After  drying,  the  same 
portion  was  heated  3J  minutes  over  a  Bunsen  burner,  then  3^  min- 
utes over  a  blast-lamp,  and  the  loss  was  called  volatile  combustible.  The 
crucible  was  tightly  covered  and  not  allowed  to  cool  during  the  change 
from  burner  to  blast-lamp. 

"  The  results  of  the  work  are  given  in  the  following  tables,  in 
which  the  coals  of  each  seam  are  grouped  together.  In  addition  to  the 
analytical  and  calorimetric  data  the  following  figures  are  tabulated : 

"  1.  The  calorimetric  power,  computed  from  Dulong's  formula,  in 
this  form: 

Cal.  power  =  8080C  +  34,462  (H  -  |O)  +  2250S, 

C,  H,  0,  and  S  being  the  amounts  of  carbon,  hydrogen,  oxygen,  and 
sulphur  in  one  unit  of  the  coal. 

"  2.  The  difference  between  this  result  and  the  bomb  determina- 
tion, expressed  in  percentages. 

"  On  examining  the  accompanying  table  of  results,  the  following 
points  appear : 

"  In  the  first  place,  the  remarkable  coincidence  between  the  heat- 
ing powers,  as  calculated  from  Dulong's  formula,  and  the  experi- 
mental determinations.  In  the  case  of  the  averages  of  the  different 
seams  we  find  practical  identity  between  the  heating  power  as  calcu- 
lated from  the  formula  based  simply  on  the  heat  developed  by  the 
combustible  elements,  and  the  result  of  the  calorimeter.  This  is  so 


TESTS  OF  THE  HEATING  VALUE  OF  COALS,  155 

much  at  variance  with  the  claims  of  many  writers  that,  were  it  not 
the  result  of  so  many  determinations,  it  might  pass  as  a  mere  accident. 
The  maximum  difference  between  the  heat  calculated  from  the  ele- 
mentary analysis  and  the  heat  developed  in  the  bomb  is  2  per  cent 
of  the  total  calculated  heat,  the  minimum  difference  0.1  per  cent. 
The  possible  error  of  an  ultimate  analysis  may  be  placed  at  0.5  per 
cent  on  carbon  and  0.2  per  cent  on  hydrogen,  especially  with  coals  as 
high  in  ash  and  sulphur  as  are  many  of  the  samples  included  in  our 
tests.  This  would  lead  to  an  ejror  of  about  108  units,  or  nearly  1.4 
per  cent  on  the  calculated  heat  value.  While,  of  course,  the  probable 
error  of  the  ultimate  analysis  is  less  than  this,  it  seams  certainly 
possible  that  the  differences  between  the  observed  and  calculated  heat 
values  are  within  the  limits  of  experiment. 

"  Attempts  to  derive  a  general  law  for  all  the  coals  examined  were 
abandoned,  and  the  question  was  taken  up,  how  far  the  coal  of  a  given 
deposit  or  seam  can  be  regarded  as  of  uniform  quality,  and  its  specific 
character  determined.  This  has  led  to  the  interesting  results  given 
in  the  tables.  Taking  the  coals  of  the  same  seam,  we  averaged  the 
results  of  the  calorimeter,  and,  reducing  by  the  average  ash  and  moist- 
ure, soon  found  that  comparable  results  were  obtained  by  regarding 
this  value  as  a  constant  for  the  seam  over  the  area  examined." 

"  The  results  of  our  tests  seem  to  indicate  the  interesting  conclu- 
sion that  the  character  of  a  coal-seam,  as  far  as  its  fuel  value  is  con- 
cerned, is  a  nearly  constant  quantity  over  considerable  areas.  The 
determination  of  the  value  for  seams  would  be  of  great  use,  as  the 
rapid  proximate  analysis,  or,  for  that  matter,  merely  the  determina- 
tion of  ash  and  moisture,  in  low-sulphur  coals,  would  be  sufficient  to 
grade  coals  of  the  same  vein.  Of  course  it  is  dangerous  to  argue  from 
so  few  examples;  but  the  proposition  seems  reasonable.  At  least,  we 
hope  that  further  work  may  confirm  these  conclusions, 

Prof.  Lord  says  concerning  the  Jackson  Co.,  Ohio,  coals: 

"  The  failure  of  the  last  two  samples  to  show  close  correspondence 
between  the  calculated  values  by  Dulong's  formula  and  the  calori- 
metric  results  is  contrary  to  our  experience  with  other  coals.  These 
last  two  analyses  are  the  average  of  duplicates,  which  do  not  agree  very 
satisfactorily,  and  therefore  the  results  are  open  to  question,  as  I  fear 
some  carbon  may  have  escaped  combustion.  The  other  analyses  are 
the  averages  of  very  closely  agreeing  duplicates.  If  the  conclusion 
as  to  the  comparative  constancy  of  the  heating  value  of  the  combus- 
tible in  any  given  seam  is  correct,  then  the  determination  of  the  heat- 
ing power  of  any  particular  sample  from  the  seam  becomes  a  simple 
matter,  if  the  ash,  sulphur,  and  moisture  in  the  sample  be  known,  and 
the  seam  constant  for  the  kind  of  fuel  be  known." 

In  an  article  on  "The  Heating  Value  of  Coal,"  published  by  the 
author  in  Vol.  1  of  "Mineral  Industry,"  1892,  p.  97,  Mahler's  tests 


156 


STEAM-BOILER  ECONOMY. 


TABLE  OF  RESULTS.     LORD  AND  HAAS'S  TESTS. 


POCAHONTAS  COAL   (SEMI-BITUMINOUS). 


Coal  Diy 

£ 

5-S 

*i 

and  Free 

• 

—   CO 

from 

i 

3 

yjj 

8 

Asb. 

z 

<» 

t.  — 

CD 

Location  of  Mine. 

e 

§ 

M 

is- 

(^ 

g 

Carbon. 

Hydrogen. 

Oxygen. 

a 

3 

"a. 
1 

i 

Moisture. 

Volatile  Coi 

1 
1 

£ 

Calorimeter 

Calorific  Po 
lated  from 

Difference. 

O 

Calorimeter 
Value. 

Hun  of  mine  

83  75 

•1  °? 

3  36 

R5 

57 

7  25 

80 

18  30 

7Q   ft* 

8062 

8089 

g 

80  10 

a~«« 

60 

8  60 

75 

17  05  ?a  fin 

7915 

8l!l9  fl7*1 

41         o 

85.46 

4.25 

3.24 

.85 

.57 

5.63 

.63 

18.62 

75.12 

8185 

8246 

-    .6 

80.14 

8732 

fiS 

6  99 

61 

17   92,74   48 

8080 

80  61 

8745 

"         *•     

85.40 

4.39 

3.94 

.85 

.62 

4.80 

.85 

18.60 

75.75 

8281 

8258 

+  -3 

80.29 

8777 

60 

6  65 

73 

18  10 

74  *>2 

8105 

80  48 

8751 

80.18 

Average  1-3-5.  
"  Dry  Coal. 

84.87 
85.52 

4.29 
4.24 

3.51 
2.85 

.85 
.86 

.59 
.59 

5.89 
5.94 

.76 

18.51 

74.84 

8176 

8198 



8759 

THACKER  COAL,   WEST  VIRGINIA. 


78.90 

5.14 

6.88 

1.42 

1.16 

1.18 
1.81 
1.40 

6  50 
7.50 
7.30 
6.05 

1.40 
1.60 
1.18 
1.35 

35.0057.10 
34.7556.15 
36.07,55.45 
36.3556.25 

7768 
7738 
7711 
7867 

7876 

-,.8 

62.00 
61  77 

8434 
8513 

tk        "    2d  lot   .... 

Nut  Coal  

7831 

+'.4 

60.59 
60.75 

8425 
8496 

"      "   2d  lot        .... 

78.40 

5.19 

7.56 

1.40 

1.39 

1~28 
1.30 

6.84 

1.88 

35.54|56.24 

7771 

7817 

7853 

61.28 
61.38 

8467 
8465 

5~17 
5.09 

~*2 
6.07 

1.41 
1.43 

Average  11-14  

78.65 
79.75 

6.27 
6.36 

1.38 

35.6856.67 

"       "Dry  Coal. 

PITTSBURGH  COAL,    ALLEGHENY  CO.,    PENNSYLVANIA. 


77.20 
76.56 
76.57 
73.50 

5.26 
5.22 
5.13 

T  19 

8.51 
7.00 
8.82 
8.08 
8.02 
8.89 
8.39 

.68 
.67 
.64 
.44 
.60 
.23 
.37 

1.42 
1.60 
1.76 
2  54 
1.80 

liee 

5.93 
7.95 
6.08 
9.25 
8.86 
9.05 
9.05 

.45 

.08 
.07 
.08 
.09 
2.10 
1.75 

36.42 
34.38 
37.79 
37.67 
88.91 
36.20 
36.20 

56.20 
36.59 
55.06 
5-2.00 
31.14 
32.  (55 
53.00 

7691 
T630 
7765 
7396 
7496 
7354 
7394 

!rr,r 

7719 
7614 
7436 
75  ->8 
7404 
,7433 

-  .3 
-1.2 
+2.0 
—  «5 
-  .4 

-  '.5 

60.68 
62.14 
59.30 
57.99 
56.79 
59.26 
59.42 

8304 

8378 
8352 
8248 
8324 
8277 
8299 

8313 

Turtle  Creek  .... 

Carnegie.....  

74.45 
73.91 
74.48 

5.27 
5.15 
5.05 

N.  Mansfield  
Turtle  Creek        

Average  

75.24 
76.30 

5.18 
5.10 

8.24 
7.12 

1.51 
1.53 

1.79 
1.82 

8.02 
8.13 

1.37 

36.80 

53.81 

7532 

17550 



59.39 

"       Dry  Coal.... 

MIDDLE  KITTANNING  (DARLINGTON  COAL),   LAWRENCE  CO.,   PENNSYLVANIA. 


77.83 
74.  CO 
77  93 
76.81 

72.78 
7°  8° 

5  22 
5.06 
5.17 
5.22 
4.93 
5  25 
5.14 

9.38 
8.23 
7.95 
8.52 
10.57 
8.55 
10.14 

1.65 
1.40 
.65 
.62 
.34 
.38 
.24 

1.57 
1.96 
2.35 
1.18 
1.68 
3.25 
1.86 

4.35 
8.75 
4.95 
6.65 
8.70 
8.80 
8.05 

1.60 
1.50 
0.75 
0.70 
2.70 
2.85 
2.55 

36.40 
34.33 
38.53 
36.80 
35.10 
37  50 
35.60 

36.32 

57.65 
55.42 
55.77 
55.85 
53.50 
-0.85 
53.80 

7785 
7360 
78-J5 
7638 
7245 
7304 
7300 

7719 
7460 
7787 
7663 
7173 
7395 
7320 

Ios  ecio  eco  w  eo 

+7  -f  i+7  i 

61.308278 
61  .75  8201 
50.148-J56 

60.28  8244 
60.38  8177 
57.56  8267 
60.188166 

Beaver  Creek.  .  .  . 

Wampum  
Near  Wampum  
Hoytdale  

Clinton                         .  . 

73.57 

Average  • 
"       Dry  Coal.. 

75.19 
76.58 

5.14 
5.03 

9.05 
7.57 

1.46 
1,49 

1.98 
2.02 

7.18 
7.31 

1.81 

54.69 

7494 

7502 



60.09 

8226 

TESTS  OF  THE  HEATING    VALUE  OF  COALS. 


157 


TABLE  OF  RESULTS.     LORD  AND  HAAS'S  TESTS.— Continued. 


UPPER   FREEPORT   COAL,    OHIO  AND   PENNSYLVANIA. 


Coal  Dry 

•4£ 

4J 

and  Free 

.u 

?.$ 

C 

from 

i 

3 

3 

i 

31 

i. 

Ash. 

Location  of  Mine. 

s 

.a 

c 

£ 

J,u 

ft 

s 

1 

a 

t 

a 
p 

1 

w 

% 

4 

oisture. 

£ 

0 

xed  Carb( 

ilorimeter 

lo  rifle  PCM 
ated  fron 

fference. 

| 

6 
1 

llorimeter 
Value. 

O 

W 

O 

fc 

CO 

< 

E 

> 

fe 

S 

0 

Q 

s 

0 

East  Palestine,  O. 

70.58 

4.88 

7.76 

.24 

3.65 

11.891 

0.82 

34.98 

52.65 

7109 

7132 

-    .3 

60.08 

8113 

78.23 

5.15 

8.82 

.47 

1.75   9.58! 

1.6537.45 

51.32 

7380 

735'? 

-   .3 

57.81 

8^7 

Waterford,  O  .  .  .  . 

74.89 

5.15    7.80 

.4(1 

3.44    7.82 

1.5537.29 

58  34 

745P 

7529 

—     9 

58.85 

8?so 

Yellow  Creek,  O.. 
Steubenville,  O... 

73.15 
74.73 

4.98    7.41 
5.26    8.06 

.40 
.44 

3.89   9  17 
2.85!  7.66 

1.2338.72 
1.4789.23 

50.88 
51  54 

7464 
7504 

7393 
7567 

I1-? 

56.79 

56.78 

8330 
R°rt7 

70.61 
71.40 

5.1910.33 
4.62  10.68 

.44 
.20 

3.01 
3.00 

9.42 
9.10 

2.4337.79 
2.40  39.20 

50.36 
49  30 

7088 
7113 

7116 
6970 

57.13 
55.71 

8041 

S037 

Steubeuville,  O  

+2.0 

Salineville,  O  

72  6-2 

5.13    9.92 

°S 

3  00 

S    1(1 

2  80  36  30 

5°  80 

7271 

7276 

j 

59  26 

81fiO 

Palestine,  O  

71.29 

5.00    9.28 

.34 

2.6410.45 

2J5  36170 

50,70 

7277 

7136 

+2.0 

58.01 

8339 

New  Galilee,  Pa  

73  57 

5.20    8.94 

RT 

2  24   8  70 

2  30  36  70 

5°  30 

7267 

7401 

1  8 

58  76 

SI  65 

Palestine  O         •  . 

73  64 

5  06    9  47 

24 

2  34   8  25 

2  45  sfl  r.n 

52  70 

7344 

7'440 

RQ    «Q 

Average        .... 

72  65 

5  06    R  QK 

SI 

0  80 

9  10 

1  93  s1?  91 

51  63 

7293 

7292 

ft  107 

Dry  Coal.... 

74.09 

4.94 

7.87 

.37 

2.95 

9.28 

MAHONING   COAL. 


Salineville,  O  
Dry  Coal. 

71.13 
73.44 

4  95   9.93 
4.75    7.36 

1.23 

1.27 

1.86 
1.92 

10.90 
11.26 

3.15 

35.00 

50.95 

7032 

7068 

-   .5 

59.28 

8182 

JACKSON   CO  ,   OHIO. 


Center. 
North.. 
South.. 

West.. 
East  . . . 


Dry  Coal, 


71.205 


Average 70.72  5.47 


71. 
70. 

71.425.37 
70.79 


.125. 


70.055.4317.091.49 
.50  17.71 
4916. 
19. 


.96  1 


.50 

.43  0  64 
5.5518.601.460.95 


.491 


17.971.4 


1.84 

1.450.76 
1.45 


77.004.9711.66:1.60 


1.13 


4.10 

8.26 

35.15 

52.49 

6854 

6835 

-0.3 

59.897821 

3.38 

8.55 

34.09 

54.09 

693? 

6R90 

-0.7 

61.35 

7868 

4.48 

7.02 

37.66 

50.82 

6956 

(i860 

-1.3 

57.42 

7860 

1.65 

8.65 

34.30 

55.40 

6981 

6795 

-2.7 

61.76 

7783 

2.65 

8.50 

37.75 

51.10 

7069 

6854 

-3.1 

57.51 

7946 

3.25 

8.17 

35.79 

52.78 

6953 

6847 

59.59 

7856 

3.54 

MIDDLE  KITTANKING   (HOCKING   VALLEY  COAL),    OHIO. 


Lump        

69.42 

5.35 

16.27 

1.46 

1.67 
1.63 
1.67 
1.50 
1.43 

5.83 
10.10 
9.67 
10.53 
8.50 

6.72 
6.45 
6.65 
6.34 
6.40 

37.13 
36.60 
34.14 
35.18 
36.05 

50.32 
46.85 
49.54 
47.95 
49.05 

6882 
6603 
6496 
6482 
6610 

6790 
6520 

^ 

57.54 
56.14 
59.20 
57.68 
57.64 

7870 
7913 
7762 
7797 
7767 

44     2d  sample 

66.50 

5.16 

15.57 

1.43 

Lump,  3d  sample  

68.18 

5.36 

15.09 

1.44 

6740 

-1.9 

Average  

1.58 

1.59 
1.70 

8.93 

8.00 
8.57 

6.51 

35.82 

48.74 

6612 
6663 

..   . 



58.12 
58J6 

7822 

Average  6-8-10  
"Dry  Coal. 

68.03 
72.84 

5^29 

4.88 

15.64 
10.47 

1.44 
1.54 

6.59 

35.77 

49.64 

6683 

7800 

158 


STEAM-BOILER  ECONOMY. 


were  reviewed,  and  a  curve  was  drawn  showing  the  relation  of  the 
heating  value  per  pound  of  combustible  to  the  percentage  of  fixed 
carbon  in  the  combustible.  In  a  discussion  of  the  paper  of  Professors 
Lord  and  Haas,  in  1897  (Trans.  A.  I.  M.  E.,  vol.  xxvii,  p.  946),  the 
same  curve  was  presented  together  with  plottings  of  the  results  of 
Lord  and  Haas,  the  results  of  tests  of  13  coals  by  C.  W.  Houghton, 
M.  E.,  in  1896,  with  a  Carpenter  calorimeter,  the  figures  of  which 
are  given  below,  and  the  average  results  of  tests  of  coals  from  four 
counties  in  Wyoming  (see  table  on  p.  160).  The  curve  and  plottings 
are  reproduced  on  page  159.  It  appears  that  all  of  Mahler's  tests  of 
coals  containing  between  60  and  97  per  cent  of  fixed  carbon  in  the 
combustible  (one  cannel-coal  excepted)  are  enclosed  in  a  narrow  field 
surrounding  the  curve,  but  that  with  coals  lower  in  fixed  carbon  the 
field  widens  out  and  the  curve  drops  rapidly.  The  Pocahontas  coals 
tested  by  Lord  and  Haas  come  close  to  the  Mahler  curve,  and  the  aver- 
age results  of  their  tests  of  coals  that  are  high  in  volatile  matter  and 
low  in  fixed  carbon  all  fall  within  the  Mahler  field,  except  the  Jackson 
Co.  Ohio  coal,  which  is  slightly  below  it.  Houghton's  tests  cover  the 
breadth  of  the  field  and  extend  slightly  above  and  below  it,  while 
the  Wyoming  coals  are  all  below  it.  The  Mahler  curve  is  plotted  from 
the  figures  given  in  the  table  on  page  143. 

The  results  of  Mr.  Houghton's  tests  are  as  follows: 


Fixed 

Heating 

'  Value. 

Carbon. 
Per  Cent. 

Calories. 

B.T.U.perlb. 

1    Youghiogheny  Pa  

62.6 

8330 

14,990 

2    Pittsburgh  Pa          

60.6 

7890 

14,200 

3    Vanderpool  Ky          

61.5 

8000 

14,400 

4    Brier  Hill  O              

61.8 

7890 

14,200 

5    Hocking  Valley  O        

57.5 

7830 

14,090 

6    Big  Muddy  111               

62.5 

8080 

14,540 

7    Streator  111                     

56.2 

7890 

14,200 

8   Ladd   111                           

56.8 

8170 

14,710 

9    Seatonville  111            

54.7 

8060 

14,510 

10    Wilmington  111             

57.1 

7840 

14,210 

11    Mt  Olive  111                  

57.1 

7610 

13,700 

^2    Indiana  block                    

61.4 

7950 

14,310 

jg    Indiana  lump                    

55.6 

7670 

13,810 

Coal  Dry  and  Free  from  Ash. 


Lord  and  Haas's  tests  cover  only  a  small  portion  of  the  range  of 
composition  of  the  coals  tested  by  Mahler.    Mahler's  tests,  excluding 


TESTS  OF  THE  HEATING  VALUE  OF  COALS. 


159 


160 


STEAM-BOILER  ECONOMY. 


the  lignites,  cover  the  entire  range  between  58  and  97  per  cent  of 
fixed  carbon,  while  Lord  and  Haas's  are  confined  between  55.7  and 
62.2  per  cent,  except  the  five  tests  of  Pocahontas  coal,  which  are  be- 
tween 80.1  and  81.2  per  cent.  Excluding  the  coals  that  have  below 
58  per  cent  of  fixed  carbon  in  the  combustible,  the  variation  of  any 
one  of  Lord  and  Haas's  coals  from  the  Mahler  line  does  not  exceed 
320  calories,  or  4  per  cent.  Taking  the  average  figure  for  each  class 
of  coals,  it  falls  in  all  cases  within  the  limit  of  3  per  cent,  except 
the  Jackson  Co.  coal,  the  average  of  which  is  4  per  cent  below.  The 
figures  from  Houghton's  tests  also  fall  within  the  limit  of  4  per  cent 
variation  from  the  Mahler  line,  except  coal  No.  4,  Brier  Hill,  0., 
which  falls  400  calories,  or  nearly  5  per  cent,  below  the  Mahler  line. 
The  Wyoming  coals  appear  to  belong  to  an  entirely  different  class 
from  any  of  the  Eastern  coals. 

Heating  Value  of  Wyoming  Coals. — The  following  table  is  con- 
densed from  a  report  by  Professors  E.  E.  Slosson  and  L.  C.  Colburn  of 
the  University  of  Wyoming,  Laramie,  Wyo.  (Special  Bulletin,  Jan., 
1895.) 


Coal. 

Combustible. 

Water. 

Volatile 
Matter. 

Fixed 
Carbon. 

J3 

00 

< 

h 

3 

jq 

a 
3 

CQ 

Calories. 

ll 

58.70 
60.67 
58.39 

60.72 
52  .  05 
59.63 

60.12 
55.14 
60.63 

56.38 
56.31 
57.13 

Calories. 

^ 

Hi 

pqa 

Uinta  Co  

2.95 

8.82 
5.80 

4.87 
13.65 
7.83 

5.55 
14.23 
8.65 

13.55 
14.70 
14.50 

38.00 
33.55 
36.16 

35.68 
39.25 
35.32 

36.95 
37.48 
34.86 

35.05 
34.30 
33.35 

54.00 
51.75 
51.78 

55.15 
42.60 
52.15 

55.70 
46.07 
53.69 

45.30 
44.20 
44.30 

4.95 
5.90 
6.26 

4.30 
4.50 
4.55 

1.80 
2.22 
2.71 

6.10 
6.80 
7.85 

o.'eo 

.77 
.80 
.71 

.86 
.44 
.75 

.'34 
.42 

7467 
6017 
6673 

7140 
5375 
6565 

7358 
5949 
6598 

5293 
4966 
4931 

8116 
7055 

7573 

7863 
6567 
7540 

7942 
7120 
7432 

6587 
6326 
6350 

14,609 
12,699 
13,631 

14,153 
11,821 
13,572 

14,296 
12,816 
13,378 

11,857 
11,387 
11,450 

tt       i  ( 

Av.  of  8  .    

Carbon  Co  

t  i         (  < 

Av.  of  7  

Sweetwater  Co  

«            « 

Av.  of  13  

Johnson  Co  1 

3  samples  1 

The  figures  in  the  last  three  columns  have  been  calculated  by  the 
author.  The  figures  in  the  first  two  lines  for  each  of  the  three  counties 
first  named  are  selected  so  as  to  show  respectively  the  coals  of  the 
highest  and  the  lowest  heating  value  per  pound  of  combustible  of  the 
samples  tested.  They  show  quite  a  large  range  of  variation  within 
the  limits  of  a  county.  The  heating  value  per  pound  combustible 


TESTS  OF  THE  HEATING  VALUE   OF  COALS. 


161 


apparently  bears  no  definite  relation  to  the  percentage  of  fixed  carbon 
in  the  combustible,  indicating  that  the  quality  of  the  volatile  matter 
is  variable.  Coals  from  Weston,  Natrona,  AJbany,  Fremont,  Sheridan, 
Crook,  and  Converse  counties  are  within  the  range  of  quality  of  the 
coals  given  in  the  table. 

The  Mahler  calorimeter  was  used  in  determining  the  heating 
values. 

The  Calorific  Power  of  Weathered  Coals. — Messrs.  R.  S.  Hale  and 
Henry  J.  Williams  of  Boston,  in  Trans.  Am.  Soc.  M.  E.,  vol.  xx.v 
1898,  p.  333,  give;  the  results  of  analyses  and  calorimetric  tests  (by 
Mr.  Williams's  bomb  calorimeter)  of  several  coals  which  had  been 
exposed  to  the  weather  for  eleven  months,  and  of  duplicate  samples 


ANALYSES    AND     HEATING     VALUES     OF    WEATHERED    AND     UNWEATHERED     COALS. 


Coal,  Prox. 
Anal. 

Ultimate  Analysis  of  Combustible. 

Combustible. 

1 

3 
0, 

-    £ 

li 

IS' 

43 

1 

2 

c 

S 

"3 
M 

||| 

"     T£ 

>£   . 

>  |  . 

^ffl 

e 

« 

'o 

^ 

1 

1 

1 

X 

I 

•"3 
*o 

liJ 

iii 

l|| 

ll 

« 

S 

<! 

5 

W 

0 

% 

s 

& 

& 

•3 

B 

1.61 

11.74 

78.94 

5.56 

9.55 

1.52 

4.43 

56.5 

14,406 

Ax 

1.91 

12.61 

79.59 

4.89 

9.75 

1.54 

4.23 

56.9 

14,065 

341 

C 

1.21 

8.69 

83.54 

5.69 

5.87 

1.63 

3.27 

63.6 

15,403 

15,461 

Dx 

1.07 

9.15 

82.55 

5.24 

7.94 

1.64 

2.62 

67.0 

14,792 

15,301 

611J 

P 

1.36 

8.97 

81.24 

5.90 

8.16 

1.79 

2.91 

58.0 

15,003 

Ex 

0.89 

10.02 

81.56 

5.67 

8.14 

1.69 

2.94 

57.8 

14,908 

95 

R 

1.07 

8.77 

82.47 

6.01 

6.81 

1.88 

2.83 

56.5 

15,353 

Sx 

1.39 

8.50 

82.15 

5.95 

7.10 

1.62 

3.17 

57.5 

15,260 

93 

I 

0.53 

4.34 

88.72 

5.22 

3.79 

1.74 

0.53 

77.2 

15,913 

Hx 

1.12 

6.32 

S8.05 

5.04 

4.08 

1.78 

1.04 

75.8 

15,705 

208 

K 

2.02 

10.08 

81.45 

5.62 

10.19 

1.66 

1.09 

61.2 

14,622 

/gain 

Jx 

1.46 

11.06 

81.33 

5.67 

9.88 

1.67 

1.45 

60.4 

14,685 

\   63 

0 

1.77 

8.44 

83.50 

5.67 

7.13 

1.79 

1.90 

58.5 

15,231 

15,240 

NX 

1.71 

10.47 

82.41 

5.74 

8.39 

1.67 

1.79 

61.4 

15,011 

15,200 

220  { 

L 

0.95 

5.75 

88.85 

5.19 

3.03 

2.07 

0.87 

78.2 

15,989 

16,048 

MX 

0.70 

7.77 

88.38 

4.77 

4.35 

1.60 

0.89 

80.6 

15,562 

15,958 

427J 

G* 

0.79 

7.51 

88.90 

4.82 

2.87 

2.04 

1.37 

80.0 

15,799 

Pof 

0.94 

7.06 

91.15 

4.75 

2.15 

1.28 

0.68 

80.6 

16,113 

*  Indoors  three  years.  t  Exposed  in  a  coal  yard  three  years. 

J  611,  220,  and  427,  loss  in  calculated  values.  160,  40,  and  90,  corresponding  loss  by 
calorimeter  tests. 

Reference  letters:  B.  C,  etc.,  unweathered  coals;  Ax,  Dx,  etc.,  weathered 
coals;  B,  A,  C,  D,  Yorkville  lump.  Porltand,  Ohio;  P.  E.  Pittsburg,  Pa.,  fine; 
R.  S.  do.,  lump;  I.  H.  New  River,  W.  Va.,  fine;  K.  J,  Nickel  Plate,  fine," McDonald 
Pa.;  O,  N,  do.,  lump;  L,  G,  M,  Georges  Creek,  Cumberland,  Md.,  fine;  Po, 
Pocahontas,  Va.,  fine. 


162  STEAM-BOILER  ECONOMY. 

of  the  same  coals  which  had  been  sealed  in  glass  jars.  The  results 
are  condensed  in  the  table  on  page  161.  The  following  notes  are 
extracted  from  the  paper : 

For  tests  of  fine  coal  the  samples  were  ground  in  a  coffee-grinder, 
and  thoroughly  mixed  and  divided  into  two  parts.  For  tests  of  lump 
coal  the  coals  were  broken  into  lumps  of  about  nut  size,  and  alternate 
lumps  taken  from  the  pile  to  form  two  samples.  Where  tests  of  both 
fine  and  lump  coal  were  to  be  made,  one  sample  was  tightly  sealed  in 
an  ordinary  pint  fruit  jar,  while  the  corresponding  sample  was  exposed 
on  an  uncovered  balcony  out  of  doors  for  eleven  months  in  an  un- 
covered tin  can  provided  with  a  diaphragm  or  bottom  of  fine  wire 
gauze. 

Rain  and  snow  fell  upon  the  coal,  but  the  wire  diaphragm  per- 
mitted the  water  to  drain  off,  while  a  paper  disk  placed  upon  the  wire 
gauze  prevented  the  coal  from  sifting  through  the  meshes. 

The  lump  samples  were  exposed  in  pans  of  much  larger  size,  which 
were  provided  with  holes  to  let  the  water  drain  off. 

At  the  end  of  eleven  months  all  the  samples  were  analyzed  by  Mr. 
Henry  J.  Williams,  together  with  a  sample  of  Pocahontas  coal  that 
had  been  exposed  in  a  coal-yard  for  three  years,  and  one  of  Cumber- 
land coal  that  had  been  under  cover  for  three  years. 

In  these  analyses  the  percentages  of  ash  in  some  of  the  exposed 
samples  are  unfortunately  too  high,  for  a  little  gravel  was  accidentally 
washed  off  the  roof  of  the  house,  by  the  rain,  into  some  of  the  cans. 
This,  however,  in  no  way  affects  the  relative  percentages  of  combust- 
ible matter  free  from  ash. 

The  British  thermal  units  are  calculated  from  the  analyses  by  the 
formula:  146C  +  620 (H— -J0)-f  40S. 

The  average  of  the  results  obtained  shows  that  weathering,  under 
the  conditions  described,  decreases  the  percentage  of  carbon,  hydro- 
gen, nitrogen;  increases  the  percentage  of  oxygen,  and  does  not 
materially  alter  the  percentage  of  sulphur. 

The  conclusions  to  be  drawn  from  an  examination  of  the  results 
shown  are : 

1st.  That  weathering  decreases  by  about  two  per  cent  the  theo- 
retical calorific  power,  as  calculated  by  Dulong's  formula. 

2d.  That  weathering  decreases  by  about  one-half  of  one  per  cent 
the  actual  or  true  calorific  power,  as  shown  by  the  three  results 
obtained  with  the  bomb. 

The  results  obtained  by  Messrs.  Hale  and  Williams  are  plotted  on 


TESTS  OF  THE  HEATING  VALUE  OF  COALS. 


163 


the  diagram  given  below,  with  relation  to  the  fixed  carbon  in  the 
combustible,  together  with  the  curve  obtained  from  Mahler's  tests. 
The  diagram  shows  that  all  the  coals  containing  over  59%  fixed  car- 
bon in  the  combustible  are  within  3%  of  the  corresponding  position 
in  the  curve,  with  the  exception  of  the  result  calculated  from  the 
ultimate  analysis  of  the  weather  coal  D.  The  exception  is  apparently 
due  to  an  error  in  the  analysis.  The  proximate  analysis  of  this  coal 
shows  an  increase  in  the  fixed  carbon  by  weathering  of  3.68%,  referred 
to  combustible,  while  the  ultimate  analysis  shows  a  decrease  in  the 
total  carbon  of  0.99%.  These  figures  appear  incompatible. 

•The  coals  containing  less  than  59%  fixed  carbon  show,  in  most 
cases,  a  wide  divergence  from  the  curve,  tending  to  confirm  the  con- 


O.T.y  CALORIE 

16020  8900 
15840  B300 
15CGO  8700 
15480  8600 
15300  8500 

8. 

F^p 

Jg 

~Q 

•mm 

/ 

.  . 

u 

^ 

—  _ 

2y 

sat 

ESS 

^. 

. 

Mx 

I* 

*!£. 

N^^ 

L^'*««* 

^ 

<-- 

"' 

'•c 

R 

15120  8400 
14940  8300 
14760  8200 
14580  8100 
14400  8000 
14220  7900 
14040  7300 
138CO  7700 

> 

^ 

NX 

— 

— 

^ 

Sx 

— 

/ 

^ 

^ 

^ 

P 

L,0,a,C,ETC.UNWEATHEREO  COALS. 

MX,  Hx,  Ox,  ETC.  WEATHERED  COALS. 

THE  POSITIONS  JOINED  OY  DOTTED  LINES 
REPRESENT  RESULTS  OF  CALORIMETRIC 
DETERMINATIONS;  THOSE  JOINED  BY 
FULL  LINES  SHOW  RESULTS  CALCULATED 
FROM  ANALYSES. 

Ox 

/ 

\ 

*Ex 

K, 

^*J 

\ 

\ 

B 

f 

— 

\ 

/ 

\ 

| 

1 

Ax 

50 

FIG.  10. — HEATING  VALUE  OF  WEATHERED  AND  UNWEATHEEED  COALS. 

elusion  drawn  from  the  work  of  Lord  and  Haas,  that  among  the 
highly  volatile  coals  each  class  of  coal  has  a  law  of  its  own. 

Coals  AB  and  CD,  both  said  to  be  Portland  lump,  from  Yorkville, 
Ohio,  show  such  a  great  difference  in  percentage  of  fixed  carbon  and 
in  heating  value  that  they  appear  to  belong  to  entirely  different  classes 
of  coal.  It  would  be  interesting  to  know  whether  these  samples  came 
from  the  same  seam  or  from  different  seams.  If  from  the  same  seam, 
the  figures  would  indicate  that  the  conclusion  of  Professors  Lord  and 
Haas,  that  the  coals  mined  from  one  seam  over  a  considerable  area  of 
country  have  a  nearly  uniform  heating  value,  has  some  exceptions. 

It  should  be  noted  that  the  loss  in  heating  value  per  pound  of  the 
combustible  portion  of  the  coal  may  not  be  a  true  measure  of  the 
actual  loss  in  heating  value  of  the  whole  of  a  given  lot  of  coal,  for 
besides  the  loss  in  heating  value  per  pound  there  may  be  also  a  loss  in 


164  STEAM-BOILER  ECONOMY. 

weight,  and  this,  if  any,  expressed  as  a  percentage,  should  be  added  to 
the  loss  in  heating  value  per  pound.  On  the  other  hand,  there  may  be 
a  gain  in  weight  due  to  oxidation.  In  most  of  these  samples  the 
oxygen  seems  to  have  increased. 

Investigations  of  the  deterioration  by  weathering  of  different 
types  of  coal  were  made  in  1910  by  the  Bureau  of  Mines.  To  deter- 
mine the  loss  of  volatile  matter  during  storage  20-pound  samples  were 
broken  to  J-inch  size  at  the  mine  and  placed  in  bottles.  At  the 
laboratory  the  accumulated  gas  was  withdrawn  and  a  continuous 
escape  of  gas  permitted  at  atmospheric  pressure  and  temperature. 
Several  coals  were  found  to  evolve  methane  in  large  volumes  in  the 
early  period  after  mining,  but  the  maximum  loss  in  calorific  value 
from  this  cause  was  only  0.16  per  cent.  (See  Technical  Paper  No. 
2,  "The  Escape  of  Gases  from  Coal.") 

It  seems  therefore  that  the  loss  due  to  escape  of  volatile  matter 
from  coal  has  been  greatly  overestimated. 

More  elaborate  tests  were  undertaken  to  determine  the  total  loss 
possible  in  high-grade  coal  by  weathering,  and  the  extent  of  the  saving 
to  be  accomplished  by  water  submergence  as  compared  to  open-air 
storage,  also  whether  salt  water  possessed  any  advantage  over  fresh 
water  for  this  purpose. 

Four  kinds  of  coal  were  chosen:  New  River  on  account  of  its 
large  use  by  the  Navy,  Pocahontas  as  a  widely  used  steaming  and 
coking  coal  in  the  eastern  section,  Pittsburgh  coal  as  a  type  of  rich 
coking  and  gas  coal,  and  Sheridan  (Wyo.)  sub-bituminous  or  "black 
lignite" — a  type  much  used  in  the  West.  With  the  New  River  coal, 
50-lb.  portions  were  crushed  to  f-inch  size  and  well  mixed.  These 
portions  confined  in  perforated  wooden  boxes  were  submerged  under 
sea  water  at  three  Navy  Yards,  differing  widely  from  each  other 
in  climatic  conditions,  and  300-lb.  portions  from  the  same  original  lot 
were  exposed  to  the  open  air,  both  out  of  doors  and  indoors,  at  the 
same  places. 

The  New  River  coal  showed  a  loss  of  less  than  1  per  cent 
calorific  value  in  one  year  by  weathering  in  the  open.  There  was 
practically  no  loss  at  all  in  the  samples  submerged  in  either  fresh  or 
salt  water.  Pocahontas  coal  in  a  120-ton  pile  on  the  Isthmus  of 
Panama  lost  in  one  year  less  than  0.4  per  cent  in  heating  value. 

The  Pittsburgh  gas  coal  during  six  months  of  outdoor  exposure 
suffered  no  loss  whatever  of  calorific  value,  measurable  by  the  calori- 


TESTS  OF  THE  HEATING   VALUE  OF  COALS.  165 

metric  method  used,  not  even  in  the  upper  surface  layer  of  the  bins. 
The  Wyoming  coal,  however,  sustained  a  loss  of  over  5  per  cent. 

Illinois  coal  has  been  found  by  Prof.  S.  W.  Parr  and  Mr.  A. 
Bement  to  suffer  a  loss  in  heating  value  of  from  1  to  3  per  cent  on 
exposure  for  a  year. 

Weathering  of  Coal. — The  practical  effect  of  the  weathering  of 
coal,  while  sometimes  increasing  its  absolute  weight,  is  to  diminish 
the  quantity  of  carbon  and  disposable  hydrogen  and  to  increase  the 
quantity  of  oxygen  and  of  indisposable  hydrogen.  Hence  a  reduction 
in  the  calorific  value. 

An  excess  of  pyrites  in  coal  tends  to  produce  rapid  oxidation  and 
mechanical  disintegration  of  the  mass,  with  development  of  heat, 
loss  of  coking  power,  and  spontaneous  ignition. 

The  only  appreciable  results  of  the  weathering  of  anthracite  within 
the  ordinary  limits  of  exposure  of  stocked  coal  are  confined  to  the 
oxidation  of  its  accessory  pyrites.  In  coking  coals,  however,  weather- 
ing reduces  and  finally  destroys  the  coking  power,  while  the  pyrites 
are  converted  from  the  state  of  bisulphide  into  comparatively  in- 
nocuous sulphates. 

Eichters  found  that  at  a  temperature  of  158°  to  180°  Fahr.,  three 
coals  lost  in  fourteen  days  an  average  of  3.6%  of  calorific  power. 

It  appears  from  the  experiments  of  Eichters  and  Eeder  that  when 
there  is  no  rise  in  the  temperature  of  coal  piled  in  heaps  and  left 
exposed  to  the  air  during  nine  to  twelve  months,  it  undergoes  no 
sensible  change  in  any  respect ;  and  that,  on  the  other  hand,  when  the 
coal  becomes  heated,  it  suffers  precisely  the  same  kind  of  change  that 
was  found  by  Eichters  to  be  effected  in  coal  by  heating  it  in  contact 
with  atmospheric  air  to  a  comparatively  low  temperature,  namely  loss 
of  carbon  and  hydrogen  by  oxidation  and  increase  of  the  absolute 
weight  of  the  coal  owing  to  the  fixation  of  oxygen.* 

Deterioration  of  Coal  in  Storage. —  (A.  Bement,  Power.  June  25, 
1912.)  Four  samples  of  air-dry  coal,  400  Ibs.  each,  were  stored  in  a 
box  for  a  year.  The  box  was  covered  with  cheesecloth  to  exclude  dirt. 
Two  other  samples  were  stored  under  water.  The  coals  were  analyzed 
and  their  heating  power  was  determined  by  a  Mahler  calorimeter. 
The  changes  in  weight  and  in  heating  power  were  as  follows : 

*  Reports  of  Second  Geological  Survey  of  Pennsylvania,  vol.  M.M.,  p.  113; 
also  Percy's  "  Metallurgy:  "Refractory  Materials  and  Fuel,"  1873.  See  also 
papers  by  R.  P.  Roth  well,  Trans.  A.  I.  M.  E.,  vol.  iv,  p.  55,  and  by  I.  P. 
Kimball,  Trans.  A.  I.  M.  E.,  vol.  viii,  p.  204. 


166 


STEAM-BOILER  ECONOMY. 


Coal. 

A. 

B. 

C. 

D. 

Volatile  matter  in  combustible,  %  
Heatine  nower  of  comb..  B.T.U.  . 

41.1 
15.048 

39.7 
14.575 

48.6 
14.350 

47.9 
14.250 

CHANGE    DUE    TO    EXPOSURE    IN    AIR    FOR   A    YEAR 


Heating  power,  % 
Weight,  % 


-.025 
0.00 


-0.38 
+0.11 


-0.93 
-1.15 


CHANGE    AFTER    STORAGE    FOR   A    YEAR    UNDER   WATER 


-1.85 

-2.25 


Heating  power  % 

+0  02 

-0  44 

Weight,  %  

-0.81 

-0.35 

CHAPTER  VI. 
FUELS   OTHER   THAN   COAL. 

Coke, — Coke  is  the  solid  material  left  after  evaporating  the  vola- 
tile ingredients  of  coal,  either  by  means  of  partial  combustion  in 
furnaces  called  coke-ovens,  or  by  distillation  in  the  retorts  of  gas- 
works. Being  a  smokeless  fuel  it  is  available  for  use  in  the  fire-boxes 
of  internally  fired  boilers,  which  are  not  adapted  to  the  smokeless 
combustion  of  soft  coal,  but  its  use  for  this  purpose  is  quite  limited 
on  account  of  its  cost. 

The  proportion  of  coke  yielded  by  a  given  weight  of  coal  is  very 
different  for  different  kinds  of  coal,  ranging  from  35  to  90  per  cent. 

Being  of  a  porous  texture,  it  readily  attracts  and  retains  water 
from  the  atmosphere,  and  sometimes,  if  it  is  kept  without  proper 
shelter,  from  15  to  20  per  cent  of  its  gross  weight  consists  of  moisture. 

ANALYSIS   OF   COKE. 
(From  report  of  John  R.  Procter,  Kentucky  Geological  Survey.) 


Where  Made. 

Fixed 
Carbon. 

Ash. 

Sulphur. 

Connellsville,  Pa.       (Average 
Chattanooga,  Tenn. 
Birmingham,  Ala. 
Pocahontas,  Va. 
New  River,  W.  Va. 
Big  Stone  Gap,  Ky. 

of  3  samples)  .... 
4       '          
4       '          

3       ' 

8       ' 

7       ' 

88.96 
80.51 
87.29 
92.53 
92.38 
93.23 

9.74 
16.34 
10.54 
5.74 
7.21 
5.69 

0.810 
1.595 
1.195 
0.597 
0.562 
0.749 

Pressed  Fuel  or  Briquettes, — A  method  of  making  pressed  fuel 
from  anthracite  dust  is  described  by  E.  P.  Loiseau.*  The  dust  is 
mixed  with  ten  per  cent  of  its  bulk  of  dry  pitch,  which  is  prepared  by 
separating  from  tar  at  a  temperature  of  572°  F.  the  volatile  matter 
it  contains.  The  mixture  is  kept  heated  by  steam  to  212°,  at  which 
temperature  the  pitch  acquires  its  cementing  properties,  and  is  passed 
between  two  rollers,  on  the  periphery  of  which  are  milled  out  a  series 


Trans.  A,  I.  M.  E.,  vol.  viii,  p.  314, 


167 


168  STEAM-BOILER  ECONOMY. 

of  semi-oval  cavities.  The  lumps  of  the  mixture,  about  the  size  of  an 
egg,  drop  out  under  the  rollers  on  an  endless  belt  which  carries  them 
to  a  screen  in  eight  minutes,  which  time  is  sufficient  to  cool  the  lumps, 
and  they  are  then  ready  for  delivery. 

The  enterprise  of  making  the  pressed  fuel  above  described  was  not 
commercially  successful,  on  account  of  the  low  price  of  other  coal. 
In  Europe,  however,  ''briquettes"  are  regularly  made  of  coal-dust 
(bituminous  and  semi-bituminous)  and  of  lignite. 

Tests  of  Briquettes.— Bulletin  403  of  the  U.  S.  Geological  Survey, 
1909,  contains  a  report  of  comparative  tests  of  run-of-mine  semi- 
bituminous  coal  and  the  same  coal  briquetted,  in  a  Normand  water- 
tube  marine  boiler.  The  binder  used  in  the  briquettes  was  6  per 
cent  of  water-gas  pitch.  On  a  boiler  rating  of  10  square  feet  per 
H.  P.  tests  were  made  at  several  rates  of  driving  from  100  to  300 
per  cent  of  rating.  Practically  no  difference  was  found  in  effi- 
ciency between  the  coal  and. the  briquettes.  In  both  the  equivalent 
evaporation  per  pound  of  dry  coal  fired  was  about  10  Ibs.  and  100 
per  cent  of  rating  and  8  Ibs.  at  300  per  cent.  The  furnace  condi- 
tions were  in  general  better  at  the  higher  rates,  the  air  supply  at 
the  lower  rates  of  driving  being  excessive.  The  briquettes  made  as 
much  (or  more)  smoke  as  run-of-mine  coal,  and  with  briquettes  the 
storage  capacity  of  a  bunker  is  reduced  by  23  to  27  per  cent. 

In  1910  the  German  Empire  produced  19^561,494  metric  tons  of 
briquettes,  of  which  15,120,255  metric  tons,  or  77  per  cent  of  the 
total  output,  were  made  from  lignite.  These  lignite  briquettes  are 
much  liked  for  domestic  use,  and  form  the  chief  household  fuel  in 
many  large  cities. 

The  U.  S.  Geological  Survey  in  1904  investigated  the  merits  of 
lignite  as  a  fuel,  with  the  object  of  ascertaining  the  most  efficient 
methods  of  utilizing  it.  Briquetting  tests  of  lignite  were  made  and  also 
combustion  tests  of  lignite  briquettes  and  of  raw  lignite  in  boiler 
furnaces  and  in  gas  producers.  (See  Geological  Survey  Bulletins 
261,  290,  332,  343,  and  363,  Professional  Paper  48.) 

Briquetting  tests  of  lignite  were  undertaken  in  1909  by  the  U.  S. 
Bureau  of  Mines  to  ascertain: 

1.  The  possibility  of  briquetting  American  lignites  without  add- 
ing binder  to  them. 

2.  The  suitability  of  the  German  brown-coal  briquette  presses  for 
briquetting  American  lignites. 

3.  The  percentage  of  moisture  needed  in  the  briquette  material  to 
give  the  best  briquettes. 

4.  The  approximate  commercial  cost  of  briquetting  lignites. 

5.  The  weathering  qualities  of  briquettes  as  compared  with  raw 
lignites. 


FUELS  OTHER  THAN  COAL. 


169 


The  results  were  not  conclusive,  but  they  warrant  the  continua- 
tion of  the  investigations  as  soon  as  funds  are  available  for  the 
purpose.  Enough  testing  waS~done  to  indicate  that  some  American 
lignites  equal  German  lignites  in  fuel  value  and  can  probably  be 
made  into  briquettes  on  a  commercial  scale  without  the  use  of  binding 
materials.  Three  samples  of  lignite,  one  from  Texas,  one  from  North 
Dakota,  and  one  from  California,  were  made  into  satisfactory  briquettes 
without  the  addition  of  a  binder.  It  was  proved  that  some  lignites 
after  having  slacked  by  exposure  can  be  made  into  briquettes  with- 
out the  use  of  binding  material.  Cohesion  and  weathering  tests 
demonstrated  that  good  briquettes  endure  handling  and  resist  weath- 
ering much  better  than  the  lignite  from  which  they  are  made.  Bulletin 
14,  U.  S.  Bureau  of  Mines. 

Experiments  on  briquetting  of  anthracite  culm  and  a  description 
of  a  briquetting  plant  are  given  in  a  paper  by  Chas.  Dorrance,  Jr., 
in  Trans.  A.  I.  M.  E.,  1911. 

Briquetted  Coal  in  Locomotives, — The  results  of  a  series  of  tests 
with  raw  and  briquetted  coal  made  at  the  locomotive  testing  plant 
of  the  Penna.  R.  R.  Co.  were  reported  at  the  annual  meeting  of  the 
Am.  Rwy.  Master  Mechanics  Assn.  in  1908. 

The  accompanying  table  taken  from  a  plot  of  actual  results  shows 
comparatively  the  evaporation  of  the  natural  and  briquetted  coal. 

BOILER   EVAPORATION   WITH    RAW    AND    BRIQUETTED    FUEL. 


Rate  of  Evaporation  per 
Square  Foot  Heating  Surface. 

Equivalent  Evaporation  per  Pound  of  Fuel. 

Natural  Lloydell  Coal. 

Briquetted  Coal. 

81bs. 
10   " 
12    " 
14    " 
16    " 

9.5  Ibs. 
8.8   " 
8.0   " 
7.3    " 
6.6    " 

10.71bs. 

10.2   " 
9.7   " 
9.2    " 

8.7   " 

The  quantity  of  cinders  collected  in  the  smoke-box  showed  no 
material  difference  as  between  the  raw  coal  and  the  briquetted  coal. 

Fire-box  and  smoke-box  temperatures  were  practically  the  same 
at  the  same  rates  of  evaporation,  whether  the  coal  was  used  in  its  raw 
state  or  briquetted. 

The  apparent  reason  for  the  increased  evaporation  per  pound  of 
fuel  with  the  briquetted  coal  is  that,  although  the  loss  due  to  cinders 
in  the  smoke-box  is  not  different  as  judged  by  the  quantity  collected, 
the  calorific  value  of  the  cinders  from  the  briquetted  coal  was  lower 
than  with  raw  coal,  and,  further,  on  account  of  the  uniform  size 
of  the  briquetted  fuel  the  distribution  of  air  through  the  fire  per- 
mitted more  complete  combustion  and  liberation  of  heat  than  with  the 
raw  coal. 


170  STEAM-BOILER  ECONOMY. 

Binders  for  Coal  Briquettes. — The  results  of  experiments  on  the 
use  of  different  materials  as  binders  for  briquetting  coal  are  re- 
ported in  Bulletin  343  of  the  U.  S.  Geological  Survey,  1908. 

The  experiments  show  that,  in  general,  for  plants  situated 
where  it  can  be  obtained,  the  cheapest  binder  will  prove  to  be  the 
heavy  residuum  from  petroleum,  often  known  to  the  trade  as  asphalt. 
Four  per  cent  of  this  binder  being  sufficient,  its  cost  ranges  from 
45  to  '60  cts.  per  ton  of  briquettes  produced.  This  binder  is  partic- 
ularly available  in  California,  Texas  and  adjacent  territory.  Second 
in  order  of  importance  comes  water-gas  tar  pitch.  Five  or  six  per 
cent  usually  proving  sufficient,  the  cost  of  this  binder  ranges  from 
50  to  60  cts.  per  ton  of  briquettes  produced.  As  water-gas  pitch  is 
also  derived  from  petroleum,  it  will  be  available  more  particularly 
in  oil-producing  regions.  Third  in  order  of  importance  is  coal- 
tar  pitch.  Being  derived  from  coal,  this  binder  is  very  widely 
available.  From  6.5  to  8  per  cent  will  usually  be  required,  and  the 
cost  ranges  from  65  to  90  cts.  per  ton  of  briquettes  produced. 

The  briquetting  of  lignite  offers  a  peculiarly  difficult  problem. 
If  the  lignite  cakes  in  the  fire,  asphaltic  residues  from  petroleum 
or  water-gas  tar  pitch  may  be  used  as  binder,  larger  percentages 
being  required  than  for  ordinary  coals.  The  most  promising  binders 
for  lignites  that  do  not  cake  are  starch,  sulphite  liquor  from  paper 
mills,  and  magnesia.  Lignites  may  be  briquetted  without  binder 
if  they  are  to  be  burned  on  grates  especially  constructed  to  over- 
come the  tendency  to  fall  to  pieces  in  the  fire. 

The  main  problem  in  briquetting  is  to  find  a  suitable  binding 
material  at  sufficiently  low  cost.  When  the  difference  in  price 
between  the  slack  coal  and  the  first-class  lump  coal  is  $1,  the  cost 
of  briquetting  should  not  exceed  this  amount.  Of  this  the  binder 
must  cost  less  than  60  cents  per  ton,  as  the  cost  of  manufacture 
averages  about  40  cents. 

Coal-dust. — Dust  when  mixed  in  air  burns  with  such  extreme 
rapidity  as  in  some  cases  to  cause  explosions.  Explosions  of  flour- 
mills  have  been  attributed  to  ignition  of  the  dust  in  confined  pas- 
sages. Experiments  made  in  Germany  in  1893  show  that  pulverized 
fuel  may  be  burned  without  smoke,  and  with  high  economy.  The  fuel, 
instead  of  being  introduced  into  the  fire-box  in  the  ordinary  manner, 
is  first  reduced  to  a  powder  by  pulverizers  of  any  construction.  In 
the  place  of  the  ordinary  boiler  fire-box  there  is  a  combustion-chamber 
in  the  form  of  a  closed  furnace  lined  with  fire-brick  and  provided  with 
an  air-injector  similar  in  construction  to  those  used  in  oil-burning 
furnaces.  The  nozzle  throws  a  constant  stream  of 'the  fuel  into  the 
chamber.  This  nozzle  is  so  located  that  it  scatters  the  powder  through- 
out the  whole  space  of  the  fire-box.  When  this  powder  is  once 


FUELS  OTHER  THAN  COAL.  171 

ignited,  which  is  readily  done  by  first  raising  the  lining  to  a  high 
temperature  by  an  open  fire,  the  combustion  continues  in  a  regular 
manner  under  the  action  of  the  current  of  air  which  carries  it  in. 

Powdered  fuel  was  used  in  the  Compton  rotary  puddling-furnaoe 
at  Woolwich  Arsenal,  England,  in  1873.*  It  is  used  with  great  success 
in  this  country  in  the  rotary  kilns  used  in  the  manufacture  of  Portland 
cement. 

The  American  Manufacturer  of  Dec.  13,  1900,  illustrates  the 
Cyclone  Pulverizer,  a  British  invention,  which  is  said  to  be  in  suc- 
cessful use  grinding  coal  for  dust-firing.  We  quote  from  it  the  follow- 
ing statement  of  the  requisite  conditions  of  success  in  the  use  of 
powdered  fuel,  and  of  the  advantages  claimed  for  it: 

The  best  results  can  only  be  obtained  when  the  following  essentials 
are  complied  with,  viz. : 

(a)  The  fuel  must  be  reduced  cheaply  to  a  very  finely  divided 
powder,  and  must  be  of  a  strictly  uniform  grade. 

(b)  The  coal-powder  mixed  with  air  must  be  carried  in  an  un- 
broken stream  into  the  combustion-chamber. 

(c)  The  air  current  must  be  so  regulated  that  it  will  hold  the 
coal-powder  in  suspension,  when  within  the  furnace,  until  complete 
combustion  is  effected. 

(d)  A  sufficiently  high  temperature  must  be  continuously  main- 
tained in  the  furnace,  to  ensure  perfect  combustion  of  the  powder. 

The  problem  of  how  to  reduce  the  coal  economically  to  the  required 
standards  of  fineness  and  uniformity  is  the  one  thing  which  has  given 
great  trouble  in  developing  new  devices  in  firing-apparatus. 

The  advantages  of  the  use  of  powdered  fuel  may  be  summarized  as 
follows :  1.  The  most  economical  and  complete  combustion  of  the 
fuel,  in  a  manner  similar  to  gas-firing,  but  without  the  disadvantages 
of  that  system.  2.  Complete  smokelessness.  3.  Eeduced  labor  ex- 
penses, since  one  man  can  easily  manage  several  furnaces.  4.  Adapta- 
bility and  ease  of  regulation  to  meet  any  requirements,  especially  when 
the  work  is  that  of  steam-generation.  5.  Decreased  wear  and  tear  of 
furnaces,  in  the  case  of  internally  fired  boilers.  6.  Saving  of  time 
in  starting  up  furnaces,  and  rapid  stoppage  of  firing,  in  case  of  neces- 
sity. 7.  Less  labor  in  removing  refuse,  which  is  light  in  quantity, 
and  in  the  form  of  slag.  8.  Intimate  contact  of  the  fuel  with  the  air, 
whereby  the  minimum  excess  over  the  theoretical  volume  is  employed, 
and  waste  of  heat  thus  avoided. 

Notwithstanding  the  advantages  above  stated,  there  is  no  prospect 
that  the  use  of  powdered  coal  for  steam  making  will  ever  become  ex- 
tensive. F.  R.  Low,  in  a  paper  on  Pulverized  Coal  for  Steam  Making, 

*  Journal  of  the  Iron  and  Steel  Institute,  i.,  1873,  p.  91. 


172  '  STEAM-BOILER  ECONOMY. 

(Jour.  A.  8.  M.  E.,  Oct.  1914),  says:  Numerous  attempts  have  been 
made  in  the  past  quarter  century  to  use  pulverized  coal  as  a  boiler  fuel. 
The  published  accounts  of  the  various  trials  are  full  of  promise  and 
apparent  accomplishment,  but  few  of  the  processes  have  persisted,  and 
only  a  small  proportion  of  the  coal  used  in  steam  making  is  fired  iii  this 
way.  The  cost  of  pulverizing  and  the  large  initial  cost  of  the  drying, 
pulverizing,  conveying  and  feeding  apparatus,  together  with  the  fact 
that  coal  of  practically  all  grades  can  be  burned  with  a  tolerable  degree 
of  smokelessness  in  the  cheaper  apparatus  in  common  use  with  a  degree 
of  efficiency  which  leaves  little  margin  to  cover  the  increased  expendi- 
ture, have  combined  to  restrict  the  use  of  pulverized  coal  for  boiler 
purposes  to  special  instances. 

Peat  or  Turf,  as  usually  dried  in  the  air,  contains  from  25%  to 
30%  of  water,  which  must  be  allowed  for  in  estimating  its  heat  of 
combustion.  This  water  having  been  evaporated,  the  analysis  of  M. 
Regnault  gives,  in  100  parts  of  perfectly  dry  peat  of  the  best  quality : 
C  58%,  H  6%,  0  31%,  Ash  5%. 

In  some  examples  of  peat  the  quantity  of  ash  is  greater,  amount- 
ing to  7%  and  sometimes  to  11%.  The  specific  gravity  of  peat  in  its 
ordinary  state  is  about  0.4  or  0.5.  It  can  be  compressed  by  machinery 
to  a  much  greater  density.  (Rankine.) 

Clark  ("Steam-engine/'  vol.  i,  p.  61)  gives  as  the  average  compo- 
sition of  dried  Irish  peat:  C  59%,  H  6%,  0  30%,  N  1.25%,  Ash  4%. 

Applying  Dulong's  formula  to  this  analysis,  we  obtain  for  the 
total  heating  value  of  perfectly  dry  peat  10,009  heat-units  per  pound, 
and  for  air-dried  peat  containing  25%  of  moisture  7507  heat-units  per 
pound.  To  determine  the  "available"  heating  value,  we  must  sub- 
tract the  heat  lost  in  the  superheated  steam  in  the  chimney-gases,  as 
calculated  by  the  formula  on  page  26.  For  each  pound  of  the  air- 
dried  peat  the  superheated  steam  is  0.25  +  0.75  X  .06  X  9  =  0.655 
Ibs. ;  and  if  the  temperature  of  the  chimney-gases  is  462°  and  that  of 
the  air-supply  62°  the  heat  lost  is 

0.655  X  [(212  -  62)  +  970  +  (0.48  X  250)]  =  812  B.T.U. 


This  subtracted  from  7507  gives  6695  B.T.U.  as  the  available  heating 
value  per  pound  of  peat. 

Deposits  of  peat  are  found  in  many  places  throughout  the  United 
States  and  Canada,  but  it  has  hitherto  not  been  found  practicable, 
commercially,  to  utilize  them  for  fuel  in  competition  with  coal.  In 


FUELS  OTHER  THAN  COAL. 


173 


some  countries  in  Europe,  such  as  in  Holland  and  Denmark,  the  peat 
industry  is  quite  common.  Papers  on  peat  and  its  utilization  will  be 
found  in  "Mineral  Industry,"  vol.  ii.,  1893,  and  vol.  vii.,  1898.  The 
following  table  is  given  showing  the  comparative  and  calorimetric 
value,  analyses  of  wood,  peat,  and  coal,  from  a  report  made  in  Sweden 
in  1896.  The  analyses  are  of  the  fuel  dry  and  free  from  ash. 


Composition. 

Wood. 

Peat. 

Brown 
Coal. 

Swedish 
Coal. 

English 
Steam 
Coal. 

Welsh 
Anthracite. 

Carbon  
Hydrogen  
Oxygen  
Sulphur 

52.0 
6.2 
41.7 

58.0 
5.7 
35.0 

66.0 
4.6 
28.0 

78.0 

5.1 

14.8 
0.8 

81.0 
5.2 

11.5 
1.0 

91.0 
3.5 
3.5 
1.0 

Nitrogen  

0.1 

1.2 

1.0 

1.3 

1.3 

1.0 

Calories 

4900 

5,700 

6,000 

7,500 

8,000 

8,600 

B.  T.  U  

8920 

10,260 

10,800 

13,500 

14,400 

15,480 

Moisture  

20 

22 

25 

13.5 

7.6 

2,0 

Production  of  Peat  Fuel  in  the  United  States. — The  production 
and  uses  of  peat  for  fuel  and  other  purposes  are  discussed  by  Charles 
A.  Davis  in  "Mineral  Resources,"  1910  (U.  S.  Geological  Survey) 
and  also  in  Bulletin  16  of  the  U.  S.  Bureau  of  Mines,  1911.  He 
says: 

As  yet  no  peat-fuel  industry  can  be  said  to  exist  in  the  United 
States,  although  much  experimental  work  has  been  done  and  great 
sums  of  money  spent  to  establish  one.  In  Europe  the  peat  beds  of 
various  nations  are  the  source  of  raw  materials  for  industries  of  some 
magnitude,  although  their  development  is  still  in  an  experimental 
stage. 

The  only  peat-fuel  plant  erected  in  the  United  States  in  1910  was 
that  of  the  Peat  Products  Co.,  at  Lakeville,  Ind.  The  peat  is  dug 
by  a  centrifugal  pump,  pumped  to  storage  bins,  and,  after  some 
of  the  water  has  drained  away,  dried  in  a  drier  heated  by  exhaust 
steam  and  stack  gases.  When  dry,  the  peat  is  reduced  to  .powder, 
conveyed  to  a  press,  and  compressed  into  compact  briquettes.  The 
production  of  peat  for  fuel  in  the  United  States  during  1910  was 
very  small.  No  figures  have  been  obtainable  as  to  their  production. 

Peat  fuel  may  be  said  to  be  especially  useful  for  certain  pur- 
poses for  which  wood  was  formerly  in  general  use  and  for  which 
coal  has  not  yet  been  altogether  successfully  introduced,  such  as  brick 
and  other  forms  of  ceramic  firing  ajid  lime  burning.  It  appears  to 
reach  its  highest  value,  however,  as  a  source  of  producer  gas  in 
properly  constructed  gas  producers,  Although  the  outlook  and 


174 


STEAM-BOILER  ECONOMY. 


European  experience  warrant  further  investigation  of  its  possible 
uses  and  value,  no  final  conclusions  as  to  the  commercial  value  of 
American  peat  as  compared  with  coal  can  be  reached. 

During  a  part  of  1910  the  Mines  Branch  of  the  Canada  Depart- 
ment of  Mines  operated  on  a  commercial  basis  a  demonstration  peat- 
fuel  plant.  This  was  located  at  Alfred,  Ontario,  about  30  miles 
from  Ottawa,  and  was  equipped  with  Swedish  machinery.  Part  of 
the  1600  tons  of  air-dried  machine  peat  produced  by  the  plant  was 
sold,  and  part  was  used  in  th-e  gas-producer  plant  established  by  the 
Government  in  Ottawa  for  testing  peat,  lignite,  and  similar  fuel. 
These  plants  are  fully  described  in  Bull.  4,  Can.  Dept.  of  Mines, 
Mines  Branch,  2d  edition,  1910. 

Wood. — Wood,  when  newly  felled,  contains  a  proportion  of  moist- 
ure which  varies  greatly  in  different  kinds  and  in  different  specimens, 
ranging  between  30%  and  50%,  and  being  on  an  average  about  40%. 
After  eight  or  twelve  months'  ordinary  drying  in  the  air  the  propor- 
tion of  moisture  is  from  20%  to  25%.  This  degree  of  dryness,  or 
almost  perfect  dryness  if  required,  can  be  produced  in  a  few  days7 
drying  in  an  oven  supplied  with  air  at  about  240°  F. 

Perfectly  dry  wood  contains  about  50%;  of  carbon,  the  remainder 
consisting  almost  entirely  of  oxygen  and  hydrogen  in  nearly  the  pro- 
portions which  form  water,  the  hydrogen  being  somewhat  in  excess. 
The  coniferous  family  contains  a  small  quantity  of  turpentine,  which 
is  a  hydrocarbon. 


ANALYSIS  OF  WOODS,  BY  M.  EUGENE  CHEVANDIER. 


Woods. 

Composition. 

Carbon. 

Hydrogen. 

Oxygen. 

Nitrogen. 

Ash. 

Beech. 

49  36% 

6.01% 

42  69% 

0   91% 

1  06% 

Oak 

49  64 

5.92 

41  16 

1    29 

1  97 

Birch 

50  20 

6  20 

41  62 

1    15 

0  81 

Poplar 

49.37 

6.21 

41.60 

0.96 

1.86 

Willow. 

49.96 

5.96 

39  56 

0.96 

3.37 

Average  

49.70% 

6.06% 

41.30% 

1.05% 

1.80% 

Heating  Value  of  Wood. — According  to  a  table  by  S.  P.  Sharpless,* 
the  ash  varies  from  0.03%  to  1.20%  in  American  woods,  and  the  fuel 


*  Journal  of  the  Charcoal  Iron  Workers'  Association,  vol.  iv,  p.  36. 


FUELS  OTHER  THAN  COAL.  175 

value  ranges  from  3667  (for  white  oak)  to  5546  calories  (for  long- 
leaf  pine)  =  6600  to  9883  British  thermal  units  for  dry  wood. 

The  following  table  is  given  in  several  books  of  reference,  the 
authority  and  quality  of  coal  referred  to  not  being  stated. 

The  weight  of  one  cord  of  different  woods  (thoroughly  air-dried) 
is  about  as  follows : 

Hickory  or  hard  maple.  .  .4500  Ibs.  equal  to  1800  Ibs.  coal.  (Others  give  2000.) 

White  oak.. 3850        "       "       1540        "  (  "        1715.) 

Beech,>ed  and  black  oak.. 3250'      "       "       1300        "  (  "        1450.) 

Poplar,  chestnut,  and  elm .  2350        "       "         940      J*  (  "        1050.) 

The  average  pine 2000       «       «        800      ""  (  "          925.) 

Referring  to  the  figures  in  the  last  column,  it  is  said: 

From  the  above  it  is  safe  to  assume  that  2J  Ibs.  of  dry  wood  are 
equal  to  1  Ib.  average  quality  of  soft  coal  and  that  the  fuel  value  of 
the  same  weight  of  different  woods  is  very  nearly  the  same — that  is,  a 
pound  of  hickory  is  worth  no  more  for  fuel  than  a  pound  of  pine, 
assuming  both  to  be  dry.  It  is  important  that  the  wood  be  dry,  as 
each  10%  of  water  or  moisture  in  wood  will  detract  about  12%  from 
its  value  as  fuel. 

Taking  an  average  wood  of  the  analysis,  perfectly  dry,  C.  50; 
H,  6 ;  0,  42 ;  N"  and  ash,  2,  its  total  heating  value,  by  Dulong's 
formula,  is  7765  B.T.U.  per  pound.  If  the  wood  contains  25%  of 
moisture  the  analysis  of  the  moist  wood  is  C,  37.5;  H,  4.5;  0,  31.5; 
N  and  ash,  1.5,  and  its  total  heating  value  is  75%  of  7765,  or  5824 
B.T.IT,  per  pound.  To  obtain  the  "available"  heating  value  we 
subtract  the  loss  of  heat  in  the  steam  formed  from  the  water  and  the 
hydrogen  in  the  wood,  as  calculated  by  the  formula  on  page  26. 
Taking  the  temperature  of  the  air  supply  at  62°  and  that  of  the 
escaping  chimney-gases  at  462°,  this  loss  is  810  B.T.U.,  which  sub- 
tracted from  5824  gives  5014  B.T.U.  per  pound  as  the  available  heat- 
ing value. 

Sawdust. — The  heating  power  of  sawdust  is  naturally  the  same 
per  pound  as  that  of  the  wood  from  which  it  is  derived,  but  if  allowed 
to  get  wet  it  is  more  like  spent  tan  (which  see  below).  The  con- 
ditions necessary  for  burning  sawdust  are  that  plenty  of  room  should 
be  given  it  in  the  furnace,  and  sufficient  air  supplied  on  the  surface 
of  the  mass.  The  same  applies  to  shavings,  refuse  lumber,  etc.  Saw- 
dust is  frequently  burned  in  sawmills,  etc.,  by  being  thrown  into  the 
furnace  by  a  fan-blast. 


176  STEAM-BOILER  ECONOMY. 

Wet  Tan-bark. — Tan,  or  oak-bark,  after  having  been  used  in  the 
processes  of  tanning,  is  burned  for  fuel.  The  spent  tan  consists  of 
the  fibrous  portion  of  the  bark.  According  to  M.  Peclet,  five  parts  of 
oak-bark  produce  four  parts  of  dry  tan;  and  the  heating  power  of 
perfectly  dry  tan,  containing  15%  of  ash,  is  6100  British  thermal 
units;  whilst  that  of  tan  in  an  ordinary  state  of  dryness,  containing 
30%  of  water,  is  only  4284  B.T.U.* 

The  principal  cause  of  poor  economy  in  the  burning  of  tan  bark, 
besides  the  difficulty  of  securing  good  combustion  in  the  furnace,  is 
the  amount  of  heat  that  is  carried  away  in  the  shape  of  superheated 
steam  in  the  chimney  gases.  If  the  bark,  after  being  partly  dried 
by  compression,  were  further  dried  in  a  rotary  drier  by  the  waste 
heat  from  the  chimney  gases,  there  would  be  a  very  important  gain  in 
economy.  The  following  calculation  shows  the  theoretical  results  that 
may  be  obtained  in  burning  tan  bark  of  different  degrees  of  moisture 
under  certain  assumed  conditions.  The  dry  bark  is  assumed  to  have 
the  composition  C  =  0.50;  H  =  0.06;  0  =  0.40;  N  and  ash 
=  0.04.  Heating  value  by  Dulong's  formula  7920  B.T.TL  per  ib. 
Bark  containing  20  per  cent  moisture  would  have  a  heating  value  of 
0.80  X  7920  =  6336  B.  T.  U. 

Assuming  the  chimney  gases  to  escape  at  600°,  the  heat  required 
to  evaporate  1  Ib.  water  from  62°,  and  to  superheat  the  steam  to  600 
would  be  (212  —  62)  +  970  +  0.48  (600  —  212)  =  1306,  or  for  20 
per  cent  moisture,  261  B.  T.  U.  per  pound  of  tan. 

The  0.06  Ib.  of  H  in  a  pound  of  dry  tan  will  unite  with  0.06  X 
8  =*  0.48  0,  making  0.54  Ib.  H20,  which  escapes  as  superheated 
steam,  carrying  away  0.54  X  1306  =  705  B.  T.  U.  for  each  pound 
of  dry  tan  or  0.80  X  705  =  564  B.  T.  U.  for  tan  with  20  per  cent 
moisture. 

Assuming  25  Ib.  of  air  to  be  required  per  Ib.  of  C  +  H  in 
the  fuel  or  25  X  0.56  =  14  Ib.  of  dry  tan,  the  heat  carried  away  by 
this  air  heated  to  600°  is  0.24  X  14  X.  (600  —  62)  =  1808  B.T.U. 
per  Ib.  of  dry  tan  or  1446  B.T.U.  for  tan  with  20  per  cent  moisture. 
Using  the  figures  thus  found  the  following  table  is  constructed : 


*  David  Moffatt  Myers  (Trans.  A.S.M.E.,  1909,)  gives  the  average  heating 
value  of  dry  hemlock  tan,  as  found  by  a  bomb  calorimeter  in  six  tests  by 
Dr.  Sherman,  as  9504  B.T.U.  The  composition  of  dry  tan  is  ash,  1.42;  C,  51.80; 
H,  6.04;  O,  40.74.  By  Dulong's  formula  the  heating  value  would  be  8152 
B.T.U. 


FUELS  OTHER  THAN  COAL. 


Ill 


Mois- 
ture. 

B.T.U. 
per  Ib. 
Wet 

Losses  of  Heat  Due  to 

Net  Heat 
Value, 
B.T.U. 

! 

Efficiency, 
Per  Cent. 

Lb.  Evap. 
per  Ib. 
Wet  Tan. 

Tan. 

Moisture. 

H  in  Fuel. 

Heating  Air. 

0.20 

6336 

261 

564 

1446 

4065 

64.2 

4.19 

0.30 

5544 

392 

493 

1266 

3393 

61.2 

3.50 

0.40 

4752 

522 

423 

1085 

2772 

57.3 

2.81 

0.50 

3960 

653 

352 

904 

2051 

51.8 

2.11 

0.60 

3168 

784 

282 

723 

1379 

43.5 

1.42 

0.70 

2376 

914 

211 

542 

709 

29.8 

0.73 

0.80 

1584 

1045 

141 

362 

36 

2.5 

0.03 

Suppose  that  tan  with  60  per  cent  moisture  were  dried  to  20 
per  cent  before  being  put  into  the  furnace,  using  for  this  purpose  the 
waste  heat  of  the  chimney  gases,  we  would  then  have  0.40  dry  tan  + 
0.60  moisture  dried  to  0.40  dry  tan  +  0.10  moisture,  0.50  water  being 
removed.  If  the  moisture  and  the  waste  gases  left  the  drying 
chamber  at  300°  then  each  pound  of  moisture  would  take  (212  —  62) 
+  970  +  0.48(300-212)  =1162  B.T.U.  and  0.6  Ib.  would  take 
697  B.  T.  U.-  The  H  in  the  0.40  Ib.  of  dry  tan  would  make  0.216 
H20,  which  would  take  away  0,216  X  1162  ==  251  B.  T.  U.  Heat- 
ing the  air  would  take  0.40  X  14  X  0.24  X  (300  --  62)  =  320 
B.  T.  U.  The  sum  of  these  is  1268,  which  subtracted  from  3168, 
the  total  heating  value  of  tan  with  60  p.er  cent  moisture,  leaves  a  net 
value  of  1900  instead  of  1379,  the  figure  given  in  the  table.  The 
efficiency  would  be  1900  -+-  3168  =  60.0  per  cent,  instead  of  43.5 
per  cent,  and  the  evaporation  from  and  at  212°  1900  -i-  970  =  1.96 
Ibs.  instead  of  1.42  Ibs. 

Straw  as  Fuel. — Experiments  in  Eussia  showed  that  winter-wheat 
straw,  dried  at  230°F.,  had  the  following  composition".  C,  46.1;  H, 
5.6;  N,  0.42;  0,  43.7;  Ash,  4.1.  Heating  value  in  British  thermal 
units:  dry  straw,  6290;  with  10%  water,  5448.  With  straws  of  other 
grains  the  heating  value  of  dry  straw  ranged  from  5590  for  buck- 
wheat to  6750  for  flax.* 

Clark  ("Steam-engine,"  vol.  i,  p.  62)  gives  the  mean  composition 
of  wheat  and  barley  straw  as  C,  36;  H,  5;  0,  38;  N",  0.50;  Ash, 
4.75;  water,  15.75,  the  two  straws  varying  less  than  1%.  The  total 
heating  value  of  straw  of  this  composition,  according  to  Dulong's 
formula,  is  5411  heat-units.  Clark  erroneously  gives  it  as  8144  heat- 
units.  Taking  the  temperature  of  the  chimney-gases  at  462°  and 


*Eng.  Mechanics,  Feb.,  1893,  p.  55. 


178  STEAM-BOILER  ECONOMY. 

that  of  the  air-supply  at  62°  the  "available"  heating  value  is  4660 
B.T.U. 

Bagasse  as  Fuel  in  Sugar  Manufacture. — Bagasse  is  the  name 
given  to  refuse  sugar-cane,  after  the  juice  has  been  extracted.  Prof. 
L.  A.  Becuel,  in  a  paper  read  before  the  Louisiana  Sugar  Chemists' 
Association,  in  1892,  says:  "With  tropical  cane  containing  12.5% 
woody  fibre,  a  juice  containing  16.13%  solids,  and  83.87%  water, 
bagasse  of,  say,  66%  and  72%  mill  extraction  would  have  the  follow- 
ing percentage  composition : 


Woody  Fibre. 

Combustible 
Salts. 

Water. 

66%  bagasse  
72%  bagasse  

37 

45 

10 
9 

53 

46 

"Assuming  that  the  woody  fibre  contains  51%  carbon,  the  sugar 
and  other  combustible  matters  an  average  of  42.1%,  and  that  12,906 
units  of  heat  are  generated  for  every  pound  of  carbon  consumed,  the 
66%  bagasse  is  capable  of  generating  2978  heat-units  per  pound  as 
against  3452,  or  a  difference  of  474  units  in  favor  of  the  72%  bagasse. 

"Assuming  the  temperature  of  the  waste  gases  to  be  450°  F.,  that 
of  the  surrounding  atmosphere  and  water  in  the  bagasse  at  86°  F., 
and  the  quantity  of  air  necessary  for  the  combustion  of  one  pound  of 
carbon  at  24  Ibs.,  the  lost  heat  will  be  as  follows :  In  the  waste  gases, 
heating  air  from  86°  to  450°  F.,  and  in  vaporizing  the  moisture,  etc., 
the  66%  bagasse  will  require  1125,  and  the  72%  bagasse  1161  heat- 
units. 

"  Subtracting  these  quantities  from  the  above,  we  find  that  the 
66%  bagasse  will  produce  1853  available  heat-units,  or  nearly  38% 
less  than  the  72%  bagasse,  which  gives  2990  units. 

"It  appears  that  with  the  best  boiler  plants,  those  taking  up  all 
the  available  heat  generated,  by  using  this  heat  economically  the 
bagasse  can  be  made  to  supply  all  the  fuel  required  by  our  sugar- 
houses/' 

The  figures  given  below  are  taken  from  an  article  by  Samuel 
Vickess  (The  Engineer,  Chicago,  April  1,  1903). 

When  canes  with  12  per  cent  fiber  are  ground,  the  juice  extractions 
and  liquid  left  in  the  residual  bagasse  are  generally  as  shown  in  the 
following  table: 


FUELS  OTHER  THAN  COAL. 


179 


With 

Per  Cent  of  Normal 
Juice  Extracted  on 
Weight  of  Cane. 

Per  Cent  of  Liquid 
Left  in  Bagasse  on 
Weight  of  Bagasse. 

Double  crushing 

70 

60 

Single  crushing 

62 

68 

Crusher  and  double  crushing 

72 

57 

Triple  crushing  

76 

50 

Crusher  and  triple  crushing  with  saturation 

82 

50 

The  value  of  bagasse  as  a  fuel  depends  upon  the  amount  of  woody 
fiber  it  contains,  and  the  amount  of  combustible  matter  (sucrose, 
glucose,  and  gums),  held  in  the  liquid  it  retains.  100  Ibs.  cane  with 
triple  crushing  gives  76  Ibs.  juice,  and  24  Ibs.  bagasse,  which  consists 
of  12  Ibs.  fiber  and  12  Ibs.  juice.  The  12  Ibs.  of  juice  contains  16  per 
cent  or  1.92  Ibs.  sucrose,  0.5  per  cent  or  0.06  Ib.  glucose,  2.5  per  cent 
other  organic  matter  and  1  per  cent  or  0.12  Ib.  ash,  making  a  total  of 
20  per  cent  or  2.4  Ibs.  of  solid  matter,  and  80  per  cent  or  9.6  Ibs.  of 
water.  Reducing  these  figures  to  quantities  corresponding  to  1  Ib. 
of  bagasse,  and  multiplying  by  the  heating  values  of  the  several  sub- 
stances as  given  by  Stohlmann,  we  find  the  heating  value  of  the  com- 
bustible in  1  Ib.  of  bagasse  as  follows : 

0.5       Ib.  fiber  X 7461  =3730  B.T.U. 

0.08  Ib.  sucrose  X6957=  557  " 
0. 0025  Ib.  glucose  X6646  =  17  " 
0.0125  Ib.  org.  matter X 7461  =93  " 


0.4 
0.005 

1.0000 


Ib.  water 
Ib.  ash 


4397 


This  4397  B.  T.  U.  is  the  gross  heating  value,  which  would  be 
obtained  in  a  calorimeter  in  which  the  products  of  combustion  were 
cooled  to  the  temperature  of  the  atmosphere.  To  find  approximately 
the  heat  available  for  generating  steam  in  a  boiler  we  may  assume 
that  10  Ibs.  of  air  is  used  in  burning  each  pound  of  bagasse,  that  the 
atmospheric  temperature  is  82°  and  the  flue  gas  temperature  462°, 
and  that  in  addition  to  the  0.4  Ib.  water  per  Ib.  bagasse  one-half  of  the 
remaining  0.6  Ib.  is  oxygen  and  hydrogen  in  proportions  which  form 
water,  making  0.7  Ib.  water  which  escapes  in  the  flue  gas  as  super- 
heated steam.  The  heat  lost  in  the  flue  gases  per  pound  of 
is  [  10  X  0.24  X  (462  —  82)  +  0.7  (212  —  82)  +  970 


180  STEAM-BOILER  ECONOMY. 

_|_0.5  (462  — 212)]  =  1770  B.T.U.,  which  subtracted  from  4397 
leaves  2627  B.  T.  U.  as  the  net  or  available  heating  value,  which  is 
equivalent  to  an  evaporation  of  2.7  Ibs.  of  water  from  and  at  212°. 
Mr.  Vickess  states  that  in  practice  I  Ib.  of  such  green  bagasse  evaporates 
2  to  21/4  Ibs.  from  feed  water  at  100°  into  steam  at  90  Ibs.  pressure. 
This  is  equivalent  to  from  2.31  to  2.59  Ibs.  from  and  at  212°. 

Drying  Bagasse  with  the  Waste  Heat  from  Boilers. — Prof.  E.  W. 
Kerr,  in  Bulletin  No.  128  of  the  Agricultural  Experiment  Station 
of  the  Louisiana  State  University,  1911,  describes  a  series  of  about 
40  boiler  tests,  some  with  wet  bagasse  and  some  with  bagasse  that  had 
been  partially  dried  by  contact  with  boiler  flue  gases  in  an  experi- 
mental drying  apparatus.  It  was  found  that  there  was  no  danger 
of  setting  the  bagasse  on  fire  in  the  drier  as  long  as  it  was  kept  moving. 
The  average  temperature  of  the  gases  entering  the  drier  was  474°  F., 
and  that  leaving  the  drier,  219°.  The  principal  conclusions  of  the 
paper  are  as  follows: 

For  bagasse  with  52%  moisture,  which  is  not  far  from  the  average 
in  Louisiana,  16%  of  the  heat  generated  is  required  to  evaporate  the 
moisture  in  the  bagasse  and  raise  its  temperature  to  that  of  the  stack. 

The  heat  wasted  in  the  stack  gases  varies  with  the  efficiency  of 
the  boiler  and  furnace.  Theoretically,  the  heat  thus  wasted  is  more 
than  sufficient  to  evaporate  all  the  moisture  from  the  bagasse  by  the 
use  of  an  efficient  dryer.  With  bagasse  having  52%  moisture  and  a 
boiler  having  60%  efficiency,  the  efficiency  of  the  drier  would  have 
to  be  only  60%  in  order  to  remove  all  of  the  moisture  from  the  bagasse. 

The  average  moisture  in  the  bagasse  entering  the  drier  was  54.3%, 
and,  leaving  it,  46.4%,  which  means  that  14.5%  of  the  moisture  in 
the  bagasse  was  removed  by  the  drying  process. 

The  average  equivalent  evaporation  from  and  at  212°  F.  per  Ib.  of 
wet  bagasse  burned  was  1.63  Ibs.  and  that  for  the  partially  dried 
bagasse,  2.53  Ibs.  One  pound  of  the  partially  dried  bagasse  had  a 
heat  value  of  55.2%  greater  than  that  of  1  Ib  of  wet  bagasse. 

The  average  boiler  efficiency  for  the  tests  with  the  drier  in  use 
was  63.5%  and  that  with  undried  bagasse,  50.7%.  The  increased 
efficiency  with  partially  dried  bagasse  is  probably  due  to  less  smolder- 
ing during  combustion  and  to  higher  furnace  temperatures. 

Based  on  an  equivalent  evaporation  of  14  pounds  of  water  from 
and  at  212°  per  pound  of  oil,  the  saving  due  to  drying  was  calculated 
to  be  2.57  gallons  of  oil  per  ton  of  cane.  For  a  grinding  of  60,000 
tons  this  would  give  a  total  saving  of  3673  barrels  of  oil. 

Petroleum. — Thos.  Urquhart  of  Russia  gives  the  following  table 
of  the  theoretical  evaporative  power  of  petroleum  in  comparison  with 
that  of  coal,  as  determined  by  Messrs.  Favre  and  Silbermann  :* 

*  Proc.  Inst.  M.  E.  Jan.,  1889. 


FUELS  OTHER  THAN  COAL. 


181 


TTnpl 

Specific 
Gravity 

Chem.  Comp. 

Heating 
power, 

Theoret. 
Evap.,  Ibs. 
Water  per 

Water 
=  1.000. 

C. 

% 

H. 

% 

0. 

% 

Thermal 
Units. 

Ib.  Fuel, 
from  and 
at  212°  F. 

Penna.  heavy  crude  oil  .  . 

0.886 

84.9 

13.7 

1.4 

20,736 

21.48 

Caucasian  light  crude  oil. 
heavy       "     . 

0.884 
0.938 

86.3 
86.6 

13.6 
12.3 

0.1 
1.1 

22,027 
20,138 

22.70 
20.85 

Russian  naphtha  refuse.  . 
Good  English  coal,  mean 

0.928 

87.1 

11.7 

1.2 

19,832 

20.53 

of  98  samples      

1.380 

80.0 

5.0 

8.0 

14,112 

14.61 

In  experiments  on  Russian  railways  with  petroleum  as  fuel,  Mr. 
Urquhart  obtained  an  actual  efficiency  equal  to  82%  of  the  theoretical 
heating  value.  The  petroleum  is  fed  to  the  furnace  by  means  of  a 
spray-injector  driven  by  steam.  An  induced  current  of  air  is  car- 
ried in  around  the  injector-nozzle,  and  additional  air  is  supplied  at 
the  bottom  of  the  furnace. 

The  following  notes  are  condensed  from  a  paper  on  "Crude  Petro- 
leum and  its  Products  as  Fuel,"  by  E.  H.  Tweddle.* 

Crude  petroleum  is  a  hydrocarbon,  often  containing  a  small  per- 
centage of  sulphur  and  oxygen  as  impurities.  Its  specific  gravity  may 
vary  from  12°  to  70°  Baume,  but  the  greatest  quantity  produced 
ranges  from  30°  to  45°  Baume.  The  color  of  crude  petroleum  is 
usually  a  green  brown,  but  it  is  found  from  a  light  brown  color, 
through  the  various  shades  of  green  to  a  jet  black.  It  may  be  broken 
up  by  distillation  into  benzene,  kerosene,  and  other  distillates  and 
residuums  of  various  qualities,  any  one  of  which  makes  a  very  good 
fuel  under  certain  conditions. 

Gasolene,  or  petroleum  distillate  of  more  than  74°  Baume,  will 
never  be  used  for  fuel  except  to  a  very  limited  extent,  since  it  and 
its  closely  associated  distillates  are  always  more  valuable  for  other 
purposes.  [It  is  extensively  used  in  internal  combustion  engines.] 

Benzene,  or  petroleum  distillate  from  55°  to  74°  Baume,  is* the 
best  of  all  liquid  fuels,  but  its  use  is  restricted  owing  to  the  care  with 
which  it  has  to  be  handled.  The  difficulty,  danger  and  expense  of 
transporting  will  only  allow  of  its  use  in  a  very  few  favored  localities. 

Kerosene  or  petroleum  distillate  of  from  48°  B  to  35°  B  gravity 
is  an  excellent  fuel,  but,  owing  to  the  expense  attending  its  prepara- 
tion, we  can  hardly  expect  to  see  the  price  fall  below  3c.  per  gallon, 


*  Engineering  and  Mining  Journal,  Oct.  14,  21,  and  28,  1899. 


182  STEAM-BOILER  ECONOMY. 

except  in  the  places  where  it  is  produced;  for,  should  it  generally 
become  so  cheap  the  consumption  of  it  as  an  illuminant  would  in^ 
crease  so  enormously  that  there  would  be  little  left  for  fuel. 

The  present  price  of  kerosene  in  bulk  and  in  large  quantity  may 
be  taken  at  about  3c.  per  gallon  at  its  place  of  production,  both  in 
Russia  and  America.  As  a  fuel  for  small  boilers  it  is  the  best,  because 
of  its  portability  and  the  safety  and  facility  with  which  it  can  be 
handled. 

Next  to  kerosene,  some  of  the  heavy  distillates  of  petroleum  known 
as  neutral  or  solar  oils  could  be  used  as  fuel,  but  they  have  no  par- 
ticular advantage  over  kerosene,  save  their  high  fire-test. 

Crude  petroleum  may  contain  any  portion  of  benzene  and  kerosene 
from  nothing  up  to  nearly  90  per  cent,  varying  entirely  with  the 
locality  where  it  is  produced.  We  may  say  roughly  that  of  these  two 
distillates,  American  crude  petroleum  contains  50  to  75  per  cent  of 
kerosene  and  benzene;  Russian  from  15  to  50  per  cent;  Peruvian  from 
15  to  50  per  cent. 

If  distillation  is  stopped  after  the  benzenes  and  kerosenes  have 
been  run  off,  there  remains  in  the  still  an  oil  known  by  the  various 
names  of  residuum,  reduced  oil,  tar,  fuel-oil,  astatki,  mazoot,  petro- 
leum refuse,  etc. 

If  the  distillation  of  this  residuum  is  pushed  still  farther, 
neutral  and  lubricating  oils  distill  over,  or  else,  with  certain  forms 
of  stills,  decomposition  sets  in,  and  various  products  may  be  dis- 
tilled over,  until  nothing  but  a  small  amount  of  coke  is  left  in  the 
still. 

The  demand  for  mineral  lubricating  oils  is  so  great  in  the  United 
States  that  but  little  residuum  would  be  placed  on  the  market  at  a 
price  which  would  render  it  available  as  a  fuel-oil.  In  Russia,  how- 
ever, where  the  crude  oil  contains  a  low  percentage  of  kerosene,  there 
is  an  enormous  surplus  of  residuum,  which  cannot  all  be  used  for  the 
manufacture  of  lubricating  oils.  It  is  generally  known  as  "astatki" 
or  "mazoot,"  and  is  used  for  fuel  in  all  possible  places.  This  astatki 
is  the  fuel-oil  par  excellence  for  marine  and  locomotive  work  where 
a  perfectly  safe  oil  is  required.  It  is  now  distributed  largely  over 
the  Russian  Empire,  and  in  1890  some  600,000  tons  were  used  for 
interior  navigation  in  Russia  alone,  and  the  consumption  has  been 
constantly  increasing. 

The  eastern  petroleum  region  of  the  United  States  is  about  400 
miles  from  the  seaboard,  and  although  many  pipe-lines  traverse  this 


FUELS  OTHER   THAN  COAL.  183 

distance,  there  must  be  an  expense  connected  with  the  carriage  of  the 
crude  oil.  The  petroleum  fuel  consumed  in  the  United  States  is 
almost  restricted  to  the  use  of  crude  oil,  and  this  is  not  the  fuel 
which  will  suit  the  general  consumer,  especially  if  he  is  to  use  the 
oil  for  either  railroad  or  marine  purposes.  Crude  oil  is  a  most  ex- 
cellent and  easily  handled  fuel,  but  it  must  be  used  with  caution, 
and  is  absolutely  unfit  for  use  on  a  locomotive  or  steamer,  since,  in 
case  of  accident,  it  may  catch  fire  and  spread  with  startling  rapidity. 
For  such  purposes  no  petroleum  should  be  used  that  has  a  fire-test 
of  less  than  200°  to  250°  Fahrenheit.  A  petroleum  oil  with  a  fire- 
test  of  250°  F.  is  a  safer  fuel  than  coal. 

Eesiduum  oil  which  has  a  fire-test  of  say  250°  to  300°  F.  is  the 
most  suitable  for  fuel  on  steamers,  since  it  is  absolutely  safe,  as  it 
cannot  take  fire  and  does  not  give  off  inflammable  gases  until  heated 
to  a  temperature  above  that  of  boiling  water.  As  the  fuel  would  be 
carried  in  tanks  below  the  water-line,  heating  to  that  degree  becomes 
a  practical  impossibility.  Such  oil  may  be  placed  in  a  bucket  and 
stirred  with  a  red-hot  poker  without  catching  fire;  shovelfuls  of 
hot  coals  may  be  thrown  into  it,  but  they  will  sink  and  be  extin- 
guished the  same  as  if  thrown  in  water. 

It  is  probable  that  in  the  future  petroleum  fuel  will  be  used  more 
for  marine  purposes  on  account  of  economy  in  space  and  weight. 
California  petroleum  will  probably*  be  largely  used  for  this  purpose, 
as  the  production  of  crude  petroleum  there  is  being  rapidly  increased, 
and  the  oil  is  better  suited  by  its  quality  for  fuel  than  for  refining 
purposes,  owing  to  the  small  proportion  of  volatile  constituents  and 
large  proportion  of  heavy  hydrocarbons.  It  is  just  the  contrary  with 
the  petroleum  found  in  the  Eastern  States,  which  is  especially 
adapted  to  the  manufacture  of  illuminating  oils,  owing  to  the  large 
proportion  of  volatile  hydrocarbons  it  contains. 

The  petroleum-fields  of  Peru  somewhat  resemble  those  of  Cali- 
fornia, and  are  most  favorably  situated  close  to  the  sea,  The  crude 
oil  is  a  good  fuel  for  stationary  boilers,  and,  if  40  per  cent  of  ben- 
zene and 'kerosene  are  distilled  off,  the  resulting  residuum  is  an  oil 
of  about  22°  B.  gravity  and  260°  to  280°  fire-test,  of  moderate  vis- 
cosity and  containing  no  paraffine.  It  preserves  its  fluidity  at  low 
temperatures,  and  makes  an  excellent  fuel  for  either  locomotive  or 
marine  use.  The  price  at  which  it  can  be  supplied  is  $5.00  to  $7.50 
per  ton.  As  good  coal  on  the  west  coast  of  South  America  seldom 
reaches  a  lower  figure*  than  $6.25  per  ton,  this  fuel-oil  will  be  able  to 


184  STEAM-BOILER  ECONOMY.    . 

compete   with   it   from   an   economic  point    of   view   as   soon   as   a 
sufficiently  large  supply  of  it  is  guaranteed. 

Some  of  the  advantages  claimed  for  liquid  fuel  are: 

1.  Diminished  loss  of  heat  up  the  funnel,  owing  to  the  clean  con- 
dition the  tubes  can  be  kept  in,  and  to  the  smaller  amount  of  air 
which  has  to  pass  through  the  combustion-chamber  for  a  given  fuel 
consumption. 

2.  A  more  equal  distribution  of  heat  in  the  combustion-chamber, 
as  the  doors  do  not  have  to  be  opened,  and  consequently  a  higher 
efficiency  is  obtained. 

3.  With  oil  there  is  no  chance  of  getting  dirty  fires  on  a  hard  run, 
as  with  coal. 

4.  A  reduction  in  cost  of  handling  fuel,  since  in  one  case  it  is  ail 
done  mechanically  or  by  gravitation,  while  with  solid  fuel  a  great 
deal  of  manual  labor  is  required. 

5.  No  firing  tools  or  grate-bars  are  used,  consequently  the  furnace 
lining  and  brickwork  floors,  etc.,  suffer  less  damage. 

6.  No  dust  nor  ashes  to  cover  or  fill  the  tubes  and  diminish  the 
heating  surface,  nor  to  be  handled  or  carted  away. 

7.  Petroleum  does  not  suffer  while  being  stored,  while  the  dete- 
rioration of  coal  under  atmospheric  influence  is  well  known. 

8.  Ease  with  which  fire  can  be  regulated,  from  a  low  to  a  most 
intense  heat  in  a  short  time. 

9.  Absence   of   sulphur   or   other   impurities   and   longer   life   of 
plates,  etc. 

10.  Lessening  of  manual  labor  to  fireman. 

11.  Great    increase    of    steaming    capacity,    as   was    conclusively* 
proved  when  many  factories  returned  to  coal  in  Pennsylvania  and 
Ohio;  they  had  to  increase  their  boiler  capacity  about  35  per  cent. 

The  coal  consumption  of  the  world  is  probably  in  the  neighbor- 
hood of  600,000,000  tons  per  annum,  while  that  of  petroleum  is  only 
about  17,000,000  tons,  of  which  by  far  the  greatest  part  is  used  for 
illuminating  or  lubricating  purposes;  so  the  amount  of  petroleum 
available  for  fuel  purposes  is  probably  not  more  than  1  per  cent  of 
the  coal  used.*  Liquid  fuel  will  therefore  never  be  used  very  ex- 

*  These  figures  are  for  1899.  In  1912,  according  to  the  reports  of  the  U.  S. 
Geological  Survey,  the  total  coal  production  of  the  United  States  alone  was, 
in  round  figures,  716,920,000  tons  of  2000  Ibs.,  and  that  of  petroleum,  taking 
330  Ibs.  as  the  weight  of  a  barrel  of  42  gallons,  36,650,000  tons,  or  a  trifle  over 
5  per  cent  of  the  coal  production. 


FUELS  OTHER  THAN  COAL. 


185 


tensively  as  compared  with  coal,  but  where  it  is  used  it  will  have 
many  advantages  over  the  solid  fuel.  On  vessels  of  war,  and 
especially  torpedo-boats,  it  would  give  the  very  best  results  if  used 
intelligently. 

Calorific  Values  of  California  Fuel  Oils. — E.  W.  Fenn,  in 
Engineering  News,  May  13,  1909,  gives  the  following  table  showing 
that  the  heating  value  of  fuel  oil  has  a  direct  relation  to  its  density: 


Deg. 
Baume. 

Specific 
Gravity. 

Weight 
per  bbl. 

B.T.U. 
per  Ib. 

Thous- 
ands 
B.T.U. 
per  bbi. 

Deg. 
Baume. 

Specific 
Gravity. 

Weight 
per  bbl. 

B.T.U. 
per  Ib. 

Thous- 
ands 
B.T.U. 
per  bbl. 

10° 

1.000 

350 

18,380 

6442 

28° 

0.887 

311 

19,460 

6051 

11 

0.993 

348 

18,440 

6418 

29 

0.881 

309 

19,520 

6030 

12 

0.986 

346 

18,500 

6394 

30 

0.875 

307 

19,580 

6008 

13 

0.979 

343 

18,560 

6370 

31 

0.870 

305 

19,640 

5990 

14 

0.972 

341 

18,620 

6345 

32 

0.865 

303 

19,700 

5973 

15 

0.966 

339 

18,680 

6323 

33 

0.860 

301 

19,760 

5954 

16 

0.959 

336 

18,740 

6302 

34 

0.854 

299 

19,820 

5935 

17 

0.953 

334 

18,800 

6280 

35 

0.849 

298 

19,880 

5917 

18 

0.947 

332 

18,860 

6257 

36 

0.844 

296 

19,940 

5901 

19 

0.940 

330 

18,920 

6235 

37 

0.839 

294 

20,000 

5885 

20 

0.934 

327 

18,980 

6212 

38 

0.835 

293 

20,050 

5865 

21 

0.928 

325 

19,040 

6193 

39 

0.830 

291 

20,100 

5846 

22 

0.922 

323 

19,100 

6173 

40 

0.825 

289 

20,150 

5827 

23 

0.916 

321 

19,160 

6153 

41 

0.820 

288 

20,200 

5808 

24 

0.910 

319 

19,220 

6133 

42 

0.816 

286 

20,250 

5789 

25 

0.905 

317 

19,280 

6113 

43 

0.811 

284 

20,300 

5770 

26 

0.899 

315 

19,340 

6093 

44 

0.806 

283 

20,350 

5751 

27 

0.893 

313 

19,400 

6072 

45 

0.802 

281 

20,400 

5732 

From  these  figures  it  appears  that  the  thinner  the  crude  oil  the 
higher  is  its  heating  value  per  pound  but  the  less  per  barrel. 

The  following  table   shows  the  world's  production  for   1911   in 


Country. 

Rank. 

Bbls. 

Metric 
Tons. 

Total 

% 

United  States  
Russia  

1 

2 

220,449,391 
66,183,691 

29,393,252 
9,066,259 

63.80 
19.16 

Mexico 

3 

14,051,643 

1,873,552 

4.07 

Dutch  East  Indies. 

4 

12,172,949 

1,670,668 

3.52 

Roumania                          

5 

11,101,878 

1,544,072 

3.21 

Galicia.        

6 

10,485,726 

1,458,275 

3.04 

India  

7 

6,451,203 

897,184 

1.87 

Japan 

8 

1,658,903 

221,187 

.48 

Peru                                  .    . 

9 

1,398,036 

186,405 

.40 

Germany. 

10 

995,764 

140,000 

.29 

Canada            ...            ... 

11 

291,096 

38,813 

.08 

Italy  

12 

*71,905 

10,000 

.02 

Other  

*  200,000 

26,667 

.06 

Total 

345,512,185 

46,526,334 

100.00 

*Estimated. 


186 


STEAM-BOILER  ECONOMY. 


barrels  and  metric  tons  ("Mineral  Kesources,"  U.  S.  Geological  Sur- 
vey). 

Pr6perties  of  California  Crude  Oils. —  (F.  S.  Wade,  Power,  Nov. 
14,  1911.)  A  table  is  given  showing  a  great  variation  in  the  density 
and  heating  value  of  oils  obtained  from  different  districts.  The 
density  ranges  from  0.854  sp.  gr.  —  34  degrees  Baume  —  7.12  Ibs. 
per  gallon  to  0.988  sp.  gr.  =  11.7  Baume  =  8.24  Ibs.  per  gal.  The 
sulphur  ranges  from  0.32  to  4.43%,  and  the  B.T.U.  per  Ib.  from 
19,400  B.T.U.  per  Ib.  for  the  lightest  oils  down  to  18,480  for  the 
heaviest.  These  figures  are  for  oil  entirely  free  from  moisture.  The 
B.T.U.  per  pint  of  the  lightest  oil  is  17,270,  and  that  of  the  heaviest 
oil  19,030. 

The  variations  in  the  calorific  value  of  oils  of  apparently  the  same 
gravity  are  often  found  and  are  due  to  water  in  the  oil,  which  in 
many  cases  is  undetected  and  not  corrected  for  on  account  of  the 
rather  general  use  of  the  so-called  "gasolene  test"  for  water.  This 
test  is  made  by  mixing  equal  portions  of  gasolene  and  oil  and  allowing 
the  mixture  to  stand  24  hours.  At  the  end  of  this  time  the  per- 
centage of  water  can,  supposedly,  be  read  off  on  a  scale  at  the  bottom 
of  the  test  cylinder.  This  test  rarely  with  any  oil,  and  almost  never 
with  the  heavier  oils,  reveals  the  full  and  correct  amount  of  water 
present.  In  the  experience  of  the  writer,  water  in  crude  oil  can  be 
determined  satisfactorily  only  by  the  use  of  a  high-speed  centrifugal 
testing  machine  or  by  distillation. 

It  is  often  necessary  to  correct  the  gravity  or  volume  of  fuel  oil 
for  temperature.  Repeated  experiment  has  proved  that  the  expan- 
sion factors  of  California  oils  between  12  and  22  degrees  Baume  is 
substantially  0.0004  per  degree  Fahrenheit,  which  gives  a  correction 
in  gravity  of  0.06  degrees  Baume  for  each  degree  Fahrenheit  of  the 
oil  above  or  below  60°. 

The  accompanying  table  (from  Power}  gives  what  may  be  con- 
sidered representative  figures  for  the  composition,  weights  and  heat 
values  of  American  oils: 

PROPERTIES    OF    CRUDE    OILS. 


Kind  of  Oil. 

Composition  by  Weight. 

Specific 
Gravity. 

Pounds 
per 
Gallon. 

B.T.U.  per  Pound. 

Carbon. 

Hydro- 
gen. 

Sul- 
phur. 

Oxy- 
gen. 

By  Test. 

Com- 
puted. 

Ohio  

0.834 
0.820 
0.349 
0.843 
0.835 
0.840 
0.852 

0.147 
0.148 
0.137 
0.141 
0.133 
0.132 
0.124 

0.006 
0.010 

6!  003 
0.008 
0.010 
0.005 

0.013 
0.022 
0.014 
0.013 
0.024 
0.018 
0.019 

0.800 
0.816 
0.886 
0.841 
0.873 
0.925 
0.959 

6.68 
6.80 
7.40 
7.02 
7.28 
7.71 
8.00 

19,580 
19,930 
19,210 
18,400 
18,324 
19,100 
18,500 

19,718 
19,519 
19,385 
18,527 
18,860 
18,928 
18,656 

Pennsylvania,  light.  . 
Pennsylvania,  heavy  . 
West  Virginia,  light  .  . 
West  Virginia,  heavy. 
Texas 

Average.  ....... 

0.839 

0.139 

0.007 

0.018 

0.871 

7.27 

19,006 

19,086 

The  formula  by  which  the  computed  results  were  obtained  is  not  given. 


FUELS  OTHER   THAN  COAL. 


187 


Other  figures  for  the  heating  value  of  oils  are  given  below: 

Redondo,  Cal.,  oil,  six  lots:  Moisture,  1.82  to  2.70  per  cent; 
sulphur,  2.17  to  2.60  per  cent;  B.  T.  U.  per  lb.,  17,717  to  17,966. 
Kilowatt-hours  generated  per  barrel  (334  Ibs.)  of  oil  in  a  5000  K.  W. 
plant,  using  water-tube  boilers,  and  reciprocating  engines  and  gen- 
erators having  a  combined  efficiency  of  90.2  to  94.75  per  cent  (boiler 
economy  and  steam-rate  of  engine  not  stated).  2000  K.  W.  load, 
237.3;  3000  K.  W.,  256.7;  5000  K.  W.,  253.4;  variable  load,  24  hours, 
243.8.  (C.  R.  Weymouth,  Trans.  A.  S.  M.  E.,  1908.) 

Beaumont,  Texas,  oil  analyzed  as  follows  (Eng.  News,  Jan.  30, 
1902):  C,  84.60;  H,  10.90;  S.  1.63;  0,  2.87.  Sp.  gr.,  0.92;  flash 
point,  142°  F. ;  burning  point,  181°  F. ;  heating  value  per  lb.,  by 
oxygen  calorimeter,  19,060  B.  T.  U.  A  test  of  a  horizontal  tubular 
boiler  with  this  oil,  by  J.  E.  Denton  gave  an  efficiency  of  78.5  per 
cent.  As  high  as  82  per  cent  has  been  reported  for  California  oil. 

Bakersfield,  Cal.,  oil:  Sp.  gr.  16°  Baume;  moisture,  1  per  cent; 
sulphur,  0.5  per  cent;  B.  T.  U.  per  lb.,  18,500. 

The  following  table  shows  the  relative  values  of  petroleum  and 
coal.  It  is  based  on  the  following  assumed  data :  B.  T.  U.  per  lb. 
of  oil  19,000;  sp.  gr.,  0.90;=  7.5  Ibs.  per  gal.;  1  barrel=42  gals. 
=  315  Ibs. 


Coal,  B.T.U.  per  lb. 

1  lb.  Coal  =lbs.  Oil. 

.  Ibbl.  Oil=  Ibs.  Coal. 

1  Ton  Coal=bbl.  Oil. 

10,000 
11,000 
12,000 
13,000 
14,000 
15,000 

1.9 

1.727 
1.583 
1.462 
1.357 
1.267 

598 
544 
499 
460 
427 
399 

3.34 

3.68 
4.01 
4.34 
4.68 
5.01 

From  this  table  we  see  that  if  coal  of  a  heating  value  of  only 
10,000  B.T.U.  per  lb.  costs  $3.34  per  ton,  and  coal  of  14,000  B.T.U. 
per  lb.  $4.68  per  ton,  then  the  price  of  oil  will  have  to  be  as  low 
as  $1  a  barrel  to  compete  with  coal;  or,  if  the  poorer  coal  is  $3.34 
and  the  better  coal  $4.68  per  ton,  then  oil  will  be  the  cheaper  fuel 
if  it  is  below  $1  per  barrel. 

Specifications  for  fuel  oil  adopted  by  the  Southern  Pacific  Rail- 
way system  (1911)  contain  the  following:  It  must  contain  no  sand 
or  foreign  matter  in  the  shape  of  sticks,  waste,  stones,  etc.,  and 
must  be  sufficiently  liquid  to  flow  readily  in  4-inch  pipes  at  a  tern- 


188  STEAM-BOILER   ECONOMY. 

perature  of  70°  F.  It  must  contain  as  little  water  as  possible,  and 
oil  containing  more  than  2  per  cent  of  water  and  other  impurities 
will  not  be  accepted. 

Fuel  oil  will  not  be  accepted  for  general  use,  the  flash  point  of 
which  is  less  than  110°  F.  when  tested  in  the  open  cup,  Tagliabue 
method.  The  oil  to  be  heated  at  rate  of  5°  per  minute,  and  test 
flame  applied  every  5°,  beginning  at  90°.  This  flash  point  being 
the  danger  point  at  which  the  oil  begins  to  give  off  inflammable 
gases,  the  fire  or  burning  point  is  not  required. 

The  specific  gravity  of  fuel  oil  should  range  between  13°  and 
29°  Baume  at  60°  F. 

Oil  vs.  Coal  as  Fuel.— A  test  by  the  Twin  City  Eapid  Transit  Com- 
pany of  Minneapolis  and  St.  Paul  showed  that  with  the  ordinary  Lima 
oil  weighing  6^  pounds  per  gallon,  and  costing  2|  cents  per  gallon, 
and  coal  that  gave  an  evaporation  of  7J  Ibs.  of  water  per  pound  of 
coal,  the  two  fuels  were  equally  economical  when  the  price  of  coal  was 
$3.85  per  ton  of  2000  Ibs.  With  the  same  coal  at  $2.00  per  ton,  the 
coal  was  37  per  cent  more  economical,  and  with  the  coal  at  $4.85  per 
ton,  the  coal  was  20  per  cent  more  expensive  than  the  oil.  These 
results  include  the  difference  in  the  cost  of  handling  the  coal, 
ashes,  and  oil.* 

In  1892  there  were  reported  to  the  Engineers'  Club'  of  Phila- 
delphia some  comparative  figures,  from  tests  undertaken  to  ascertain 
the  relative  value  of  coal,  petroleum,  and  gas. 


Lbs.  Water,  from 
and  at  212°  F. 

1  lb  anthracite  coal  evaporated                                           

9   70 

1  lb  bituminous  coal 

10  14 

1  lb  fuel  oil  36°  gravity 

16  48 

1  cubic  foot  gas  20  C  P                                           .... 

1  28 

The  gas  used  was  that  obtained  in  the  distillation  of  petroleum, 
having  about  the  same  fuel  value  as  natural  or  coal-gas  of  equal 
candle  power. 

Taking  the  efficiency  of  bituminous  coal  as  a  basis,  the  calorific 
energy  of  petroleum  is  more  than  60%  greater  than  that  of  coal; 
whereas,  theoretically,  petroleum  exceeds  coal  only  about  45% — the 
one  containing  14,500  heat-units,  and  the  other  21,000. 

*  Iron  Age,  Nov.  2,  1893. 


FUELS   OTHER   THAN  COAL.  189 

Comparative  tests  of  crude  petroleum  and  of  Indiana  block  coal 
for  steam-raising  at  the  South  Chicago  Steel  Works*  showed  that, 
with  coal,  14  tubular  boilers  16  ft.  X  5  ft.  required  25  men  to  oper- 
ate them;  with  fuel  oil,  6  men  were  required,  a  saving  of  19  men 
at  $2  per  day,  or  $38  per  day. 

For  one  week's  work  2731  barrels  of  oil  were  used,  against  848 
tons  of  coal  required  for  the  same  work,  showing  3.22  barrels  of 
oil  to  be  equivalent  to  1  ton  of  coal.  With  oil  at  60  cents  per  barrel 
and  coal  at  $2.15  per  ton,  the  relative  cost  of  oil  to  coal  is  as  $1.93 
to  $2.15.  No  evaporation  tests  were  made. 

Specifications  for  the  Purchase  of  Fuel  Oil. — The  U.  S.  Bureau 
of  Mines  has,  in  Technical  Paper  No.  3,  1911,  the  following  speci- 
fications, which  were  drawn  up  for  the  government,  covering  (1) 
the  number  of  heat-units  obtained  for  a  given  price,  (2)  the  physical 
character  of  the  oil,  (3)  flash  and  burning  points,  and  (4)  amounts 
of  extraneous  matter. 

Fuel  oil  should  be  either  a  natural  homogeneous  oil  or  a  homo- 
geneous residue  from  a  natural  oil;  if  the  latter,  all  constituents 
having  a  low  flash  point  should  have  been  removed  by  distillation; 
it  should  not  be  composed  of  a  light  oil  and  a  heavy  residue  mixed 
in  such  proportions  as  to  give  the  density  desired. 

It  should  not  have  been  distilled  at  a  temperature  high  enough 
to  burn  it,  nor  at  a  temperature  so  high  that  flecks  of  carbonaceous 
matter  began  to  separate. 

It  should  not  flash  below  60°  C.  (140°  F.)  in  a  closed  Abel- 
Pensky  or  Pensky-Martens  tester. 

Its  specific  gravity  should  range  from  0.85  to  0.96  at  15°  C. 
(59°  F.)  ;  the  oil  should  be  rejected  if  its  specific  gravity  is  above 
0.97  at  that  temperature. 

It  should  be  mobile,  free  from  solid  or  semi-solid  bodies,  and 
should  flow  readily,  at  ordinary  atmospheric  temperatures  and  under 
a  head  of  1  ft.  of  oil,  through  a  4-in.  pipe  10  ft.  in  length. 

It  should  not  congeal  nor  become  too  sluggish  to  flow  at  0°  C. 
(32°  F.). 

It  should  have  a  calorific  value  of  not  less  than  18,000  B.T.U. 
per  Ib. ;  18,450  B.T.U.  per  Ib.  to  be  the  standard.  A  bonus  is  to 
be  paid  or  a  penalty  deducted  according  to  the  method  stated  under 
section  21,  as  the  fuel  oil  delivered  is  above  or  below  this  standard. 

It  should  be  rejected  if  it  contains  more  than  2%  water. 

It  should  be  rejected  if  it  contains  more  than  1%  sulphur. 

It  should  not  contain  more  than  a  trace  of  sand,  clay,  or  dirt. 

*  Trans.  A.  I.  M.  E.,  xvii.  p.  807. 


190  STEAM-BOILER  ECONOMY. 

Viscosity  of  Oils  at  Different  Temperatures.  (E.  EL  Peabody, 
Proc.  Soc.  Naval  Archts.  &  Marine  Engrs.,  1912.) — Figures  approxi- 
mated from  plotted  curves.  Tests  by  Engler  viscosimeter. 


Temp,  of  oil, 
deg.  F  
Beaumont, 
Tex.,  oil.  .  . 
California.  .  . 

Sp.  Gr. 
0.936 
.962 
.970 

Flash  Point. 
236°  F. 
282 
260 

100 

120      140      160     180    200    220    240 

5 
23 
50 

3        2         1.2     1.0    0.8 
13       6.5     3.6    2.1     1.5     1 
29      11.5     5.       2.9     1.8     1.2     — 

.974      280  54       33      12.5     7.4     5.       3.6    2.7      2 

With  all  ordinary  oils  heating  to  within  50°  F.  of  the  flash  point 
is  sufficient  to  render  them  suitable  for  use  with  mechanical  burners. 
Many  of  the  lighter  oils  are  sufficiently  limpid  at  ordinary  tempera- 
tures to  be  used  without  heating. 

Use  of  Heavy  Oil. — Mexican  crude  oil  is  very  sticky  and  viscous 
at  80°  F.  On  heating  to  212°  it  turned  to  foam  owing  to  the  pres- 
ence of  water  which  failed  to  separate  out.  Sp.  gr.  at  60°,  0.981, 
or  12.5  Baume.  Moisture  and  silt  3.5% ;  flash  point  310° ;  burning 
point  347°  ;  B.T.TJ.  per  Ib.  17,551.  Was  successfully  sprayed  and 
burned  under  natural  draft  on  being  heated  to  270°  at  a  pressure 
of  165  Ibs.  The  capacity  fell  off  about  40%  from  that  obtained  with 
the  same  apparatus  with  oil  of  18°  Baume. 

Tar  as  Fuel.* — Under  normal  conditions  coal  tar  has  a  value  for 
other  purposes  exceeding  its  fuel  value  considerably;  but  this  is  not 
always  true,  and  it  is  seldom  that  what  is  ordinarily  called  water-gas 
tar  can  be  disposed  of  at  a  price  near  its  fuel  value. 

The  yield  of  coal  tar  produced  by  the  distillation  of  coal  varies, 
according  to  the  coal  and  the  method  employed,  from  4.5  to  6.5  per 
cent  of  the  weight  of  coal.  Its  specific  gravity  is  about  1.25,  a 
gallon  weighing  10.3  Ibs.  The  ultimate  analysis  of  a  tar  made  from 
a  standard  gas  coal,  in  a  medium-sized  gas  works,  is  as  follows : 

Carbon,  89.21;  hydrogen,  4.95;  nitrogen,  1.05;  oxygen,  4.23; 
ash,  trace;  volatile  sulphur,  0.56.  Heating  value  by  Dulong's 
formula,  15,781  B.  T.  U.  per  Ib.  A  series  of  tests  in  a  bomb  calorim- 
eter gave  15,708  British  thermal  units,  the  tar  being  practically  freed 
from  water. 

Gas-works  Residuals  as  Fuel, — The  value  of  coke,  coke  breeze, 
coal-tar  and  water-gas  tar  as  fuel  for  steam  boilers  is  discussed  by 

*  C.  F.  Pritchard,  in  The  Engineer  (Chicago),  April  1,  1903. 


FUELS  OTHER  THAN  COAL.  191 

C.  F.  Pritchard,  (Power,  May,  1902).  A  coke  made  from  a  standard 
gas  coal  analyzed  as  follows:  Moisture  1.12;  volatile  matter  3.38; 
ash  8.75;  fixed  carbon  86.75;  sulphur  0.84,  B.T.U.  per  Ib.  calculated 
13,341 ;  by  calorimeter  13,469  per  Ib. ;  coke,  14,944  per  Ib.  combustible. 
Monthly  records  of  water  evaporated  by  coke  and  by  Cumberland, 
Md.,  semi-bituminous  coal  showed  that  the  coke  was  practically  of 
the  same v  value  per  pound  as  the  coal,  the  evaporation  from  and  at 
212°  per  Ib.  of  fuel  ranging  from  8.7  to  11.1  Ibs.,  the  lower 
figure  being  obtained  both  with  coal  alone  and  with  coke  used  to 
replace  more  than  half  of  the  coal.  The  higher  figure  was  obtained 
in  a  month  when  the  relative  proportions  of  coal  and  coke  were  about 
as  4  to  3.  A  test  with  coke  alone  gave  an  evaporation  of  10.39  Ibs. 
from  and  at  212°  per  pound  of  coke.  The  best  method  of  burning 
coke  was  found  to  be  using  a  deep  furnace,  with  the  grate  bars  at 
the  ground  level  and  carrying  a  bed  of  coke  2^2  to  3  ft.  thick.  Heated 
air  for  burning  the  gas  made  from  the  coke  was  furnished  through 
a  hollow  bridge  wall.  Tests  were  made  with  one-fifth  of  coke  breeze 
added  to  the  coke,  and  also  with  coke  breeze  added  to  coal  in  various 
proportions,  and  after  deducting  the  evaporation  credited  to  the  coal 
(9.25  Ibs.)  the  evaporation  due  to  the  addition  of  breeze  was  found 
to  range  from  5.3  to  7. 1  Ibs.  from  and  at  212°  per  Ib.  of  breeze. 

Coal  tar  of  a  heating  value  of  15,708  B.T.U.  per  Ib.  was  tested 
with  results  ranging  from  11.07  to  12.22  Ibs.  from  and  at  212° 
per  Ib.  of  tar.  It  is  believed  that  much  better  results  could  be  obtained 
under  more  favorable  conditions.  Water-gas  tar  made  from  gas 
oil  was  also  tested.  Its  analysis  was  C,  92.70;  H,  6.13;  ]ST,  0.11; 
0,  0.69;  ash,  trace;  volatile  S,  0.37;  specific  gravity  1.15;  heating 
value  by  calorimeter,  17,193  B.T.U.  per  Ib.  Eleven  tests  gave  results 
ranging  from  13.08  to  16.20  Ibs.  from  and  at  212°  per  Ib.  tar, 
averaging  14.9  Ibs.  Mr.  Prichard  concludes  that  taking  steam  coal 
at  $3.75  per  ton  of  2000  Ibs.  a  fair  market  value  for  coke  would  be 
$3.75;  coke  breeze,  per  ton,  $2.48;  coal-gas  tar  and  water-gas  tar,  per 
barrel  of  50  gallons,  respectively  $1.38  and  $1.39. 

Gas  Fuel. — Natural  gas  is  an  ideal  fuel  for  steam-boilers  wherever 
it  can  be  obtained  in  sufficient  quantity  and  at  reasonable  cost  as 
compared  with  coal.  About  1890  it  was  in  quite  general  use  in 
western  Pennsylvania  and  in  many  places  in  Ohio  and  Indiana,  when 
numerous  wells  furnished  vast  quantities  of  gas  at  a  high  pressure, 
but  in  a  few  years  the  supply  diminished  and  it  became  too  high  in 
price  to  be  commonly  used  in  steam-boilers.  Its  use  is  now  confined 
chiefly  to  household  purposes.  The  following  are  some  analyses  :* 

*  Engineering  and  Mining  Journal,  April  21,  1894. 


192 


STEAM-BOILER  ECONOMY. 


NATURAL    GAS    IN    OHIO    AND    INDIANA. 


Description. 

Ohio. 

Indiana. 

Fos- 
toria. 

Find- 
lay. 

St. 
Mary's 

Muncie. 

Ander- 
son. 

Koko- 
mo. 

Marion. 

Hydrogen  
Marsh-gas  
Olefiant  gas  
Carbon  monoxide.  .  . 
Carbon  dioxide. 

1.89 
92.84 
.20 
.55 
.20 
.35 
3.82 
.15 

1.64 
93.35 
.35 
.41 
.25 
.39 
3.41 
.20 

1.94 
93.85 

.20 
.44 
.23 
.35 

2.98 
.21 

2.35 
92.67 
.25 
.45 
.25 
.35 
3.53 
.15 

1.86 

93.07 
.47 
.73 
.26 
.42 
3.02 
.15 

1.42 
94.16 
.30 
.55 
.29 
.30 
2.80 
.18 

1.20 
93.57 
.15 
.60 
.30 
.55 
3.42 
.20 

Oxygen.  . 

N  itrogen  . 

Hydrogen  sulphide 

Approximately  30,000  cubic  feet  of  gas  has  the  heating  power  of 
one  ton  of  coal. 

The  following  analyses  are  given  by  J.  M.  Whitham  in  Trans. 
A.  S.  M.  E.,  1905: 

NATURAL    GAS    IN   PENNSYLVANIA    AND    WEST   VIRGINIA 


Illuminants.                                  .    .  . 

0  45 

0.15 

0  50 

1  6 

Carbonic  oxide                                 .    .  . 

0  00 

0  00 

0  15 

1  8 

Hydrogen                                             .  . 

0  20 

0  30 

0  25 

0  3 

Marsh  gas. 

81  05 

83  20 

83  40 

81  9 

Ethane. 

17  60 

15  55 

15  40 

13  2 

Carbonic  acid. 

0  00 

0  20 

0  00 

0  0 

Oxygen 

0  15 

0  10 

0  00 

0  4 

Nitrogen 

0  55 

0  50 

0  30 

0  8 

B.T.U.  per  cu.  ft.  at  60°  F.  and  14.7 
barometer 

1030 

1020 

1026 

1098 

The  first  three  analyses  are  of  gas  from  nine  wells  in  Lewis  Co.,  W.  Va., 
the  last  is  from  a  mixture  from^  fields  in  three  States  supplying  Pittsburgh,  Pa. 

Producer-gas. — Since  the  invention  of  the  Siemens  producer  and 
regenerative  furnace,  in  1856,  and  their  general  introduction  into 
metallurgical  and  glass  works,  many  attempts  have  been  made  to  use 
producer-gas  as  a  fuel  for  steam-boilers,  the  evident  advantage  being 
the  ease  of  conveying  the  gas  in  pipes  from  a  centrally-located  pro- 
ducer-plant to  a  number  of  boilers,  the  facility  of  operation  of  the 
boilers  with  gaseous  fuel,  and  the  saving  of  labor.  These  attempts 
have  generally  failed,  however,  on  account  of  the  facts  that  the  gas- 
making  process  always  entailed  some  loss  of  heat,  that  the  producers 
were  of  too  great  cost,  and  that  it  was  difficult  to  drive  them  at  the 
varying  rates  usually  required  in  steam-boiler  practice.  The  follow- 
ing analysis  of  producer-gas  is  given  by  W.  H.  Blauvelt:* 

*  Trans.  A.  I.  M.  E.,  xviii.  p.  614. 


FUELS  OTHER  THAN  COAL. 


193 


PRODUCER-GAS  FROM  ONE  TON  OF  COAL. 


Analysis  by 
Volume. 

Per  Cent. 

Cubic  Feet. 

Pounds. 

Equal  to 

CO 

25  3 

33,213.84 

2451.20 

1050.51  Ibs.  C  +  1400.7  Ibs.  O. 

H           

9.2 

12,077.76 

63.56 

63  .  56         H. 

CH4   

3.1 

4,069.68 

174.66 

174.66        CH4. 

C2H4  
CO  
N  (by  difference, 

0.8 
3.4 

58.2 

1,050.24 
4,463.52 
76,404.96 

77.78 
519.02 
5659.63 

77.78         C2H4. 
141.54        C  +377.44  Ibs.  O. 
7350.17         Air. 

100.0 

131,280.00 

8945.85 

Calculated  upon  this  basis,  the  131,280  ft.  of  gas  from  the  ton  of 
coal  contained  20,311,162  B.T.U.,  or  155  B.T.U.  per  cubic  foot,  or 
2270  B.T.U.  per  Ib. 

The  composition  of  the  coal  from  which  this  gas  was  made  was 
as  fonows:  Water,  1.26%;  volatile  matter,  36.22%;  fixed  carbon, 
57,98%;  sulphur,  0.70%;  ash,  3.78%.  One  ton  contains  1159.6  Ibs. 
carbon  and  724.4  Ibs.  volatile  combustible,  the  energy  of  which  is 
31,302,200  B.T.U.  Hence,  in  the  processes  of  gasification  and  puri- 
fication there  was  a  loss  of  35.2%  of  the  energy  of  the  coal. 

The  following  table  of  comparative  analyses  and  heating  values 
of  different  kinds  of  gas  is  given  by  W.  J.  Taylor:* 


Natural 
Gas. 

Coal- 
gas. 

Water- 
gas. 

Producer-gas. 

Anthra. 

Bitumin. 

CO.  . 

0.50 
2.18 
92.6 
0.31 
0.26 
3.61 
0.34 

6.0 
46.0 
40.0 
4.0 
0.5 
1.5 
0.5 
1.5 
32.0 
735,000 

45.0 
45.0 
2.0 

i'6 
2.0 
0.5 
1.5 
45.6 
322,000 

27.0 
12.0 
1.2 

'2.5 
57.0 
0.3 

65^6 
137,455 

27.0 
12.0 
2.5 
0.4 
2.5 
56.2 
0.3 

65*9 
156,917 

H  

CH4 

C2H4 

CO2    . 

N     

O  

Vapor  

Pounds  in  1000  cubic  feet  .  .  . 
Heat-units  in  1000  cubic  feet  . 

45.6 
1,100,000 

Corn  as  Fuel. — It  was  once  common  in  Nebraska,  in  years  when  the 
corn  crop  was  abundant  and  selling  prices  low,  to  use  corn  instead  of 
coal  as  fuel.  Prof.  C.  R.  Richards  reports  in  Cassier's  Magazine  the 
results  of  two  boiler  tests,  one  with  corn  and  one  with  good  Rock 


*  Trans.  A.  I.  M.  E.,  xviii.  p.  205. 


194 


STEAM-BOILER  ECONOMY. 


Springs  bituminous  coal,  costing  in  Lincoln,  Neb.,  $6.65  per  ton. 
The  results  showed  that  the  coal  gave  1.9  times  as  much  heat  per  Ib. 
as  the  corn.  Tests  of  both  fuels  in  a  fuel  calorimeter  gave  7076 
B.T.U..  for  the  corn,  and  13,010  for  the  coal,  a  ratio  of  1  to  1.86. 
Other  calorimeter  tests  of  different  sample  of  corn  gave  results  as 
follows : 

THE  HEATING  VALUE  OF  CORN. 


Kind  of  Material. 

Heating  Value  in  B.T.U. 

Per  Ib.  of 
Material. 

Per  Ib.  of  Dry 
Material. 

Per  Ib.  of  Dry 
Combustible. 

Yellow  Dent  corn  n,n<l  cob 

8040 
8202 
7214 
7841 
8382 
7571 

8959 

7841 

9199 
8174 

9085 
7958 

930i 

8285 

Yellow  Dent  corn  
Yellow  Dent  cob         .        

White  Dent  corn  and  cob  

White  Dent  corn        •. 

White  Dent  cob.    .        

Assuming  the  average  heating  value  of  Nebraska  coal  at  11,500 
B.T.U.  per  Ib.,  that  of  corn  8040  B.T.U.,  and  the  weight  of  corn  56 
Ibs.  per  bushel,  corn  at  10  cents  per  bushel  would  be  as  cheap  a  fuel 
as  coal  at  $5.11  per  ton  of  2000  Ibs. 


CHAPTEE  VII. 

FURNACES.— METHODS  OF  FIRING.— SMOKE-PREVENTION.— 
MECHANICAL  STOKERS.— FORCED  DRAFT. 

Location  of  the  Furnace. — The  furnace,  or  fire-box,  of  a  steam- 
boiler  should  be  considered  as  an  apparatus  separate  and  distinct  from 
the  boiler  itself.  The  function  of  the  furnace  is  to  generate  heat  by 
the  combustion  of  the  fuel;  that  of  the  boiler  is  to  transfer  the  heat 
into  the  water.  The  combustion-chamber,  when  there  is  one,  is  an 
extension  of  the  fire-box;  its  office  is  to  afford  space  in  which  to 
complete  the  combustion  of  the  volatile  gases  which  are  imperfectly 
burned  in  the  fire-box. 

In  internally  fired  boilers,  such  as  the  locomotive,  marine,  Lanca- 
shire, and  vertical  tubular  boilers,  the  fire-box  is  located  inside  of  the 
boiler.  The  chief  advantage  of  this  method  of  construction  is  its 
economizing  of  space,  but  it  is  attended  with  the  disadvantages  of 
limiting  the  area  of  grate-surface,  and  thereby  limiting  the  coal-burn- 
ing capacity  of  the  boiler,  and,  with  soft  coal,  of  providing  insuf- 
ficient space  for  a  combustion-chamber,  in  which  to  burn  the  volatile 
gases.  Another  objection  to  the  internal  furnace  is  usually  that  the 
walls  of  the  fire-box  and  combustion-chamber  are  metallic  surfaces, 
kept  comparatively  cool  by  the  water  in  the  boiler,  which  chill  the 
gases  and  tend  to  prevent  their  combustion.  In  some  such  furnaces, 
however,  fire-brick  arches  or  walls  are  used,  which  have  the  beneficial 
effect  of  keeping  the  furnace  at  a  high  tmperature. 

With  other  types  of  boilers,  such  as  the  horizontal  tubular  and 
the  common  form  of  water-tube  boiler,  with  inclined  tubes,  it  is  cus- 
tomary to  locate  the  furnace  immediately  underneath  the  boiler,  be- 
tween the  brick  walls  of  the  setting.  For  horizontal  tubular  boilers 
this  method  of  setting  is  usually  satisfactory,  for  the  width  between 
the  side-walls  of  the  setting  is  sufficient  to  accommodate  an  ample 
area  of  grate-surface,  on  which  may  be  burned,  at  moderate  rates  of 
combustion,  all  the  coal  that  should  be  burned  for  the  amount  of  heat- 
ing surface  of  the  boiler.  When  soft  coal  is  used  this  setting  allows 

195 


196  STEAM-BOILER  ECONOMY 

of  a  long  travel  of  the  gases,  which  is  favorable  to  their  combustion, 
and  furthermore,  it  furnishes  sufficient  space  in  which  to  build  fire- 
brick arches,  baffle-walls,  or  other  devices  to  more  perfectly  secure 
complete  combustion. 

With  water-tube  boilers  of  the  inclined-tube  form,  this  location  is 
unobjectionable  when  large  sizes  of  anthracite  coal  are  used ;  in  this 
case  the  grate-surface  is  sufficiently  large  to  burn  with  moderate  draft 
all  the  coal  that  is  required  to  develop  the  full  economical  capacity  of 
the  boiler,  and  the  small  quantity  of  volatile  gases  is  easily  burned  in 
the  fire-box.  With  small  sizes  of  coal  this  setting  does  not  provide 
sufficient  space  for  grate-surface  enough  to  develop  the  usual  rated 
capacity  of  the  boiler,  unless  a  very  strong  draft  is  provided  either  by 
a  tall  chimney  or  by  mechanical  means.  The  fine  sizes  of  anthracite 
usually  contain  a  considerable  percentage  of  moisture,  which  forms 
combustible  gas  by  its  decomposition  by  red-hot  carbon,  some  of  which 
gas  is  apt  to  escape  unburned  unless  abundant  room  is  provided  for 
burning  it  in  the  fire-box. 

For  bituminous  coal  the  ordinary  setting  of  an  inclined  water-tube 
boiler,  with  the  air-passages  rising  immediately  above  the  furnace  into 
the  nest  of  tubes  above,  is  .entirely  unsuitable.  There  is  insufficient 
room  in  the  furnace  for  the  burning  of  the  gases;  they  are  chilled  by 
the  water-tubes  above  the  furnace;  they  deposit  soot  upon  them, 
diminishing  the  effectiveness  of  the  heating  surface,  and  a  large  pro- 
portion of  the  gas  escapes  unburned.  A  furnace  which  provides  a 
long  travel  of  the  gases  under  a  fire-brick  roof,  before  they  are  allowed 
to  enter  the  nest  of  tubes,  such  as  the  setting  of  the  Heine  boiler,  is 
an  improvement  in  this  respect,  but  such  a  furnace  is  not  well 
adapted  to  boilers  having  more  than  seven  horizontal  rows  of  tubes, 
unless  transverse  baffle  walls  are  built  in  the  air  passage  along  the 
tubes  (or  a  longitudinal  baffle  made  of  tiles  carried  on  one  of  the  hori- 
zontal rows  of  tubes  near  the  middle  of  the  bank),  otherwise  the  pas- 
sage is  of  too  large  an  area  in  cross-section  to  cause  the  current  of  hot 
gas  to  completely  envelop  all  the  tubes,  and  it  therefore  allows  of 
"short-circuiting,"  rendering  some  of  the  heating  surface  ineffective. 

External  fire-brick  furnaces,  commonly  called  "Dutch  ovens,"  are 
used  with  the  vertical  types  of  water-tube  boilers,  and  to  some  extent 
with  the  inclined-tube  boilers,  with  great  advantage.  When  properly 
designed  they  admit  of  sufficient  areas  of  grate-surface,  and  of  the 
use  of  deflecting  arches,  baffle-walls,  etc.,  for  insuring  combustion  of 
the  gases. 


FURNACES.— METHODS  OF  FIRING,  ETC.  197 

Requirements  of  a  Good  Furnace. —  (1)  It  should  have  ample 
coal-burning  capacity.  It  should  be  able  to  burn  the  amount  of  coal 
needed  to  generate  the  maximum  quantity  of  steam  that  may  be 
required  during  any  hour  of  the  day,  under  the  most  unfavorable 
conditions  that  may  be  expected,  such  as  atmospheric  or  other  con- 
ditions tending  to  diminish  the  chimney  draft,  and  coal  of  a  poorer 
quality  than  is  usually  furnished. 

(2)  The  grates  should  be  of  such  a  kind  that  ash  and  clinker  may 
be  easily  removed  from  them  without  stopping  the  operation  of  the 
boiler  for  more  than  a  few  minutes  at  a  time,  and  the  bars  should  be 
so  spaced  that  coal  is  not  apt  to  be  wasted  by  falling  through  them, 

(3)  It  should  be  so  constructed  as  to  be  capable  of  burning  thor- 
oughly all  the  gases  that  may  be  distilled  from  the  fuel  before  they 
come  in  contact  with  the  comparatively  cool  heating  surfaces  of  the 
boiler.     This  means  a  large  combustion  chamber  and  provision  for 
mixing  the  combustible  gases  with  the  air  supply. 

(4)  It  should  be  durable,  free  from  breakdowns  of  coal-feeding 
appliances  or  shaking  grates,  and  from  melting  down  of  fire-brick 
arches. 

(5)  Furnaces  of  externally  fired  boilers  should  be  built  with  thick 
walls,  so  as  to  minimize  as  far  as  possible  loss  of  heat  by  radiation,  or 
preferably  with  double  walls  with  air-spaces  between.     The  air-spaces 
may  with  advantage  be  so  arranged  as  to  cause  a  current  of  air  to 
flow  through  them  into  the  ash-pit  or  above  the  fire. 

Burning  of  Anthracite  Coal. — For  large  sizes  of  anthracite,  such 
as  egg,  almost  any  kind  of  furnace  is  suitable,  and  no  great  degree  of 
skill  is  needed  to  fire  the  coal  so  as  to  obtain  the  best  results.  With  all 
ordinary  proportions  of  grate  and  heating  surface  a  moderate  draft 
suffices  to  burn  enough  coal  to  drive  the  boiler  up  to  and  beyond  its 
economical  rating.  Hand-firing  is  generally  used  with  this  coal,  and 
all  that  the  fireman  needs  to  do  is  to  keep  the  bed  of  coal  level  and 
of  a  depth  proportionate  to  the  force  of  the  draft,  to  watch  carefully 
to  prevent  the  formation  of  air-holes  in  the  bed  of  coal,  and  to  clean 
the  fire  at  long  intervals  of  time,  say  from  six  to  ten  hours.  When 
there  is  plenty  of  draft  the  fireman  has  control  of  two  factors  govern- 
ing the  combustion,  viz.,  the, damper  and  the  thickness  of  the  bed  of 
coal,  which  he  can  regulate  at  his  pleasure.  With  a  given  force  of 
draft,  which  may  be  controlled  by  the  damper,  if  the  bed  of  coal  is 
too  thin  an  excessive  supply  of  air  passes  through  it,  causing  a  waste 
of  heat  in  the  chimney  gases;  if  it  is  too  thick  some  of  the  carbon 


198  STEAM-BOILER  ECONOMY. 

•will  be  burned  only  to  carbon  monoxide,  instead  of  to  carbon  dioxide, 
causing  a  great  loss  of  heat.  The  latter  source  of  loss,  when  there  is 
sufficient  draft  available,  may  easily  be  prevented,  for  it  makes  itself 
known  by  a  sluggish  action  of  the  fire,  the  presence  of  blue  flames  on 
the  bed  of  coal,  and  low  temperature  of  the  furnace.  The  remedy  is 
either  to  carry  a  thinner  bed  of  fire,  or  to  open  the  damper  and  give 
a  stronger  draft  in  the  furnace.  The  loss  due  to  excess  of  air  on 
account  of  too  thin  a  bed  of  coal  is  much  more  common,  and  its  effect 
in  the  furnace  is  not  so  apparent  to  the  fireman.  It  may  be  prevented 
by  carrying  as  thick  a  bed  of  coal  as  will  not  cause  the  temperature 
of  the  furnace  to  be  visibly  lowered  and  blue  flames  to  make  their 
appearance. 

In  all  cases  the  highest  possible  temperature  of  the  furnace  gives 
the  highest  economy,  provided  the  heating  surface  is  of  sufficient 
extent  to  absorb  the  proper  proportion  of  the  heat  generated,  and  to 
cool  the  gases  to  the  lowest  practicable  temperature  before  they  reach 
the  chimney-flue.  The  highest  temperature  is  obtained  by  firing  small 
quantities  of  coal  at  a  time  and  by  keeping  the  bed  of  coal  at  such  a 
thickness  as  will  insure  complete  combustion  without  an  excessive 
supply  of  air  passing  through  it. 

With  small  sizes  of  anthracite  there  is  more  difficulty  in  securing 
the  best  conditions  of  combustion.  The  fineness  of  the  coal  tends  to 
choke  the  air-passages  through  the  bed  on  the  grate,  and  a  thinner 
bed  has  therefore  to  be  carried  unless  there  is  a  very  strong  draft,,  and 
a  thin  bed  is  more  difficult  than  a  thick  one  to  keep  free  of  air-holes. 
The  coal  is  usually  much  higher  in  ash  than  large-sized  coal,  and  the 
fires  therefore  need  to  be  cleaned  oftener — an  operation  which  always 
chills  the  fire,  decreasing  the  rate  of  steaming,  and  causes  a  waste  of 
heat.  The  evaporation  per  pound  of  combustible  with  fine  sizes  of 
coal  is  usually  in  ordinary  practice  considerably  less  than  with  egg 
coal. 

In  order  to  burn  a  sufficient  quantity  of  fine  sizes  of  anthracite 
coal  to  develop  the  required  capacity  of  a  boiler  it  is  common  to  use 
a  forced  blast  provided  either  by  a  fan  or  by  a  steam- jet. 

Burning  Small  Sizes  of  Anthracite. — The  report  of  the  Penn- 
sylvania State  Commission  on  "Waste  of  Coal  Mining,"  1883,  con- 
tains the  following: 

A  number  of  experiments  were  made  in  the  testing  laboratory  of 
Coxe  Bros.  &  Co.,  by  Mr.  John  R.  Wagner,  in  burning  small  coals 


FURNACES.— METHODS  OF  FIRING,  ETC.  199 

with  a  forced  draft,  obtained  in  one  case  by  a  fan  and  in  the  other 
by  a  steam-jet.    They  showed : 

"First. — That  the  ashes  produced  by  a  steam-jet  were  never  as 
low  in  carbon  as  those  produced  by  the  fan;  that  is,  an  appreciably 
larger  per  cent  of  the  carbon  was  utilized  by  the  fan-blast.  This 
appears  to  be  due  to  the  fact  that  when  the  carbon  in  the  ash  over 
the  grate  is  reduced  to  a  certain  point  the  steam  dampens  it  some- 
what, and  it  ceases  to  burn  sooner  than  it  does  when  dry  air  only  is 
blown  through  it. 

"  Second. — That  with  the  .fan-blast  the  rate  of  combustion  per 
square  foot  per  hour  is  greater  than  with  the  steam-jet. 

"Third. — It  was  found  that  where  a  bed  of  coal  was  ignited  and 
burned  out,  the  percentage  of  carbon  in  the  ash  is  much  less  than 
where  coal  is  successively  added  to  the  burning  mass.  In  practice 
it  is  not  generally  possible  to  allow  the  bed  to  burn  out  sufficiently 
before  adding  the  cold,  unignited  coal;  the  result  is  a  damping 
down  of  the  fire,  which  causes  the  ash  to  cease  burning  sooner  than 
it  would  do  if  there  were  no  reduction  of  temperature  and  checking 
of  the  draft  due  to  the  adding  of  the  coal. 

"Fourth. — There  seems  to  be  no  doubt  that  the  introduction  of 
steam  into  the  ash-pit  decreases  very  materially  the  tendency  of  the 
coal  to  clinker  on  the  grate  in  comparison  with  the  fan-blast  or  nat- 
ural draft.  It  also  changes  the  color,  volume,  and  character  of  the 
flame,  and,  owing  to  producer  action,  increases  the  distance  that  the 
flame  extends  beyond  the  bridge-wall.  In  many  cases  it  is  not  prac- 
ticable or  at  least  it  is  very  difficult,  to  fire  the  smaller  sizes  of  coal 
without  the  steam-jet  on  account  of  the  clinkering.  This  effect  of 
steam  on  clinkering  is  probably  due  to  the  fact  that  the  steam,  to  a 
certain  extent,  moistens  the  ash  close  to  the  grate  and  prevents  the 
ash  from  reaching  there  at  as  high  a  temperature  as  it  would  with  dry 
air.  It  is  also  probable  that  the  decomposition  of  the  steam  into  car- 
bonic oxide  and  hydrogen,  which  takes  place  to  a  certain  extent,  and 
which,  of  course,  is  accompanied  by  a  reduction  of  temperature,  tends 
to  prevent  clinkering.  The  decomposition  of  the  steam,  accompanied 
by  the  formation  of  carbonic  oxide  and  hydrogen,  will  probably  ac- 
count for  the  difference  in  the  flame  referred  to. 

"Fifth. — A  careful  study  of  the  burning  of  culm,  that  is,  the 
burning  of  small  coals  with  more  or  less  dust  in  them,  in  these  and 
other  experiments,  seemed  to  show  that  in  almost  all  cases  it  is 
accompanied  by  a  very  high  percentage  of  carbon  in  the  ash,  which 
analysis  showed,  in  some  cases,  reached  58  per  cent.  Unless  special 
precautions  are  taken  to  prevent  it,  a  large  portion  of  the  fine  coal 
runs  down  through  the  grate.  When  the  culm  gets  red  hot  it  acts 
almost  like  dry  sand  and  works  its  way  into  the  ash-pit,  thus  increas- 
ing largely  the  percentage  of  carbon.  Where  coal  has  to  be  trans- 
ported any  distance,  the  value  of  the  culm  at  the  mines  being  very 


200  STEAM-BOILER  ECONOMY. 

small,  it  is  probable  from  the  investigations  made,  that  it  would  be 
cheaper  to  remove  the  dust  and  transport  only  the  larger  coal.* 

"  Sixth. — It  has  been  found  that  the  percentage  of  iron  pyrites, 
which  occurs  to  a  greater  or  less  extent  in  all  coals,  increases  very 
rapidly  with  the  smallness  of  the  coal.  This  is  due  to  the  fact  that 
the  iron  pyrites  occur  generally  in  thin  layers  or  in  incrustations  on 
the  coal.  These  thin  layers  are  broken  off  and  pulverized  in  the 
preparation  and  handling  of  the  coal,  and  are  therefore  found  to  a 
much  greater  extent  in  the  very  small  coal.  It  is,  of  course,  well 
known  that  the  presence  of  iron  pyrites  in  fuel  is  very  undesirable,  as 
it  generates  sulphurous  acid  and  has  a  tendency  to  destroy  the  grates 
or  other  iron-work  around  the  boilers,  besides,  in  many  cases,  increas- 
ing the  tendency  to  clinker. 

"  Seventh. — That  while  the  fan-blast  produces  the  best  ash  and 
gives  a  more  perfect  and  greater  rate  of  combustion,  yet  in  many 
cases  it  is  more  advantageous  to  use  the  steam-blower  on  account  of 
the  clinkering,  which  may  cause  very  serious  trouble.  In  certain 
localities,  particularly  in  cities,  the  noise  of  the  steam-blower  is  some- 
times a  disadvantage. 

"Eighth. — While  it  is  not  positively  demonstrated,  it  is  thought 
that  the  question  of  mixing  small  coals  from  different  veins  of  differ- 
ent localities  is  a  matter  of  importance.  It  would  appear  that  some- 
times two  coals,  each  of  which,  when  burned  separately,  give  reason- 
ably satisfactory  results,  when  mixed  together,  clinker  and  give 
trouble,  probably  because  the  ash  of  the  combined  coals  forms  a  much 
more  fusible  silicate  than  either  of  the  ashes  separately. 

"  Ninth. — It  would  seem  that  the  combustion  of  the  small  anthra- 
cite is  more  perfect  when  the  coal  remains  undisturbed,  or  as  nearly 
as  possible  in  the  condition  in  which  it  was  put  in  the  fire,  instead 
of  being  turned  over  so  that  the  partially  consumed  and  the  uncon- 
sumed  coal  are  mixed  together." 

Comparative  Efficiency  of  Steam-  and  Fan-blowers. — The  follow- 
ing record  of  comparative  tests  of  steam-  and  fan-blowers,  made  on 
three  plain  cylinder  boilers  at  the  Short  Mountain  Colliery,  Lykens, 
Pa.,  was  published  in  the  Colliery  Engineer,  August,  1897.  The  con- 
ditions in  each  case  were  the  same,  rice  coal  being  used  as  fuel  on  a 
sectional  grate  with  12  per  cent  air-openings. 

The  fan-blower  consisted  of  a  gangway-fan  33  in.  diam.,  4  paddles 
9  ^  91  in>^  driven  by  a  small  slide-valve  engine  with  cylinder  412g-  in 

*  This  is  now  common  practice.  The  old  culm  beds  at  the  anthracite 
mines,  which  were  formerly  valueless,  are  rapidly  being  removed,  their  contents 
being  passed  through  washing  apparatus  to. remove  the  dirt  and  fine  coal,  and 
the  remainder  sorted  into  sizes  by  means  of  screens. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


201 


Dimensions  of  boilers  36  in.  diam.,  42  ft.  long. 
Area  grate-surface,  3  boilers.  .  ..61.5  sq.  ft. 

With  Steam- 
blower. 

With  Fan- 
blower. 

COAL. 

7  700  Ib 

6  100  Ib 

1  330  " 

1  027  '  ' 

6  370  " 

5  073  '  ' 

17  2  per  cent 

16  8  per  cent 

962  5  Ib 

762  5  Ib 

796  3  " 

634  1   '  ' 

WATER. 
Total  water  evaporated   actual  conditions    . 

39  241  Ib 

34  890  Ib 

Equivalent  water  evaporated  per  hour  from  and  at  212°.  .  .  . 
Water  evaporated  per  hour  per  Ib.  of  coal,  actual  conditions  . 
'     coal  from  and  at  212°  . 
"                               '  '       '  '       '  '         "     combustible  from  and 
at  212°  
H  P   developed                 

5,444  " 
5.10  " 
5.66  " 

6.84  " 
157  81  " 

4,867  " 
5.59  " 
6.38  " 

7.67  " 
141  1      " 

77  " 

78  " 

Average  temperature  of  feed-water  ... 

134° 

137° 

BLOWERS. 
Boiler  H.P.  used  by  blowers  per  hour  from  and  at  212°  
Per  cent  of  the  developed  H.P.  of  the  three  boilers  used  for 
blowers                           .         

11.9  H.P. 

5.64  H.P. 
4  per  cent 

Cubic  feet  of  air  per  minute  

2,502  ft 

3,506  ft. 

Average  water-gauge     

0  44  in 

0  52  in. 

0  173  H  P 

0  28  H  P 

REMARKS. — In  the  test  with  the  fan-blower,  the  exhaust  from  the  fan-engine  was  turned 
into  the  air-current  and  found  sufficient  to  keep  the  grates  free  from  clinker. 

Average  steam-pressure  at  steam-blowers.  ...  74  Ib. 

I. H.P.  of  fan-engine 1 . 62  H.P. 

No.  of  revolutions  of  fan-engine 160  revs. 

fan 915    " 

Useful  effect  of  fan 17% 

diam.,  7|  in.  stroke.  Steam  was  supplied  by  a  small  upright  boiler 
on  which  an  evaporative  test  was  run  during  the  test  on  the  cylinder 
boilers. 

The  steam  blower  was  made  of  j-in.  pipe,  circle  6|-  in.  diam.,  16 
holes,  tapered  -J  in.  outside,  3^-  in.  inside,  diam.  Steam  was  supplied 
by  the  upright  boiler  on  which  a  test  was  run  as  above.  Duration  of 
each  test,  8  hours. 

The  saving  of  fuel  by  the  use  of  the  fan-blower,  as  compared  with 
the  steam-blower,  was  13.9  per  cent,  taking  into  account  the  steam 
used  by  each  blower. 

Grate-bars. — Two  styles  of  grate-bars  in  common  use  are  shown 
in  Figs.  11  and  12.  The  first  is  a  plain  cast-iron  bar,  tapered  in 
cross-section,  so  as  to  make  a  wider  opening  between  the  bars  at  the 
lower  than  at  the  upper  edge.  Projections  are  cast  on  the  sides  of 
the  bars  to  keep  them  at  the  proper  distance  apart.  The  second  is 
channel-shaped  in  cross-section,  with  the  upper  surface  provided  with 
V-shaped  openings.  The  total  area  of  the  air-spaces  is  usually  made 
from  30  to  50  per  cent  of  the  total  area  of  the  grate-surface.  The 


202 


STEAM-BOILER  ECONOMY. 


width  of  the  air-spaces  and  of  the  bars  or  ribs  differs  according  to 
the  size  and  kind  of  coal  used.  For  fine  sizes  of  anthracite  the 
spaces  are  made  as  narrow  as  f  inch.  For  large  sizes  of  anthracite 


FIG.  11. — PLAIN  GRATE  BARS. 

and  for  "run-of-mine"  soft  coal  they  are  often  made  as  wide  as  1  inch. 
When  the  ash  of  the  coal  tends  to  form  clinkers,  narrow  air-spaces 
are  objectionable,  as  they  are  apt  to  become  clogged,  and  are  difficult 


TOP  AND  SIDE  VIEW. 


END  VIEW. 


FIG.  12. — "HERRING-BONE"  GRATE  BAR. 

to  keep  open  so  as  to  allow  a  sufficient  supply  of  air  to  pass  through 
them. 

The  resistance  to  the  passage  of  air  through  the  grate  and  the  bed 
of  coal  lying  upon  it  depends  upon  other  things  besides  the  size  of 
the  air-spaces  in  the  grate,  such  as  the  size  of  the  coal,  its  quality  as 
regards  coking  or  non-coking,  the  thickness  of  the  bed  of  coal  and 
ashes,  the  presence  or  absence  of  clinker,  etc.  With  coals  that  are 
low  in  ash,  and  the  ash  non-clinker  ing,  it  is  possible  to  burn  the  coal 
with  very  narrow  air-spaces  through  the  grates. 

Fine  sizes  of  anthracite  are  sometimes  burned  on  flat  cast-iron 
plates  perforated  with  tapering  holes  about  £  inch  diameter  at  the 
upper  surface,  the  total  air-space  being  about  25  per  cent  of  the 
grate-area. 

Mr.  F.  A.  Scheffler*  reports  a  test  in  which  grate-bars  of  the 
form  shown  in  Fig.  12  were  used,  with  the  air-spaces  only  about  -J  inch 
wide,  and  the  total  area  of  air-space  only  about  15  per  cent  of  the 
grate-surface.  The  coal  was  Pittsburg  run-of-mine.  With  a  draft 

.*  Trans.  A.  S.  M.  E.,  vol.  xv.  p.  503. 


FURNACES.— METHODS  OF  FIRING,  ETC.  203 

pressure  of  0.46  in  water  column,  the  rate  of  combustion  was  24.8  Ibs. 
of  coal  per  sq.  ft.  of  grate  per  hour,  a  rate  sufficient  to  drive  the 
boiler  to  much  above  its  rated  capacity. 

On  the  other  hand,  the  author  once  made  a  test  with  Illinois  coal 
containing  a  large  percentage  of  sulphur,  with  bars  of  the  same  type, 
the  air-spaces  being  |-  inch  in  width  and  with  a  draft  of  0.4  to  0.5 
inch,  but  was  unable  to  maintain,  even  with  the  maximum  draft,  a 
rate  of  combustion  sufficient  to  develop  the  rated  capacity  of  the 
boiler.  In  this  case  the  ash  fused  into  a  glass,  which  ran  into  and 
choked  the  air-spaces. 

Shaking-  and  Dumping-grates. — With  coals  of  the  character  just 
described,  shaking-  or  dumping-grates  are  almost  a  necessity,  unless 
mechanical  stokers  are  used  in  preference.  Many  different  forms  of 
such  grates  are  in  the  market.  They  may  be  divided  into  three 
general  classes:  (1)  Shaking-  or  Eocking-grates ;  (2)  Dumping- 
grates;  (3)  Shaking-  and  Dumping-grates.  In  the  first  class  the 
bars  are  usually  divided  into  small  sections,  which,  by  means  of  rock- 
ing-bars  and  levers,  are  given  an  oscillatory  or  reciprocating  motion, 
which  causes  the  ash  to  fall  through  between  the  sections.  In  the 
second  class  the  sections  are  made  larger,  and  when  the  fires  are  to  be 
cleaned  from  clinker  the  sections,  or  a  part  of  them,  such  as  those 
covering  one-quarter  of  the  whole  grate-area,  are  rocked  from  a  hori- 
zontal into  a  vertical  position,  thus  breaking  up  the  clinker  and 
allowing  it  to  fall  through  the  large  openings  thus  made.  In  the 
third  class  the  sections  are  provided  with  mechanism  by  which  either 
the  shaking  or  the  dumping  motion  may  be  given  at  will.  For  non- 
clinkering  coals  the  first  and  third  classes  are  used,  and  for  clinkering 
coals  the  second  and  third. 

The  use  of  shaking-grates  usually  entails  a  loss  of  some  unburned 
coal  through  the  grates,  amounting,  with  the  most  careful  handling, 
to  from  1  to  3  per  cent  of  the  total  coal  used;  but  this  loss  is  often 
more  than  offset  by  the  gain  due  to  the  more  complete  combustion 
which  is  obtained  when  the  air-supply  is  unrestricted  by  ash  and 
clinker. 

Furnace  for  Burning  Mb.  3  Buckwheat  Coal. — Fig.  13  shows  a 
longitudinal  section  of  a  furnace  used  with  .Babcock  &  Wilcox  boilers 
in  the  power  station  of  the  Hudson  &  Manhattan  E.  E.,  Jersey  City, 
N".  J.  (Power,  Jan.  17,  1911).  The  peculiar  features  of  this  furnace 
are  the  unusual  length  of  grate  surface,  10  ft.  from  dead  plate  to 
bridgewall,  and  the  three  fire-brick  arches  in  the  combustion  chamber. 


204 


STEAM-BOILER  ECONOMY. 


Fine  sizes  of  anthracite  are  apt  to  contain  a  great  deal  of  moisture, 
which  decomposes  when  fired  on  a  white  hot  bed  of  coal,  making 
water-gas,  and  in  order  to  burn  this  gas  before  it  becomes  chilled  by 
contact  with  the  boiler  tubes  it  is  of  advantage  to  provide  a  hot 
fire-brick  surface  for  it  to  impinge  against;  hence  these  arches.  The 
ash  and  refuse  in  this  coal  runs  from  20  to  30  per  cent,  and  it  is 
therefore  necessary  to  have  shaking  and  dumping  grates.  The 
method  of  handling  the  fire  is  thus  described:  Each  furnace  is 
9  ft.  6  in.  wide,  with  three  sections  of  grates  and  three  fire  doors. 


FIG.  13. — FURNACE  FOR  BURNING  BUCKWHEAT  COAL. 

When  the  fire  is  to  be  cleaned,  the  unconsumed  fuel  is  pushed 
back  onto  the  back  half  of  the  grate  and  the  front  half  is  dumped,  after 
which  the  live  coal  is  pulled  forward  onto  the  clean  part  and  the  rear 
section  dumped.  All  of  the  unconsumed  fuel  is  then  distributed 
over  the  entire  grate  and  fresh  fuel  added,  all  of  which  may  be  ac- 
complished in  less  than  two  minutes.  This  is  done  separately  for  each 
furnace.  Starting  thus  with  perhaps  2  ins.  of  live  coal,  the  fires 
are  allowed  to  build  up  until  in  the  course  of  6  to  7  hours  they  will 
have  attained  a  thickness  of  some  12  or  14  ins.,  two-thirds  of  which 
will  be  ash  and  only  the  top  part  live  coal.  The  cleaning  is  done  be- 
tween the  peaks  of  the  load.  The  air  pressure  used  is  from  J  to  f 


FURNACES.— METHODS  OF  FIRING,  ETC. 


205 


in.  of  water  in  the  ashpit  with  a  light  load,  and  with  J  in.  suction  in 
the  furnace.  After  the  fire  gets  to  be  4  or  5  ins.  thick  it  is  blown  with 
about  2  ins.  of  pressure  in  the  ashpit,  which  gives  a  balanced  con- 
dition in  the  furnace.  When  the  fire  is  at  its  thickest  a  blast  of  2J 
ins.  is  used.  The  average  rate  of  combustion  is  25  Ibs.  per  sq.  ft.  of 
grate  and  the  maximum  36  Ibs. 

A  24-hour  test,  divided  into  three  watches  of  8  hours  each,  gave 
the  following  results : 


l 

2 

3 

Aver- 
age. 

Evap.  from  and  at  212°  per  sq.  ft.  h.  s.  per  hr.        Lbs. 
Evap.  from  and  at  212°  per  Ib.  combustible 
Efficiency,  based  on  14,900  B.T.U.  per  Ib. 
combustible  Per  cent 

4.46 
9.91 

64.6 

4.17 
11.55 

75  2 

3.16 
11.06 

72  1 

3.93 
10.84 

70  1 

Furnaces  12  ft.  in  length,  designed  by  Hosea  Webster,  of  the 
Babcock  &  Wilcox  Co.,  were  used  satisfactorily  for  some  years  in  the 
Waterside  Station  of  the  New  York  Edison  Co.,  with  No.  3  buck- 
wheat coal.  They  were  replaced  by  mechanical  stokers  burning 
semi-bituminous  coal  in  order  to  obtain  greater  capacity  from  the 
boilers. 

The  McClave  Grate  is  shown  in  Fig.  14.  The  rear  section  is  shown 
in  the  usual  position.  The  front  section  is  shown  with  the  bars  tilted 
up  for  breaking  the  clinker. 

Each  row  or  section  of  grate-bars  is  divided  into  a  front  and  rear 
series  by  means  of  two  separate  connecting-bars,  operated  by  twin 
stub-levers  and  connecting-rods,  with  an  operating  handle  adapted  to 
grasp'  either  one  or  both  of  the  levers  in  such  a  manner  that  the  front 
and  rear  series  may  be  operated  separately  or  together.  This  provides 
for  cleaning  out  the  worst  kind  of  clinkers  without  wasting  the  un- 
consumed  fuel  on  the  surface,  as  that  may  be  shoved  over  on  the  sta- 
tionary part  while  the  clinkers  and  ashes  of  the  other  series  are  being 
cut  through  into  the  ash-pit. 

The  McClave  grate  is  extensively  used  for  burning  buckwheat, 
birdseye,  and  other  fine  sizes  of  anthracite  coal.  It  is  also  used  in  the 
coal  regions  for  burning  culm  or  the  refuse  of  the  mines.  Concern- 
ing the  use  of  culm  as  fuel  the  circular  of  the  manufacturers  of  the 
McClave  grate  says : 

"In  the  anthracite  coal-fields  the  waste  product  of  the  mines, 
commonly  called  culm,  has  proved  to  be  a  most  excellent  fuel  for 


206 


STEAM-BOILER  ECONOMY. 


steam  purposes  and  is  now  being  successfully  used  by  the  largest  man- 
ufacturers and  producers  in  the  coal  region. '  The  cost  of  this  fuel  at 
the  mines  is  merely  nominal.,  but  in  order  to  burn  it  successfully  it 
should  contain  at  least  50  per  cent  of  buckwheat  and  should  be  fresh 


FIG.  14. — THE  MCCLAVE  GRATE. 

from  the  mine,  for  when  the  buckwheat  is  nearly  all  screened  out  of 
it,  or  when  it  has  been  exposed  to  the  weather  lor  any  considerable 
length  of  time,  it  is  comparatively  worthless  as  fuel.  Again,  it  will 
not  pay  to  ship  it  any  great  distance,  as  the  freight  on  culm  is  just  as 


FIG.  15. — THE  ARGAND  BLOWER. 


FIG.  16. 


much  per  ton  as  it  is  on  buckwheat  coal,  which,  for  steam  purposes, 
is  a  much  better  fuel  than  culm,  and  costs  at  the  mine  only  from  30 
to  35  cents  per  ton  more  than  culm." 

The  Argand  Steam-blower,  shown  in  Figs.  15  and  16,  is  com- 
monly used  in  connection  with  the  McClave  grate.    It  delivers  a  large 


FURNACES,— METHODS  OF  FIRING,  ETC.  207 

volume  of  air,  mixed  with  steam,  under  the  grate.  The  steam  is 
delivered  to  the  blower  through  a  metal  ring,  perforated  with  small 
holes  on  the  edge  nearest  to  the  ash-pit.  The  jets  of  steam  induce  a 
strong  current  of  air  which  is  blown  under  the  grate.  While  the  use 
of  a  steam- jet  is  usually  the  most  wasteful  method  of  producing  draft, 
it  has  certain  advantages  over  a  dry-air  blast  for  the  burning  of  cheap 
coals  high  in  ash.  The  decomposition  of  the  steam  into  oxygen 
and  hydrogen  by  the  hot  carbon  in  the  bed  of  coal  is  a  cooling  process, 
which  tends  to  prevent  the  formation  of  clinker  on  the  grates.  The 
heat  absorbed  by  this  decomposition  is  again  generated  when  the  gases 
are  burned  in  the  fire-chamber  above  the  grate,  so  that  the  only  losses 
due  to  the  use  of  steam  are  the  cost  of  the  steam  itself  and  the  heat 
required  to  superheat  it  to  the  temperature  of  the  chimney  gases. 

How  to  Burn  Soft  Coal. — Of  all  known  methods  of  burning  soft 
coal  the  worst  is  the  one  which  is  most  commonly  practiced,  viz.,  that 
of  burning  it  in  a  common  furnace,  consisting  of  a  set  of  grate-bars 
and  a  space  of  contracted  dimensions  between  them  and  the  heating 
surface  of  the  boiler,  the  coal  being  fed  by  hand.  This  method  is 
suitable  for  anthracite  coal,  the  smaller  sizes  containing  much  sur- 
face moisture  perhaps  excepted,  but  when  used  for  bituminous  coal  it 
is  objectionable  both  on  account  of  smoke  and  on  account  of  loss  of 
economy.  The  objections  to  the  method  increase  the  farther  we  go 
west  from  the  anthracite  coal-fields  of  Pennsylvania,  being  least  with 
the  semi-bituminous  coals  of  Pennsylvania,  Maryland,  and  Virginia, 
and  increasing  as  wre  go  westward  and  find  the  percentages  of  moisture 
and  of  volatile  matter  both  increasing. 

Objections  to  the  Common  Method. — The  reasons  for  the  difficulty 
in  obtaining  high  economy  from  the  bituminous  coals  when  hand-fired 
in  ordinary  furnaces  may  perhaps  be  understood  if  we  consider  the 
sequence  of  events  that  take  place  between  two  consecutive  firings,  at 
an  interval  of,  say,  five  minutes  apart.  Suppose  that  just  before 
firing  fresh  coal  an  intensely  hot  bed  of  coke,  say  6  inches  deep,  is  lying 
upon  the  grate-bars.  Half  a  dozen  shovelfuls  of  coal,  much  of  it  of 
fine  size,  are  spread  evenly  over  the  bed.  The  first  thing  that  the  fine 
fresh  coal  does  is  to  choke  the  air-spaces  existing  through  the  bed  of 
coke,  thus  shutting  off  the  air-supply  which  is  needed  to  burn  the 
gases  produced  from  the  fresh  coal.  The  next  thing  is  a  very  rapid 
evaporation  of  moisture  from  the  coal,  a  chilling  process,  which  robs 
the  furnace  of  heat.  Next  is  the  formation  of  water-gas  by  the  chem- 
ical reaction,  C  +  H20  =  CO  -f  211,  the  steam  being  decomposed, 


208  STEAM-BOILER  ECONOMY. 

its  oxygen  burning  the  carbon  of  the  coal  to  carbonic  oxide,  and  the 
hydrogen  being  liberated.  This  reaction  takes  place  when  steam  is 
brought  in  contact  with  highly  heated  carbon.  This  also  is  a  chilling 
process,  absorbing  heat  from  the  furnaces.  The  two  valuable  fuel- 
gases  thus  generated  would  give  back  all  the  heat  absorbed  in  their 
formation  if  they  could  be  burned,  but  there  is  not  enough  air  in  the 
furnace  to  burn  them.  Admitting  extra  air  through  the  fire-door  at 
this  time  will  be  of  no  service,  for  the  gases  being  comparatively  cool 
cannot  be  burned  unless  the  air  is  highly  heated.  After  all  the  mois- 
ture has  been  driven  off  from  the  coal,  the  distillation  of  hydrocarbons 
begins,  and  a  considerable  portion  of  them  escapes  unburned,  owing 
to  the  deficiency  of  hot  air,  and  to  their  being  chilled  by  the  relatively 
cool  heating  surfaces  of  the  boiler.  During  all  this  time  great  volumes 
of  smoke  are  escaping  from  the  chimney,  together  with  unburned  hy- 
drogen, hydrocarbons,  and  carbonic  oxide,  all  fuel-gases,  while  at  the 
same  time  soot  is  being  deposited  on  the  heating  surface,  diminishing 
its  efficiency  in  transmitting  heat  to  the  water.  At  length  the  distilla- 
tion of  the  hydrocarbons  proceeds  at  a  slower  rate,  the  very  fine  coal 
which  at  first  obstructed  the  air-supply  is  partially  burned  away,  suf- 
ficient hot  air  comes  through  the  bed  of  hot  coke  to  burn  thoroughly 
all  the  gases,  and  such  a  balance  of  conditions  between  the  amount  of 
gas  generated  and  the  amount  of  air  supplied  exists  that  the  best  pos- 
sible conditions  for  maximum  economy  are  obtained  and  the  chimney- 
gases  are  then  smokeless.  Finally  the  gases  are  all  distilled,  and  a  bed 
of  coke  remains,  which,  as  long  as  it  is  thick  enough  with  relation  to  the 
air-supply,  will  burn  under  good  conditions  for  economy,  but  as  soon 
as  it  burns  down  low  and  the  air-spaces  become  large  enough  to  allow 
an  excessive  supply  of  air  into  the  furnace,  a  new  condition  of  poor 
economy  is  reached,  the  excess  of  air  passing  up  the  chimney  carrying 
away  heat  which  should  have  been  utilized  in  the  boiler. 

The  waste  of  fuel  is  not  the  only  loss  occasioned  by  the  prevalent 
wrongful  method  of  burning  soft  coal.  In  all  western  cities  the  de- 
preciation in  value  of  residence  property  in  the  vicinity  of  factories, 
the  cost  of  painting  and  repainting  of  houses  and  stores,  the  constant 
scrubbing  and  washing  to  remove  soot,  and  the  destruction  of  textile 
fabrics,  if  they  could  all  be  expressed  in  dollars  and  cents,  would 
amount  to  an  enormous  total. 

Smoky  Chimneys  not  Necessary. — All  of  the  loss  due  to  smoky 
chimneys  it  is  quite  possible  to  avoid,  by  the  use  of  well-known  and 
well-tried  appliances.  The  principles  which  govern  the  complete  and 


FURNACES.— METHODS  OF  FIRING,  ETC.  209 

smokeless  combustion  of  bituminous  coal  are  simple  enough,  but  the 
application  of  these  principles  in  practice  has  hitherto  been  usually 
considered  to  involve  extra  cost  of  installation  of  a  boiler  plant,  extra 
cost  of  repairs,  and  extra  trouble.  The  fear  of  extra  cost  and  trouble, 
together  with  exceeding  conservatism  of  factory  owners  in  regard  to 
everything  connected  with  steam-boilers,  have  been  the  chief  obstruc- 
tions to  the  universal  use  of  smokeless  furnaces  in  our  western  States. 
These  obstructions  are,  however,  rapidly  being  removed.  Many  large 
concerns  have  recently  introduced  smokeless  furnaces,  not  to  abate  a 
nuisance,  but  to  save  fuel  and  labor,  and  within  a  very  few  years  it 
may  be  expected  that  their  use  will  be  almost  universal  in  large  boiler 
plants. 

How  to  Avoid  Smoke. — Coal  can  be  burned  without  smoke,  pro- 
vided : 

I.  The  gases  are  distilled  from  the  coal  at  a  uniform  rate. 

II.  'That  the  gases  when  distilled  are  brought  into  intimate  con- 
tact with  very  hot  air. 

III.  That  they  are  burned  in  a  hot  fire-brick  chamber. 

IV.  That  while  burning  they  are  not  allowed  to  come  in  contact 
with  comparatively  cool  surfaces,  such  as  the  shell  or  tubes  of  a  steam- 
boiler;  this  means  that  the  gases  shall  have  sufficient  space  and  time 
in  which  to  burn  before  they  are  allowed  to  come  in  contact  with  the 
boiler  surfaces. 

Mr.  A.  Bement,  Jour.  Western  Soc'y  Engrs.,  1906,  expands  III. 
and  IV.  so  as  to  read : 

"(b)  That  the  gases  which  are  distilled  uniformly  from  the  coal 
shall  enter  a  fire-brick  chamber  of  either  sufficient  length  to  allow 
the  flames  to  become  entirely  consumed  naturally  or  that  the  chamber 
be  provided  with  such  auxiliary  mixing  and  baffling  devices  as  will 
cause  the  gases  to  be  artificially  mixed  together  before  the  exit  of  the 
chamber  is  reached." 

Practical  Success  of  Smoke-prevention. — Mr.  Alfred  E.  Fletcher, 
Chief  Inspector  of  the  Local  Government  Board  in  Scotland,  in  his 
report  for  1892,  says: 

"Consumers  of  coal  in  almost  all  kinds  of  furnaces  have  it  now  in 
their  power  to  conform  with  the  requirements  of  the  Public  Health 
Act,  and  prevent  the  discharge  of  black  smoke  from  their  chimneys. 
As  a  proof  of  this,  one  prominent  instance  can  be  mentioned  of  a 
large  chemical  works,  where  may  be  seen  a  row  of  50  large  Lancashire 
boilers,  each  with  two  furnaces,  and  an  equal  number  of  furnaces 


t 

210  STEAM-BOILER  ECONOMY. 

applied  to  other  purposes  than  that  of  raising  steam,  making  in  all 
as  many  as  200  fires.  Till  lately  a  row  of  four  chimneys  poured  out 
a  mass  of  black  smoke,  which  shrouded  the  whole  district  in  its  pall ; 
now  they  are  smokeless  as  far  as  color  is  concerned,  and  only  fully 
burnt  colorless  gases  are  sent  into  the  air/7 

Progress  in  Smoke  Abatement.* — The  most  direct  evidence  of  the 
improvement  made  in  smoke  abatement  in  recent  years  is  in  the 
record  of  observations  of  atmospheric  conditions  taken  in  many  of 
the  large  cities.  The  "black  fogs"  once  so  prevalent  in  London  and 
which  have  been  proven  to  have  been  due  largely  to  smoke,  are  to-day 
practically  unknown.  The  winter  sunshine  of  London  is  to-day  about 
40  per  cent  of  that  observed  in  the  country  districts,  which  is  a 
figure  double  that  of  30  years  ago.  In  nearly  all  of  the  larger  cities 
a  marked  improvement  along  similar  lines  has  been  made  each  year. 
In  the  manufacturing  districts  the  boiler  users  are  taking  increasing 
interest  in  this  matter,  realizing  that  it  has  an  important  influence 
upon  the  efficiency  of  their  plants.  The  public  is  also  aroused  to 
the  situation  and  the  urgency  and  practicability  of  smoke  abatement 
seem  to  be  generally  appreciated. 

Recognition  was  made  of  the  splendid  work  done  on  smoke 
abatement  in  Cleveland,  Ohio,  and  Chicago,  111.,  where  the  prog- 
ress made  within  the  past  five  years  has  been  remarkable. 

During  the  past  year  the  soot  fall  of  London  has  been  carefully 
measured  by  means  of  specially  devised  soot  gages.  The  total  yearly 
deposit  from  the  atmosphere  was  650  tons  per  square  mile,  or  a  total  of 
76,050  tons  per  annum  for  the  entire  administrative  county  of  Lon- 
don of  117  square  miles.  This  figure  includes  8000  tons  of  sulphates, 
6000  tons  of  ammonia,  and  3000  tons  of  chlorides,  the  balance  being 
carbon  and  tarry  products.  The  deposit  per  square  mile  at  Surrey,  on 
the  border  of  the  metropolitan  area,  was  only  195  tons  per  year,  or  less 
than  one-third  that  of  London  proper,  showing  clearly  the  compara- 
tive purity  of  country  air. 

Smoke  abatement  may  be  best  effected  in  the  present  state  of  the 
art  of  fuel  burning  by  thorough  consideration  of  the  following  con- 
ditions : 

1.  Selection  of  a  suitable  fuel  with  provision  for  maintaining  it 
at  a  fixed  standard  of  heat  value. 

2.  Scientific  study  of  the  conditions  prevailing  in  the  plant,  in- 
cluding draft,  composition  of  gases,  temperatures,  etc. 

3.  Design  or  selection  of  type   of  furnace  or  apparatus  best  adapted 
to  meet  these  conditions. 

4.  Proper  construction  or  installation  of  the  same. 

5.  Careful  selection  of  operating  force. 

6.  Suitable    instrumental    aids    or    guides    for    the    firemen    and 
responsible  engineer. 

*  Extracts  from  a  report  by  George  H.  Perkins  on  the  International  Smoke 
Abatement  Exhibition,  held  in  London,  March,  1912.  Jour.  A.S.  M.  E.,  1912. 


FURNACES.— METHODS  OF  FIRING,  ETC.  211 

7.  Frequent  and  thorough  inspection  to  insure  maintenance  of 
the  highest  possible  efficiency. 

Methods   of   Securing   Complete    Combustion. — The   fundamental 

condition  of  perfect  combustion  of  soft  coal  is  that  every  particle  of 
the  gas  distilled  from  the  coal,,  including  the  water-gas  made  by  de- 
composing its  moisture,  be  brought  in  contact  with  a  sufficient  supply 
of  very  hot  air  to  burn  it,  the  mixing  of  the  gas  and  air  taking  place 
at  a  sufficient  distance  from  the  heating  surfaces  of  the  boiler  so  that 
they  do  not  become  cooled  below  the  temperature  of  ignition  before  the 
combustion  takes  place.  It  is  impossible  to  secure  this  condition  in  an 
ordinary  furnace  with  hand-firing  and  a  level  bed  of  coal. 

It  may  be  secured,  however,  to  a  considerable  extent  with  hand-fir- 
ing if  some  modifications  of  the  furnace  and  of  the  method  of  firing 
are  made.  The  change  required  in  the  furnace  is  the  roofing  of  it 
with  fire-brick  and  the  provision  of  a  large  fire-brick  combustion-cham- 
ber in  which  there  shall  be  sufficient  space  and  time  allowed  for  the 
separate  currents  of  gas  and  of  heated  air  to  become  intimately  mixed 
before  coming  in  contact  with  the  boiler  surfaces. 

The  Coking  System  of  Firing. — The  change  required  in  the  method 
of  firing  is  such  a  change  that  the  whole  bed  of  the  fire  shall  not  at  the 
same  time  be  covered  with  fresh  coal.  To  effect  this,  either  the  coking 
system  or  the  alternate-firing  system  may  be  used.  In  the  first,  or 
coking  system,  the  fresh  coal  is  piled  up  on  the  front  half  of  the  bed 
while  the  rear  half  has  a  level  bed  of  half-burned  coal  upon  it.  The 
gases  distilled  from  the  fresh  coal  then  pass  over  the  rear  half,  through 
which  an  excess  of  air  is  entering,  being  heated  as  they  pass  through 
the  bed  of  coke.  The  two  currents  of  gas,  one  containing  the  distilled 
gases  and  the  other  the  supply  of  hot  air,  intermingle  in  the  hot  com- 
bustion-chamber. When  nearly  all  of  the  gas  has  been  distilled  from 
the  pile  of  coal  in  the  front  half  of  the  furnace,  the  pile  is  pushed  back 
and  levelled  over  the  rear  half,  and  either  immediately  or  within  a 
minute  or  two,  according  to  whether  the  gases  have  been  more  or  less 
completely  driven  off,  fresh  coal  is  again  piled  in  front.  With  some 
coals  the  coking  system  cannot  be  advantageously  used,  namely,  those 
coals  which  contain  a  large  quantity  of  very  fusible  ash.  In  pushing 
back  the  coked  coal  onto  the  rear  of  the  grates,  the  ash  lying  thereon, 
and  which  may  have  been  kept  below  the  fusing  temperature  by  the 
air  passing  through  it,  becomes  mixed  with  the  coked  coal,  which  just 
after  being  pushed  back  burns  with  great  rapidity,  generating  a  very 


212  STEAM-BOILER  ECONOMY. 

high  temperature,  melting  the  ash  and  causing  it  to  run  and  choke 
the  air-spaces  in  the  grate. 

The  coking  system  involves  a  greater  amount  of  labor  and  attention 
on  the  part  of  the  fireman  than  ordinary  level  firing,  and  they  some- 
times object  to  it  on  that  account.  To  what  extent  he  coking  system 
of  firing  will  reduce  the  amount  of  smoke  depends  on  the  character  of 
the  coal,  on  the  skill  of  the  fireman,  and  on  the  size  of  the  fire-brick 
combustion-chamber.  The  lower  the  percentage  of  moisture  and  vola- 
tile matter  the  less  smoke  will  be  made  with  any  system  of  firing,  and 
the  more  complete  will  be  its  suppression  with  the  coking  system. 
The  smaller  the  quantity  of  fresh  coal  fired  at  a  time,  and  the  greater 
the  care  exercised  by  the  fireman  to  keep  the  quantities  fired  each  time 
and  the  intervals  between  firing  uniform,  and  to  keep  the  bed  of  coal 
in  the  rear  level  and  not  too  thick,  the  less  will  be  the  amount  of 
smoke.  The  larger  the  combustion-chamber  in  which  the  currents  of 
smoky  gas  and  of  hot  gas  surcharged  with  air  unite,  the  longer  time 
will  be  afforded  for  their  admixture,  the  more  complete  will  be  the 
combustion,  and  the  less  will  be  the  smoke. 

Alternate  Firing. — A  method  of  firing  which  seems  to  have  all  the 
advantages  of  the  coking  system,  and  none  of  its  disadvantages,  is  that 
known  as  alternate  firing.  It  consists  in  firing  fresh  coal,  first  on  one 
half  of  the  bed  of  the  furnace,  and  then  on  the  other  half,  alternately, 
at  equal  intervals  of  time.  Instead  of  covering  the  whole  bed  with 
fresh  coal,  say  every  ten  minutes,  only  half  the  bed  is  covered  at  each 
firing,  and  the  other  half  is  covered  five  minutes  afterwards.  After 
each  addition  of  fresh  coal  the  volatile  gases  that  arise  from  it  come  in 
contact  with  the  current  of  hot  gas,  carrying  an  excess  of  air,  which 
arises  from  the  half-burned  coal  on  the  other  half  of  the  bed.  In  this 
system  of  firing  the  fresh  coal  may  be  fired  alternately,  either  in  the 
front  and  rear  of  the  bed,  or  on  the  right  and  left  side,  the  former 
being  called  alternate  front  and  back  firing,  and  the  latter  alternate 
side  firing.  With  this  system  of  firing  the  successful  prevention  of 
smoke  depends  largely  on  the  skill  of  the  fireman,  but  more  especially 
on  the  size  of  the  combustion-chamber,  and  the  opportunity  it  affords 
for  thorough  admixture  of  the  two  currents  of  gas.  Baffle-walls  placed 
in  the  combustion-chambers  to  compel  the  gases  to  take  a  circuitous 
direction  facilitate  the  mixture,  and  together  with  the  side  walls  and 
fire-brick  roof,  have  what  is  called  a  regenerative  action,  on  the  prin- 
ciple of  the  Siemens  regenerators,  used  in  steel-melting  furnaces, 
absorbing  heat  during  the  times  when  the  burning  gases  are  the  hot- 


FURNACES.— METHODS  OF  FIRING,  ETC. 


213 


test,  and  giving  out  heat  to  the  gases  when  they  are  cooler,  or  imme- 
diately after  the  firing  of  fresh  coal. 

Alternate  firing  is  of  no  use  unless  there  is  a  large  combustion- 
chamber  in  which  the  two  gaseous  currents  are  mixed  and  the  smoke 
burned  before  they  are  allowed  to  come  in  contact  with  the  heating 
surface. 

The  "Wing-wall"  Furnace. — This  furnace  was  patented  by  the 
author  May  17,  1898.  It  is  adapted  for  the  smokeless  combustion  of 


FIG.  17. — THE  "  WING-WALL  "  FURNACE  APPLIED  TO  A  WATER-TUBE  BOILER. 

soft  coal,  peat,  wood,  tan-bark,  and  other  fuels  that  contain  large  pro- 
portions of  volatile  matter  and  moisture. 

The  drawings,  Fig.  17,  show  the  furnace  applied  to  a  water-tube 
boiler.  C  is  a  fire-chamber  or  oven,  built  of  brick  and  extending  out 
in  front  of  the  boiler.  In  it  the  fuel  is  burned,  either  on  the  ordinary 
grate-bars  or  by  means  of  a  mechanical  stoker.  D  is  an  ordinary 
bridge  wall.  EE'  are  two  tall  vertical  walls  called  wing-walls,  built 


214 


STEAM-BOILER  ECONOMY. 


some  distance  in  the  rear  of  the  bridge  wall.  G  is  a  combustion- 
chamber.  HH  are  several  piers  of  fire-brick,  projecting  into  the 
chamber  G,  from  the  rear  wall  J.  K  is  the  ordinary  partition  wall 
built  across  the  boiler-tubes,  and  M  is  a  tile  roof  to  the  chamber  F  to 
prevent  the  gases  in  that  chamber  from  reaching  the  tubes  until  after 
they  have  passed  through  the  narrow  vertical  passage  between  the 
wing-walls  EE' . 

In  operation  with  hand-firing,  the  alternate  method  of  firing  is 
used.    The  fresh  coal  is  spread  alternately  on  the  right  and  left  sides 


Sectional   Plan  a-b. 

FIG.  18. — THE  "  WING-WALL  "  FURNACE  APPLIED  TO  A  HORIZONTAL  TUBULAR 

BOILER. 

of  the  grate  at  equal  intervals  of  time.  Immediately  after  firing  on 
one  side  dense,  smoky  gases  arise  on  that  side,  while  on  the  other  side 
an  excessive  supply  of  very  hot  air  is  passing  through  the  bed  of  par- 
tially burned  coal  or  coke.  These  two  currents,  one  of  cool,  smoky 
gas  and  the  other  of  clear,  hot  gas  with  a  large  excess  of  air,  pass  side 
by  side  over  the  bridge  wall  D,  but  they  are  compelled  to  change  their 
direction  and  mingle  together  on  passing  through  the  tall  narrow  pas- 
sage between  the  wing-walls  EE',  and  by  so  mingling,  the  gases  are 
burned  and  smoke  is  prevented. 

The  combustion  is  assisted  by  the  heat  radiated  from  the  walls  of 
the  combustion-chamber  G  and  the  piers  H,  which  absorb  heat  dur- 


FURNACES.— METHODS  OF  FIRING,  ETC.  215 

ing  the  time  when  the  fire  is  hottest- — that  is,  just  before  fresh  coal  is 
spread  on  the  grate,  and  give  out  heat  to  the  gases  in  the  chamber  G 
when  the  fire  is  coolest — that  is,  just  after  firing,  when  the  smoky 
gases  are  escaping. 

Fig.  18  shows  a  modification  of  the  furnace  applied  to  a  horizontal 
tubular  boiler  (patented  April  23,  1901).  In  this  arrangement  the 
oven  built  in  front  of  the  boiler  is  dispensed  with,  and  the  space  in  the 
rear  of  the  bridge  wall  is  used  for  a  combustion-chamber.  GG  here 
are  the  wing-walls,  and  II  an  intercepting  wall,  built  so  as  to  prevent 
the  gases  passing  over  the  arch. 

Introduction  of  Heated  Air  into  the  Furnace. — The  admission  of 
heated  air  into  the  furnace,  through  hollow  bridge  and  side  walls  or 
through  channels  in  fire-brick  arches  over  the  furnace,  has  long  been 
a  favorite  method  of  inventors  of  appliances  for  producing  smokeless 
combustion,  and  numerous  patents  have  been  taken  out  for  such  appli- 
ances during  the  last  fifty  years  or  more.  The  theory  of  this  method 
of  improving  combustion  is  correct,  but  it  has  usually  failed  to  come 
into  extensive  use  on  account  of  practical  difficulties.  The  usual 
troubles  are  that  the  air  is  not  made  hot  enough,  that  not  enough  air  is 
introduced  into  the  furnace  at  the  time  when  it  is  needed,  that  is,  just 
after  fresh  coal  has  been  fired,  and  too  much  is  admitted  when  little  or 
none  is  needed,  or  when  sufficient  air  is  passing  through  the  grates. 
The  air-passages  also  are  apt  to  become  clogged  with  dust.  Sometimes 
air  is  forced  into  the  passages  by  means  of  a  steam-jet,  and  some  benefit 
in  diminishing  smoke  is  apparent,  but  a  loss  of  economy  usually  results, 
and  the  use  of  the  jet  is  abandoned.  Automatic  appliances  for  ad- 
mitting air  just  after  firing,  and  shutting  it  off  gradually  during  two 
or  three  minutes  following,  have  also  been  used  sometimes  with  appar- 
ently good  results,  but  they  do  not  appear  to  have  been  generally  suc- 
cessful. Admitting  cold  air  above  the  coal  will  be  of  no  use  to  burn 
these  gases  unless  it  becomes  highly  heated  after  its  admission  by  con- 
tact with  or  radiation  from  the  hot  walls  of  the  furnace  and  combus- 
tion-chamber. AYhen  there  is  a  long  fire-brick  combustion-chamber 
in  the  rear  of  the  furnace  in  which  the  air  and  gases  may  unite,  the 
automatic  admission  of  air  just  after  firing,  and  its  gradual  shutting 
off  may  prove  beneficial  both  in  diminishing  smoke  and  in  improving 
economy. 

Jets  of  steam  are  sometimes  blown  into  the  furnace,  above  the  fire, 
carrying  jets  of  air  with  them,  on  the  principle  of  the  injector.  That 
they  do  decrease  the  amount  of  smoke  in  some  cases  there  seems  to 


216  STEAM-BOILER  ECONOMY. 

be  no  doubt.    Eeasons  which  have  been  given  to  explain  the  action  of 
the  jet  and  which  may  to  some  extent  be  true  are  the  following: 

(1)  The  diminution  of  smoke  is  apparent  and  not  real.    Both  the 
air  and  the  steam  dilute  the  smoke,  and  make  it  less  dense  in  appear- 
ance as  it  escapes  from  the  top  of  the  chimney.    The  steam  also  escap- 
ing from  the  chimney  as  a  white  cloud  disguises  the  smoke  and  may 
condense  its  bulk,  rendering  it  less  visible.    Further,  the  chilling  action 
of  the  air  and  steam  may  decrease  the  rapidity  of  production  of  the 
smoke  in  the  furnace,  extending  its  production  over  a  longer  period  of 
time,  decreasing  its  density  during  that  time. 

(2)  The  jet  of  air  violently  driven  in  by  the  steam  and  pointed 
downwards  onto  the  bed  of  coal,  becomes  intimately  mixed  with  the 
gases  distilled  from  the  coal,  and  then  if  there  is  a  long  run-through 
the  hot  combustion-chamber  the  mixture  will  be  burned,  destroying 
the  smoke. 

The  steam-jet  is  in  itself  a  wasteful  appliance,  for  even  if  the  steam 
is  decomposed  and  the  gases  aterwards  completely  burned,  forming 
steam  again,  it  escapes  from  the  boiler  superheated  to  the  temperature 
of  the  flue  gases,  which  temperature  is  always  higher  than  that  of  the 
steam  in  the  jet,  and  there  is  a  consequent  loss  of  heat  due  to  the 
superheating. 

Tests  of  Steam-jet  Smoke  Preventers.  (J.  A.  Switzer,  Power,  Jan. 
16,  1912).— The  boiler  plant  of  the  Knoxville  Ey.  &  Light  Co., 
consists  of  three  300  H.P.  Stirling  and  five  600  H.P.  Babcock  & 
Wilcox  boilers.  Using  Jellico,  Tenn.,  coal,  hand  fired,  the  smoke 
was  excessive  and  the  efficiency  of  boiler  and  grate  was  only  about 
60%.  After  the  installation  of  a  steam- jet  and  door-closing  device 
it  was  estimated,  from  observations  with  the  Eingelmann  smoke 
chart  that  90%  of  the  smoke  had  been  abated,  and  a  boiler  test  on 
the  Babcock  boilers  gave  an  efficiency  of  77%  when  they  were  driven 
at  85%  of  their  rating. 

The  very  low  efficiency  of  the  boiler  without  the  apparatus  is 
explained  by  the  fact  that  the  boiler  tubes  were  heavily  coated  with 
soot.  Fig.  19  shows  the  relative  appearance  of  the  stacks  before  and 
after  the  use  of  the  apparatus. 

The  smoke-consuming  apparatus  consists  of  a  steam  line  termi- 
nating in  jets  placed  just  inside  the  special  fire  doors  which  are  fitted 
with  dashpots  connected  by  a  lever  system  to  automatically  con- 
trolled valves.  The  arrangement  is  such  that  when  a  door  is  opened 
for  stoking  the  steam  is  automatically  turned  on  and  discharged  into 
the  combustion-chamber.  When  the  door  is  closed  after  firing,  the 
steam  continues  to  blow,  and  dampers  on  the  door  are  held  open  for 


FURNACES.— METHODS  OF  FIRING,  ETC. 


.217 


a  period  of  three  or  four  minutes;  then  the  motion  of  the  dashpot 
slowly  closes  the  dampers  and  throttles  the  steam. 

The  action  in  abating  smoke  is  as  follows :  When  fresh  coal  is 
fired  upon  the  hot  fuel  bed,  the  combustible  volatile  matter  begins  in- 
stantly to  distill  in  great  quantity.  For  the  complete  combustion 
of  this  gas  an  increased  supply  of  air  is  immediately  required.  The 
steam  jets  create  the  draft  and  the  open  dampers  furnish  the  avenue 
for  the  admission  of  this  supply  of  air.  But  in  addition  to  fulfilling 
this  function,  the  jets  by  a  swirling  action  serve  to  bring  about  a 
complete  mixing  of  the  air  and  combustible  gas,  thus  insuring 


FIG.  19. — APPEARANCE  OF  STACKS  BEFORE  AND  AFTER  USE  OF  JETS. 

practically  complete  combustion  before  the  burning  gases  can  come 
into  contact  with  the  heating  surfaces. 

A  Superheated  Steam  Jet. — In  the  Luckenbach  steam  jet  system, 
which  has  been  introduced  to  a  considerable  extent  in  Chicago    (Eng. 


FIG.  20. — FURNACE  WITH  SUPERHEATED  STEAM  JET. 

News,  Dec.  29,  1910),  highly  superheated  steam  issues  as  fine  needle 
jets  from  orifices  located  in  the  furnace  walls  at  a  little  distance 
above  the  fire.  The  effect  of  these  jets,  issuing  from  opposite  sides 
of  the  furnace  at  high  velocity,  is  to  thoroughly  mix  the  combusti- 


218  STEAM-BOILER  ECONOMY. 

ble  gases  rising  from  the  coal  with  the  oxygen  of  the  air.  Steam 
taken  from  the  boiler  is  led  to  a  heavy  cast-ing  built  into  the  bridge 
wall,  as  shown  at  A  in  Fig.  20.  This  casting  contains  a  pipe  coil 
through  which  the  steam  passes  on  its  way  to  the  jets.  A  valve  in 
the  supply  pipe  is  connected  to  a  mechanism  operated  by  the  fire 
door,  so  that  the  valve  is  opened  at  the  same  time  with  the  fire  door 
and  is  automatically  closed  at  a  certain  interval  after  the  fire  door 
has  been  closed.  Thus  the  jets  are  operated  during  the  time  when 
the  fresh  coal  thrown  on  the  fire  is  giving  off  a  large  volume  of 
gases  which  would  appear  as  smoke  if  not  consumed.  After  the 
fire  is  bright,  and  there  is  no  further  need  for  the  mixing  action,  the 
steam  valve  is  closed. 

Downward  Draft  Furnaces. — In  ordinary  hand-fired  furnaces,  fresh 
coal  is  fed  on  top  of  the  bed,  and  the  air  passes  upwards  through  the 
grate,  then  through  the  very  hot  partially  burned  coal  or  coke  lying  on 
the  grate,  and  finally  through  the  fresh  coal  from  which  the  volatile 
gases  are  being  distilled.  If  the  direction  of  the  draft  can  be  reversed, 
the  air  being  admitted  above  the  coal  and  passing  down  through  it  and 
through  the  grate,  the  character  of  the  operation  of  the  furnace  is 
completely  changed.  The  cold  air  and  the  cool  distilled  gases  pass  to- 
gether down  through  the  hot  coke,  and  if  the  air-supply  is  sufficient 
the  gases  will  be  thoroughly  burned  and  smoke  will  be  prevented.  To 
prevent  the  burning  out  of  the  grate-bars  they  are  made  of  water-tubes, 
which  are  connected  by  headers  with  the  boiler  so  as  to  insure  a  positive 
circulation  of  the  water  through  them. 

The  Hawley  Down-draft  Furnace. — This  is  a  form  of  down- 
draft  furnace  which  has  for  more  than  twenty  years  been  widely  intro- 
duced in  the  United  States,  and  has  given  excellent  results  both  in 
smoke-prevention  and  in  economy  of  fuel.  Besides  the  water-grate 
upon  which  the  coal  is  fed,  there  is  a  lower  or  common  grate,  upon 
which  is  burned  the  coke  that  falls  through  the  water-grate.  The 
greater  part  of  the  air-supply  is  admitted  above  the  fresh  coal  on  the 
water-grate,  passing  through  the  coal  and  an  additional  supply  is 
admitted  below  the  lower  grate,  passing  upwards  through  it  to  burn 
the  coke  and  to  assist  in  burning  the  gases.  The  space  between  the 
two  grates  forms  part  of  the  combustion-chamber  in  which  the  gases 
are  burned. 

Fig.  21  shows  a  Hawley  furnace  as  applied  to  a  Heine  water-tube 
boiler  and  Fig.  22  a  view  of  the  water-grate.  The  pipe-connections 
by  which  a  circulation  of  water  is  insured  through  the  water-grate  are 
also  shown  in  Fig.  21. 


FURNACES.— METHODS  OF   FIRING,  ETC. 


219 


Automatic  or  Mechanical  Stokers. — By  the  use  of  mechanical 
stokers  the  chief  objections  to  hand-firing  are  avoided,  viz.,  the  inter- 
mittent supply  of  coal,  the  sudden  volatilization  of  great  volumes  of 


FIG.  21. — HAWLEY  DOWN-DRAFT  FURNACE  APPLIED  TO  A  HEINE  BOILER. 

smoky  gas,  the  alternately  deficient  and  excessive  air-supply,  and  the 
cooling  due  to  frequent  opening  of  the   fire-door.     When   properly 


FIG.  22. — WATER-GRATE  USED  IN  THE  HAWLEY  FURNACE. 

designed  and  operated  these  stokers  feed  both  the  coal  and  the  air 
at  a  regular  rate,  and  when  the  air  and  the  coal-supply  are  properly 
adjusted  to  each  other,  and  proper  provisions,  such  as  a  fire-brick 


220  STEAM-BOILER  ECONOMY. 

combustion-chamber  or  other  means,  are  made  for  compelling  the 
currents  of  gas  and  air  to  become  completely  intermingled,  they  will 
burn  coal  without  smoke  and  at  same  time  with  the  maximum 
economy  which  the  design  and  proportions  of  the  boiler  permit.  More- 
over, in  large  plants  they  are  capable  of  effecting  a  great  saving  of 
labor,  especially  when  they  are  used  in  conjunction  with  modern 
methods  of  storing  coal  in  overhead  bins  and  feeding  it  by  gravity 
through  chutes  into  the  hoppers  of  the  stoker.  The  chief  objection 
to  them  is  their  initial  first  cost.  In  large  well-designed  plants,  how- 
ever, this  objection  is  to  a  great  extent,  if  not  entirely,  overcome  by 
the  fact  that  when  the  stokers  and  their  rate  of  driving  are  properly 
proportioned  to  the  boilers,  it  is  possible  to  obtain  from  a  boiler  con- 
siderable increase  of  capacity  compared  with  hand-firing,  without  any 
sacrifice  of  economy,  and  therefore  the  number  of  boilers  required 
may  be  less  than  with  hand-firing. 

Advisability  of  Installing  Stokers. — The  cost  of  stokers  is  greatly 
in  excess  of  the  cost  of  hand-fired  furnaces.  The  upkeep  cost  of 
the  furnace  is  greater  than  in  hand-fired  practice.  From  their  greater 
first  cost  and  the  more  severe  nature  of  the  service,  the  depreciation 
will  be  greater  than  in  the  case  of  hand -fired  furnace  material. 

Automatic  stokers  require  a  higher  degree  of  intelligence  on  the 
part  of  the  operating  crew  than  do  hand-fired  furnaces,  but  such 
an  objection  is  largely  overcome  by  the  present-day  tendency  toward 
the  employment  of  a  better  class  of  labor  in  the  boiler  room.  An 
early  objection  to  stokers  in  general  had  its  basis  in  the  fact  that 
the  ash  contained  an  excessive  amount  of  unburned  carbon.  This 
objection  also  has  been  largely  overcome  by  improvements  in  design 
of  practically  all  stokers. 

The  question  of  the  advisability  of  a  stoker  installation  is  one 
which  must  be  considered  most  carefully  in  all  of  its  phases.  The 
added  efficiency  and  capacity,  the  labor  saving  possible,  and  the 
smokelessness  must  be  balanced  against  the  added  first  cost  or  in- 
terest on  the  investment,  the  depreciation  and  maintenance  cost, 
the  steam  required  for  stoker  drive  or  blast,  and  the  added  cost  of 
furnace  upkeep.  In  general,  a  stoker  installation  will  be  found 
profitable  in  the  larger  plants  properly  equipped  for  handling  the 
fuel  and  ashes.  In  small  plants  such  an  installation  may  be  advis- 
able only  where  the  question  of  smokeless  combustion  is  paramount. 
•  (From  Babcock  &  Wilcox  Co.'s  book  on  Chain  Grate  Stokers.) 

Types  of  Mechanical  Stokers. — The  stokers  now  in  common  use 
may  be  divided  into  four  general  classes,  depending  on  the  kind  of 
mechanism  used  for  feeding  the  coal.  In  the  first  class  the  coal  is 


FURNACES.— METHODS  OF  FIRING,  ETC. 


221 


carried  on  grate-bars,  either  horizontal  or  inclined  more  or  less,  the 
individual  bars,  or  sometimes  alternate  bars,  being  given  a  reciprocat- 
ing to  and  fro,  up  and  down,  or  rocking  motion,  by  which  the  coal  is 
gradually  advanced  along  the  grates.  In  the  second  class  the  grate  is 
steeply  inclined,  and  the  coal  is  pushed  onto  its  upper  end,  and  slides 
down  slowly  as  it  burns.  In  the  third  class  the  whole  grate  forms  an 
endless  chain  of  short  bars,  on  which  the  coal  travels  horizontally  into 
the  furnace,  the  chain  passing  over  a  sprocket-wheel  at  the  end  and 
returning  through  the  ash-pit.  In  the  fourth  class  the  fresh  coal  is  fed 
in  underneath  the  burning  coal,  and  the  gases  distilled  from  it  pass 
through  the  bed  of  hot  coke  above,  the  action  being  exactly  the  reverse 
of  that  of  the  Hawley  down-draft  furnace,  in  which  the  fresh  coal  is 
fed  on  the  top  of  the  bed,  and  the  gases  pass  down  through  the  bed  of 
hot  coke  beneath.  A  brief  description  of  some  modern  forms  of 
stokers  will  now  be  given. 


Longitudinal    Section. 

FIG.  23. — THE  PLAYFORD  STOKER. 


The  Chain-grate  Stoker. — Fig.  23  shows  the  Playford  stoker.  To 
the  travelling-chains  are  attached  a  series  of  wrought-iron  T  bars,  run- 
ning across  the  furnace,  and  these  carry  the  small  cast-iron  sections 
of  which  the  grate  is  made.  Below  the  chain-grate  a  screw-conveyor 


222 


STEAM-BOILER  ECONOMY. 


is  placed  for  carrying  the  ashes  forward  from  the  rear  of  the  furnace 
to  the  ash-pit  in  front. 

The  Babcock  &  Wilcox  Stoker,  Fig.  24,  is  also  an  endless-chain 
grate.  It  has  been  used  with  much  success  in  the  West  with  bitu- 
minous coals.  The  cut  shows  the  stoker  removed  from  the  furnace. 
It  is  driven  by  a  worm-wheel,  the  power  being  delivered  to  the  worm 
from  an  independent  engine  through  a  lever  and  ratchet-wheel.  The 


FIG.  24. — THE  BABCOCK  &  WILCOX  STQKER. 


large  vertical  pipe  is  the  coal-feeder,  which  delivers  coal   from  the 
overhead  'bin  into  the  hopper. 

Notes  on  Chain  Grate  Stokers.  (Discussion  of  a  Paper  read  be- 
fore the  Cleveland  Engineering  Society,  Indust.  Eng.,  Nov.  1913). — 
When  chain-grate  stokers  are  used  the  coal  should  be  crushed  so  that 
85  to  90  per  cent  will  pass  through  a  %x%-in.  screen. 

Chain  grate  stokers  to  properly  handle  coking  coals  must  have 
an  ignition  arch  of  proper  construction  so  that  the  coal  is  coked  before 
it  leaves  the  forward  end  of  the  arch.  To  better  accomplish  this 
uniform  ignition,  instead  of  using  sprung  arches,  flat  arches  are  now 
generally  installed.  These  give  a  better  distribution  of  the  gases 
across  the  furnace,  as  the  gases  do  not  have  the  tendency  to  draw  to  the 
center  that  they  have  when  a  sprung  arch  is  used.  Where  coals 
coke  readily  under  the  ignition  arch  a  crust  forms  which  cuts  off 
the  proper  air  supply,  but  with  non-coking  coals  there  is  little  trouble 


FURNACES— METHODS  OF  FIRING,  ETC.  223 

from  this  crusting  over,  and  the  air  supply  at  this  point  is  not  so 
much  interfered  with. 

To  provide  a  sufficient  air  supply  under  the  ignition  arch  when 
a  coking  coal  is  used,  air  has  been  introduced  through  a  row  of  small 
openings  in  the  arch  above  the.  coal  just  as  it  leaves  the  hopper,  result- 
ing in  diminished  smoke  and  increased  economy. 

Joseph  Harrington  described  a  "reflecting  arch/'  a  long  or  inclined 
arch  so  placed  that  the  heat  from  the  rear  or  incandescent  portion 
of  the  fuel  bed  is  directly  reflected  to  the  incoming  fuel  at  the  gate. 

Its  height  and  inclination  render  it  possible  to  utilize  for  ignition 
purposes  the  direct  radiation  from  the  face  of  the  bridge  wall.  It 
is  of  the  utmost  value  even  though  it  may  be  anywhere  from  nine 
to  twelve  feet  away  from  the  gate.  By  means  of  this  type  of -arch 
setting,  great'  intensity  of  ignition  effect  prevails  and  a  rapidity  of 
combustion  may  be  secured  thereby  which  is  difficult  or  impossible  with 
certain  other  types  of  settings.  Satisfactory  ignition  with  grate  speeds 
up  to  10  or  12  inches  a  minute  can  readily  be  attained,  which  cor- 
responds to  a  rate  of  combustion  exceeding  50  pounds  per  square 
foot.  These  high  rates  can  only  be  attained  with  fuel  bed  thicknesses 
which  will  permit  of  the  application  of  high  draft.  All  of  the  con- 
ditions which  produce  high  efficiency  may  be  present  in  a  plant,  but 
if  left  to  the  eye  they  will  not  be  effectively  ~used.  Instruments  of 
precision  are  absolutely  required,  such  as  a  recording  draft  gage  in 
the  furnace  and  at  the  damper,  a  C02  chart,  and  a  recording  ther- 
mometer in  the  uptake.  It  is  only  by  the  careful  watching  of  such 
instruments  that  the  entire  plant  can  be  operated  at  anywhere  near 
the  maximum  efficiency.  D.  S.  Jacobus  stated  that  in  European 
chain-grate  practice,  air  is  often  admitted  at  the  front  of  the  stoker. 
In  some  cases  the  air  is  pre-heated.  Air  admitted  in  this  way  reduces 
the  smoke  and  careful  gas  analyses  and  station  records  have  shown 
that  if  the  proper  amount  of  air  is  used,  there  is  no  falling  off  in 
the  economy.  The  chart  illustrating  the  falling  off  in  economy  with 
different  percentages  of  C02  shows  that  the  proportionate-  gain'  in 
maintaining  C02  higher  than  12  per  cent  is  not  as  great  as  by  in- 
creasing the  percentage  from  a  lower  amount  of  C02  to  this  figure.  If 
an  increase  in-the  amount  of  C02  above  12  per  cent  is  accompanied 
by  the  formation  of  carbon  monoxide,  the  gain  will  be  less  than 
shown  by  the  chart.  With  no  CO  present,  12  per  cent  of  CO, 
is  just  as  favorable  an  analysis  for  economy  as  14%  C02  with  0.3% 
of  CO.  Often  in  making  gas  analyses  a  small  amount  of  CO  will 
not  be  detected.  In  obtaining  the  highest  efficiencies  it  is  of  great 
importance  to  accurately  measure  the  CO,  which  can  be  done  more 
surely  by  using  a  Hempel  apparatus,  where  the  gas  is  shaken  up 
with  the  solution,  than  by  using  an  Orsat  apparatus. 

Tile  Roof  Setting  with  Transverse  Gas  Passages. — Fig.  25  shows  a 
setting  designed  by  A.  Bement  for  the  Cedar  Rapids  (Iowa)  City 
Railway  and  Light  Co.,  and  described  by  him  in  the  Journal  of  the 


224 


STEAM-BOILER  ECONOMY. 


Western  Society  of  Engineers,  1908.  It  was  designed  for  highly 
volatile  Western  coals  and  has  given  excellent  results.  Mr.  W.  J. 
Greene  of  the  Cedar  Eapids  Co.  says  of  it  after  15  months  service: 
When  this  boiler  was  installed  for  us,  in  addition  to  the  fear  that 
the  circulation  of  the  water  would  be  reversed,  many  persons  sug- 


FIG.  25. — TILE  ROOF  AND  TRANSVERSE  PASSAGES. 

gested  other  difficulties  that  would  be  encountered,  namely :  that 
explosive  gases  would  collect  in  the  first  passage  just  under  the  drums 
and  when  mixed  with  air  coming  through  the  fire  would  explode, 
causing  damage  to  brick-work;  that  dust  would  collect  in  the  open 
spaces  between  the  first  and  second  rows  of  tubes  so  rapidly  as  to 


rmTTTTTTTTTTTTTTTTTTTTT 


FIG.  26. — FAILURE  OF  IGNITION  ARCH. 

seriously  cut  down  the  draft  or  cause  much  extra  work  to  keep  the 
dust  removed;  and  that  the  baffle  walls  could  not  be  kept  in  place. 
None  of  these  troubles  have  been  encountered.  As  to  the  dust,  with 
the  exception  of  a  small  accumulation  at  the  front  water  legs  and 
first  baffle,  the  passage  is  kept  clear  by  the  draft  and  requires  no 
cleaning.  The  baffle  walls  have  given  no  trouble  whatever- 

In  the  discussion  of  Mr.  Bement's  paper  the  author  criticised  a 
minor  feature   of  the   setting,   the  extension   of  the   arch  over  the 


FURNACES— METHODS  OF  FIRING,  ETC. 


225 


fire  into  a  region  where  it  was  surrounded  entirely  by  intensely  hot 
gases,  and  Mr.  Bement  replied  as  follows: 

Professor  Kent's  criticism  of  the  extension  of  the  ignition  arch 
so  far  into  the  furnace  is  excellent,,  and  his  prediction  that  it  would 
burn  out  shows  excellent  judgment,  because  this  is  just  what  did  hap- 
pen to  it.  After  it  had  been  in  use  for  something  like  two  months, 
it  failed  by  settling  down  in  the  center  as  shown  by  Fig.  26.  There 
is  really  no  occasion  for  such  a  long  arch,  because  a  corresponding 
effect  may  be  obtained  from  the  presence  of  the  tile  furnace  roof. 

The  Honey  Mechanical  Stoker. — This  stoker  was  first  brought  out 
in  1885.  The  present  construction  is  shown  in  Fig.  27.  It  receives 


FIG.  27. — THE  HONEY  MECHANICAL  STOKER. 


the  fuel  in  bulk,  and,  without  further  handling,  feeds  it  continuously 
and  at  any  desired  rate  to  the  furnace,  burns  the  combustible  portion 
and  deposits  the  ash  and  clinker  in  the  ash-pit  ready  for  removal. 

In  the  bottom  of  the  coal-hopper  is  located  a  sliding  pusher,  which 
gradually  feeds  the  coal  over  the  dead-plate  and  on  to  the  grate.  The 
latter  consists  of  horizontal  flat  surfaced  overlapping  bars,  extending 


226  STEAM-BOILER  ECONOMY. 

from  side  to  side  of  the  furnace,,  and  inclined  at  an  angle  of  37  de- 
grees'from  the  horizontal.  In  the  wider  furnaces  two  or  more  sets  of 
grate-bars  are  placed  side  by  side,  provided  with  independent  actuating 
connections.  The  grate-bars  rock  in  unison,  assuming  alternately  a 
stepped  and  an  inclined  position.  When  they  rock  forward  into  the 
inclined  position  the  burning  coal  tends  to  work  down  in  a  body,  but 
before  it  can  move  too  far  the  bars  rock  back  to  the  stepped  position, 
checking  the  downward  motion,  breaking  up  the  bed  of  fuel  and  freely 
admitting  air  through  the  fire.  This  alternate  starting  and  checking 
motion  keeps  the  fire  constantly  stirred  and  opened  up  from  beneath, 
and  finally  lands  the  cinder  and  ash  on  the  dumping-grate,  from  which 
it  is  discharged  into  the  ash-pit.  The  depending  webs  of  the  grate- 
bars  are  perforated  with  longitudinal  slots,  so  placed  that  the  condi- 
tion of  the  fire  can  be  seen  at  all  times  and  free  access  had  to  all  parts 
of  the  grate  without  the  opening  of  doors.  These  slots  also  serve  to 
furnish  an  abundant  supply  of  air  for  combustion.  The  motion  of  the 
grate-bars  and  the  feeding  device  is  regulated  by  two  simple  adjust- 
ments, by  which  the  action  of  the  stoker  is  controlled  and  the  fires 
are  forced,  checked  or  banked  at  will. 

A  coking-arch  of  fire-brick  is  sprung  across  the  furnace,  covering 
the  upper  part  of  the  grate  and  forming  a  gas-producer  whose  action 
is  to  coke  the  fresh  fuel  and  release  its  gases,  which,  mingling  with 
heated  air,  supplied  in  small  streams  through  the  perforated  tile  above 
the  dead-plate,  are  burned  in  the  large  combustion-chamber  above  the 
bed  of  incandescent  coke  on  the  lower  part  of  the  grate. 

This  stoker  burns  all  kinds  of  coal,  from  lignite  to  anthracite,  and 
also  waste  products,  such  as  tanbark,  sawdust,  cottonseed  hulls,  and 
coke  "breeze,"  without  change  of  grate-bars. 

The  Murphy  Automatic  Furnace  is  shown  in  cross-section  as  ap- 
plied to  a  horizontal  tubular  boiler  in  Fig.  28.  The  furnace  is  also 
applicable  to  all  forms  of  fire-tube  and  water-tube  boilers.  The 
grates  are  of  a  "V"  form  and  in  pairs,  the  upper  ends  resting  on  the 
magazine  bed-plate,  which  is  also  the  feed-  or  coking-plate,  while  the 
lower  ends  rest  in  niches  on  the  grate-bearer,  which  also  contains 
the  clinker-bar  or  clinker-breaker.  A  fire-brick  arch  is  sprung  across 
the  furnace,  covering  the  grate-surface,  and  on  top  of  each  side  of  the 
arch  there  is  an  air-flue  from  which  hot  air  is  supplied  through  the 
series  of  small  openings  at  the  bases  of  the  arch  where  the  brick  rests 
on  the  ribbed  surface  of  the  arch-plates  on  either  side  of  the  furnace. 
This  gives  a  double  side  feed-  and  coking-plate.  The  coal  magazines 


FURNACES.— METHODS  OF  FIRING,  ETC. 


227 


are  provided  with  stoker-boxes,  which  are  connected  by  means  of  pin- 
ion-gears to  the  stoker-shaft,  which  is  automatically  moved  back  and 
forih,  stoking  the  coal  into  the  furnace.  One  grate  of  each  pair  of 
grates  is  fixed,  while  the  other  is  movable  up  and  down  by  a  rocker 
motion  at  the  lower  or  center  end,  thus  keeping  the  fire  free  from 
ashes  while  the  coarse  refuse  and  clinker  is  worked  down  to  the  center, 
where  a  rotating  clinker-bar  grinds  it  into  the  ash-pit.  The  entire 
operating  mechanism  is  attached  to  a  flat  iron  bar  running  across  the 
outside  of  the  front,  and  operated  by  a  little  automatic  upright  engine 
set  at  the  corner  of  the  setting,  which  uses  about  one  horse-power  per 


FIG.  28. — THE  MURPHY  AUTOMATIC  FURNACE. 

furnace  operated.  Each  revolution  of  the  driving-gear  stokes  a  given 
but  variable  quantity  of  coal  into  the  furnace  on  each  side,  moves  half 
of  the  grate-bars  on  each  side  up  and  down,  and  turns  the  clinker-bar 
partly  around.  Thus  the  coal  is  fed  and  the  fires  cleaned  constantly. 
The  teeth  on  the  clinker-bar  are  prevented  from  becoming  hot  and 
worn  off  by  means  of  a  current  of  air  passing  through  the  open  center 
of  the  bar  and  piped  to  the  flue  or  stack  beyond  the  damper. 

The  clinker  is  kept  brittle  and  prevented  from  sticking  by  a  spray 
of  exhaust  steam  distributed  through  a  pipe  cast  into  either  side  of 
the  grate-bearer. 

The  Jones  Under-feed  Stoker  (Figs.  29  and  30)  was  patented  in 
1896  by  E.  W.  Jones  of  Portland,  Oregon.  The  fresh  coal  is  pushed 


228 


STEAM-BOILER  ECONOMY. 


up  through  the  bed  of  burning  fuel  by  means  of  a  steam-ram,  oper- 
ated by  a  hand-lever  connected  to  a  valve,  by  means  of  which  the 
charges  of  fuel  can  be  delivered  as  required.  Air  at  about  four 
ounces  pressure  is  forced  through  the  tuyere-blocks,  and  up  through 
the  heap  of  burning  fuel,  and,  mingling  with  gases  from  the  coking 
coal,  produces  an  intense  and  rapid  combustion.  Owing  to  the  large 


FIG.  29. — THE  JONES  UNDER-FEED  STOKER. 


I.I. I , L 


J L 


FIG.  30. — CYLINDER  OF  THE  JONES  STOKER. 

excess  of  air  delivered  at  high  pressure,  and  its  thorough  mingling 
with  the  gases,  a  practically  smokeless  combustion  is  obtained.  This 
stoker  has  been  principally  used  with  low-grade  Western  American 
bituminous  slack  coal. 

The  "Taylor"  Gravity  Underfeed  Stoker. — Fig.  31  is  a  develop- 
ment of  the  underfeeding  principle  of  the  Jones  Stoker.  It  differs 
from  that  stoker  in  that  the  retorts  or  fuel  magazines  are  inclined, 
permitting  the  ashes  formed  on  the  surface  of  the  fuel  bed  to  be  dis- 


FURNACES.— METHODS  OF  FIRING,  ETC. 


229 


posed  of  at  the  rear  or  bridge-wall  end  of  the  furnace,  instead  of  at 
the  sides  of  the  retorts.  The  coal  descending  from  the  hopper  is 
pushed  forward  by  an  upper  plunger  into  the  fuel  magazine,  a  space 
between  two  adjoining  tuyere  or  inclined  air  boxes.  A  lower  plunger 
working  in  the  bottom  of  the  fuel  magazine  with  an  adjustable  stroke 
pushes  the  green  and  partially  coked  fuel  toward  the  bridge-wall  and 
assists  the  ash  down  the  inclined  fuel  surface.  The  partially  consumed 
coke  and  ashes  gradually  descend  onto  an  extension  overfeed  grate  and 
thence  on  to  a  dump  plate  at  the  rear  of  the  stoker,  as  illustrated,  or  in 


FIG.  31. — THE  TAYLOR  GRAVITY  UNDERFEED  STOKER. 

some  cases  onto  an  automatic  ash  discharge  and  crusher.  Here  the 
mixed  coal  and  ashes  are  allowed  to  remain  for  a  sufficient  length  of 
time  to  consume  the  larger  portion  of  the  combustible.  The  speed  of 
the  rams  and  the  rate  of  fuel  are  so  arranged  as  to  maintain  a  depth 
of  from  18  to  30  inches  of  fuel  bed  above  the  tuyeres. 

The  tuyeres  consist  of  cast-iron  plates  with  horizontal  passages 
which  deliver  the  air  horizontally  into  the  coal  as  it  travels  out  of 
the  mouth  of  the  fuel  retorts.  The  cut  shows  some  of  the  plates  re- 
moved. 

Fig.  31  shows  a  view  from  the  bridge-wall  of  a  large  stoker  con- 
sisting of  seven  fuel  magazines  or  retorts,  each  equipped  with  an  upper 


230 


STEAM-BOILER  ECONOMY. 


and  lower  plunger.  The  upper  and  lower  plungers  are  driven 
through  connecting  rods  from  a  slowly  revolving  crank-shaft.  The 
crank-shaft  is  in  turn  driven  through  two  trains  of  worm  gearing. 
Each  gear  box  or  set  of  gears  drives  a  maximum  of  four  retorts.  The 
speed  shafts  of  the  gear  box  are  connected  through  chains  and  shaft- 
ing to  the  shaft  of  a  volume  blower. 

The  blower  is  arranged  to  run  at  a  variable  speed,  its  operation 
being  automatically  controlled  by  the  demands  for  steam.  Any 
change  in  the  speed  of  the  blower  results  in  a  change  in  the  flow  of 
air  delivered  and  in  a  change  in  the  rate  of  fuel  feeding,  so  that  a 
constant  ratio  of  fuel  fed  to  air  supplied  is  maintained.  The  fix- 
ing of  the  ratio  between  the  air  and  coal  is  determined  by  analyzing 
continuous  samples  of  flue  gas. 

Results  of  tests  on  boilers  equipped  with  Taylor  stokers  will  be 
found  in  a  later  chapter. 


FIG.  32. — THE  RILEY  SELF-DUMPING  UNDERFEED  STOKER. 


The  Riley  Self-dumping  Underfeed  Stoker  is  of  the  inclined  under- 
feed type,  that  is,  the  coal  is  forced  up  from  beneath  the  point 
where  the  air  is  admitted,  and  then  is  worked  along  toward  the 
bridge  wall.  Instead  of  stationary  dead  plates,  it  has  moving  air- 


FURNACES.— METHODS  OF  FIRING,  ETC. 


231 


supplying  grates,  carried  by  the  reciprocating  sides  of  the  retorts, 
and  also  moving  overfeed  grates,  extending  across  the  entire  width  of 
the  stoker.  Beyond  these  are  pushers  for  continuously  dumping  the 
refuse.  The  travel  of  these  reciprocating  parts  is  adjustable  so  as 
to  control  the  movement  of  the  fuel  bed  and  dumping  of  refuse.  Fig. 
32  is  a  longitudinal  cross-section,  and  Fig.  33  a  view  from  the  bridge- 
wall  of  a  five-retort  stoker. 

The  incline  of  the  retorts  and  grates  is  so  slight  that  the  fuel 
bed  does  not  move  except  as  it  is  mechanically  propelled.     Eecipro- 


FIG.  33. — THE  RILEY  STOKER. 


cation  of  alternate  retort  sides  in  opposite  directions  keeps  the 
coal  in  motion  slowly  along  the  incline,  distributing  it  evenly. 

This  reciprocating  action  is  the  distinctive  feature  of  this  stoker 
and  causes  an  action  in  the  fuel  bed  somewhat  different  from  that 
in  any  other  type  of  underfeed  stoker.  There  is  a  more  or  less 
well  defined  slicing  action  along  the  lines  between  adjacent  retort 
sides.  This  serves  to  keep  clinkers  broken  up  and  furnishes  a  ready 
exit  for  hot  gases  which  might  otherwise  have  a  destructive  re- 
verberatory  action  under  large  clinkers. 

The  upper  edges   of  the   reciprocating   retort  sides   carry   grate 


232  STEAM-BOILER  ECONOMY. 

blocks,  which  are  really  narrow  grates  with  side  tuyere  openings 
for  allowing  air  to  enter  the  green  fuel  below  the  zone  of  combus- 
tion. These  grate  blocks  are  baffled  so  that  while  they  allow  air 
to  escape  freely,  they  do  not  allow  fuel  or  ashes  to  sift  through  into 
the  air  chamber  below.  Beyond  the  end  of  the  underfeed  retorts 
the  overfeed  grates  of  the  same  type  extend  the  entire  width  of 
the  retorts.  The  air  for  the  overfeed  grates  is  less  in  pressure 
than  the  underfeed  air,  and  is  at  all  times  under  the  control  of  the 
operator. 

The  reciprocating  motion  of  the  retort  sides  and  of  the  overfeed 
grates  produce  a  continuous  movement  along  the  slope  to  the  pusher 
noses  which  push  the  refuse  slowly  back  toward  the  bridge  wall  until 
it  drops  through  the  opening.  The  dumping  capacity  of  the  stoker 
is  equal  to  the  displacement  of  the  pusher  noses,,  and  this  is  regu- 
lated by  the  amount  of  travel  given  to  the  retort  sides,  which  is 
adjusted  in  proportion  to  the  percentage  of  ash  in  the  fuel.  The 
dump  is  continuous  and  automatic,  after  allowing  the  refuse  time 
enough  to  become  thoroughly  burned  out  and  practically  cold.  The 
ash  pit  is  in  a  separate  compartment  which  need  have  no  communi- 
cation with  the  fire-room. 

The  stoker  and  its  forced  draft  fan  are  coupled  together  so  that  the 
ratio  of  air  to  fuel  remains  constant,  no  matter  how  the  load  fluctuates. 
The  proper  ratio  of  fan  and  stoker  speed  is  fixed  from  flue  gas 
analysis.  This  regulator  ratio  is  never  changed  unless  there  is  a 
radical  change  in  the  kind  of  fuel. 

Mechanical  Stokers  for  Locomotives. — Several  forms  of  stoker 
have  been  tried  on  American  locomotives,  and  two  of  them,  the  Craw- 
ford underfeed  and  the  Street  overfeed,  appear  to  have  given  fairly 
satisfactory  results  as  to  developing  the  fullest  capacity  of  the  locomo- 
tive boiler.  Thirty  of  the  Street  stokers  were  in  operation  and  69 
under  construction,  as  a  result  of  the  good  performance  of  the  30, 
in  1912.  (See  report  of  a  committee  of  the  Am.  Ey.  Mast.  Mechs. 
Assn.,  1912,  Eng.  News,  June  27,  1912.) 

Burning  Illinois  Coals  without  Smoke. — Prof.  L.  P.  Brecken- 
ridge  describes  in  Bulletin  15  of  the  University  of  Illinois  Engineer- 
ing Experiment  Station  a  series  of  tests  of  four  types  of  water-tube 
boilers  with  different  kinds  of  stokers,  to  determine  the  rate  at 
which  the  boiler  could  be  driven  without  making  smoke.  The  follow- 
ing table  shows  the  principal  results : 


FURNACES.— METHODS  OF  FIRING,  ETC. 


233 


Rated 

Per  cent  Rated 

No. 

Type  of 
Boiler. 

Stoker. 

Baffling. 

Capacity. 

Capacity 
without 

Smoke. 

1 

B.  &W. 

Chain  grate 

Vertical 

150 

50  to  120 

2 

Stirling 

ii         (  ( 

Usual 

260 

50  to  140 

3 

National 

{  (         1  1 

Vertical 

250 

50  to  120 

4 

B.  &W. 

Roney 

'< 

220 

up  to  100 

5 

i  i 

1  1 

Horizontal 

220 

50  to  100 

6 

Stirling 

Stirling 

Usual 

260 

50  to  140 

7 

Heine 

Chain  grate 

Horizontal 

210 

50  to  140 

NOTES. — In  No.  4  there  is  only  a  short  arch  over  the  stoker,  and  the  bottom 
row  of  tubes  is  not  protected  by  fire-brick.  This  unit  when  handled  carefully 
can  be  run  up  to  capacity  without  smoke  above  No.  2  on  the  Ringlemann  chart. 
It  requires  careful  attention  and  at  capacities  above  100%  cannot  be  run 
without  objectionable  smoke  except  by  expert  firemen.  No.  5  is  the  same 
as  No.  4  except  that  there  is  a  tile  roof  furnace  and  baffling  parallel  to  the 
tubes.  It  can  be  run  from  50  to  100%  of  capacity  without  smoke. 

No.  2  has  the  chain-grate  covered  for  nearly  its  whole  length  with  fire-brick 
arches,  and  has  a  very  large  combustion-chamber.  It  operates  easily  without 
smoke  at  capacities  from  50  to  140%. 

No.  7  can  be  run  easily  at  from  50  to  140%.  It  is  almost  impossible  to 
make  smoke  with  this  setting  under  any  condition  of  operation.  The  setting 
is  shown  in  Fig.  34. 

The  tests  above  described  were  all  with  water-tube  boilers.  In 
the  same  Bulletin  Prof.  Breckenridge  discusses  the  problem  of  burn- 
ing Illinois  coals  without  smoke  under  fire-tube  boilers  as  follows: 


FIG.  34. — A  SMOKELESS  FURNACE. 


The  horizontal  fire-tube  boiler  is  still  much  in  use  in  smaller 
units  of  50  to  150  H.P.  With  Illinois  coals  carrying  30  to  40  per 
cent  of  volatile  combustible  matter  and  burned  at  rates  which  pro- 
duce flame  lengths  of  from  5  to  20  feet,  there  is  no  better  method 
of  producing  dense  black  smoke  than  to  install  a  horizontal  fire-tube 


234  STEAM-BOILER  ECONOMY. 

boiler  with  the  usual  furnace,  and  hand-fire  such  a  plant  with  a  run- 
of-mine  coal.  The  method  of  introducing  the  coal  directly  into 
the  hot  furnace,  in  fine  dust  and  large  lumps.,  prevents  slow  or 
uniform  di3tillation  of  the  gases;  the  air  supply  through  open 
doors,  through  holes  in  the  fire,  or  through  a  fuel  bed  of  varying 
thicknesses  is  neither  correct  in  quantity  nor  is  much  of  it  properly 
heated ;  the  mingling  products  of  combustion  come  in  contact  with  the 
cool  surface  of  the  plates  of  the  boiler,  reducing  the  temperature  of 
the  gases  below  the  ignition  temperature  before  combustion  is  com- 
pleted. 

It  is  possible  to  burn  Illinois  coal  without  smoke  with  fire-tube 
boilers,  but  the  furnace  requires  special  treatment.  The  plans  usually 
proposed  are  either  low-set  stokers  or  extended  Dutch  oven  furnaces. 
When  hand-firing  is  adopted  the  wing-wall  furnace  or  other  form  of 
mixing  baffles  or  piers  is  of  great  assistance.  With  any  of  these  de- 
vices careful  firing  is  very  necessary  for  satisfactory  results.  The 
best  method  of  hand-firing  for  smokelessness  is  also  the  best  for  attain- 
ing economy.  There  are  three  generally  recognized  methods  of  hand- 
firing:  (a)  The  Spreading,  (6)  The  Coking,  and  (c)  The  Alternate. 
The  first  is  satisfactory  for  anthracite;  the  second  for  coking  coals 
and  the  last  for  non-coking  coals.  It  is  the  alternate  method  that 
is  best  suited  to  Illinois  coals.  This  method  is  described  as  follows: 
The  fuel  bed  area  is  divided  into  equal  parts,  two,  four,  or  six,  depend- 
ing on  the  size  of  the  entire  surface.  The  fresh  coal  is  fired  alternately 
on  one-half  of  these  areas  at  a  time  at  such  intervals  as  may  be 
necessary  to  hold  the  steam  pressure.  Depending  on  the  rate  of 
driving,  these  intervals  will  vary  from  one  to  five  minutes.  When 
the  fuel  bed  area  is  very  large,  some  checker-board  system  of  firing 
may  be  adopted  which,  when  alternately  fired  and  left  free  for  air 
passage,  will  result  in  a  large  reduction  in  the  amount  of  smoke 
produced  by  the  too  common  method  of  spreading  the  coal  over  the 
entire  surface  at  each  firing.  It  may  be  advantageous  to  provide 
for  still  more  air  by  leaving  the  fire  doors  open  slightly  just  after 
each  firing.  There  are  several  devices  on  the  market  which  provide 
for  an  air  supply  over  the  fire,  which  are  turned  on  with  the  open- 
ing or  closing  of  the  fire  door  and  which  can  be  arranged  to  close 
at  the  end  of  any  desired  time,  depending  upon  the  rate  of  driving 
and  frequency  of  firing  found  desirable.  The  firing  of  small  amounts 
of  coal  at  frequent  intervals  produces  less  smoke  than  firing  large 
amounts  at  longer  intervals.  The  latter  method,  however,  usually 
proves  less  tiresome  to  the  fireman  and  is  for  that  reason  more  fre- 
quently adopted. 

Forced  Draft. — The  use  of  forced  draft,  as  a  substitute  for,  or  as  an 
aid  to,  natural  chimney  draft,  is  becoming  quite  common  in  large 
boiler-plants.  Its  advantages  are  that  it  enables  a  boiler  to  be  driven 
to  its  maximum  capacity  to  meet  emergencies  without  reference  to  the 


FURNACES.— METHODS  OF  FIRING,  ETC.  ,     235 

state  of  the  weather  or  to  the  character  of  the  coal;  that  the  draft 
is  independent  of  the  temperature  of  the  chimney  gases,  and  that 
therefore  lower  flue  temperatures  may  be  used  than  with  natural  draft ; 
and  in  many  cases  that  it  enables  a  poorer  quality  of  coal  to  be  used 
than  is  required  with  natural  draft. 

Forced  draft  may  be  obtained :  First,  by  a  steam- jet  in  the  chimney, 
as  in  locomotives  and  steam  fire-engines ;  second,  by  a  steam- jet  blower 
under  the  grate-bars;  third,  by  a  fan-blower  delivering  air  under  the 
grate-bars,  the  ash-pit  doors  being  closed;  fourth,  by  a  fan-blower  de- 
livering air  into  a  closed  fireroom,  as  in  the  "closed  stokehold"  sys- 
tem used  in  some  ocean-going  vessels ;  and  fifth,  by  a  fan  placed  in  the 
flue  or  chimney  drawing  the  gases  of  combustion  from  the  boilers, 
commonly  called  the  induced-draft  system.  Which  one  of  these  several 
systems  should  be  adopted  in  any  special  case  will  usually  depend  on 
local  conditions.  The  steam- jet  has  the  advantage  of  lightness  and 
compactness  of  apparatus,  and  is  therefore  most  suitable  for  locomo- 
tives and  steam  fire-engines,  but  it  also  is  the  most  wasteful  of  steam, 
and  therefore  should  not  be  used  when  a  fan-blower  system  is  available, 
except  for  occasional  or  temporary  use,  or  when  very  cheap, fuel,  such 
as  anthracite  culm  at  the  coal-mines,  is  used. 

The  closed  stokehold  system  has  as  yet  been  used  only  in  marine 
practice,,  where  it  has  some  advantage,  such  as  ventilation  of  the  fire- 
room,  over  the  closed  ash-pit  system.  Induced  draft  has  been  used  to 
some  extent  on  land,  with  good  results,  but  it  does  not  appear  to  have 
any  especial  advantage  over  the  closed  ash-pit  system,  except  conven- 
ience of  application  in  some  situations,  as  where  an  exhaust-fan  can  be 
placed  in  the  chimney  more  easily  than  a  fan-blower  of  sufficient  size 
can  be  accommodated  in  the  boiler-  or  engine-room.  In  a  crowded  and 
poorly  ventilated  fire-room  a  fan-blower  delivering  air  under  the  grates 
and  maintaining  a  pressure  of  gas  in  the  furnace  may  sometimes  cause 
objectionable  gases  and  dust  to  issue  into  the  fireroom,  and  in  such  a 
case  induced  draft  may  be  preferable. 

When  an  economizer  is  used  to  absorb  some  of  the  heat  escaping 
from  the  boilers,  it  is  generally  advisable  to  use  forced  draft,  since  the 
lower  temperature  of  the  gases  discharged  from  the  economizer  reduces 
the  force  of  draft  in  the  chimney,  and  the  friction  of  the  gas  passages 
through  the  economizer  itself  reduces  the  force  of  draft  at  the  boiler. 

Forced  draft  is  especially  valuable  in  large  boiler-plants,  such  as 
those  of  electric  light  and  power  stations,  where  the  demand  for  steam 
is  much  greater  during  a  few  hours  in  the  day  than  during  the  rest 


236  STEAM-BOILER  ECONOMY. 

of  the  time.  A  boiler-plant  which  would  be  insufficient  with  natural 
draft  to  supply  the  steam  required  during  the  hours  of  heaviest  load, 
may  be  able  to  supply  it  with  ease  by  the  aid  of  forced  draft. 

When  forced  draft  is  used,  it  is  advisable  to  provide  it  with  auto- 
matic regulation,  the  delivery  of  steam  to  the  engine  driving  the  fan 
being  regulated  by  a  reducing-  valve,  or  a  cut-off  valve,  controlled  by 
the  pressure  in  the  boiler,  as  in  the  Beckman  system.  This  system 
consists  of  a  fan-blower,  driven  by  a  small  engine,  delivering  air  into  a 
conduit  built  under  the  bridge  wall,  which  conduit  may  be  common  to 
a  battery  of  boilers,  and  thence  through  openings  into  the  ash-pit 
under  the  grate  of  each  boiler.  In  the  steam-pipe  leading  to  the  en- 
gine there  are  three  valves.  The  first  automatically  opens  or  closes  as 
the  steam-pressure  falls  or  rises.  The  second  is  a  reducing- valve  which 
delivers  to  the  engine  steam  of  the  pressure  required  to  drive  the  en- 
gine at  the  right  speed  for  furnishing  the  air  to  burn  the  particular 
kind  of  fuel  used.  The  third  is  a  by-pass  valve  which -lets  enough 
steam  into  the  engine  while  the  first  valve  is  closed  to  keep  the  engine 
just  moving  and  furnishing  enough  air  to  keep  the  grates  cool.  The 
damper  leading  from  the  air-conduit  into  the  ash-pit  is  closed  when 
the  boiler  is  out  of  use  or  during  cleaning. 

The  Effect  of  Damper  Regulation. — To  obtain  maximum  economy 
of  a  steam  boiler  during  a  test  at  a  given  rate  of  driving  it  is 
important  that  the  rate  be  kept  as  nearly  constant  as  possible.  If 
it  is  allowed  to  fluctuate  there  will  be  a  difficulty  in  adusting  the 
air  supply  and  the  thickness  of  the  bed  of  coal  so  as  always  to  have 
the  best  furnace  conditions.  If,  therefore,  the  demand  for  steam 
from  the  boiler  plant  varies,  assuming  there  are  other  boilers  in  it 
besides  the  one  being  tested,  it  is  well  to  let  the  fluctuations  be 
taken  care  of  by  the  other  boilers,  checking  their  draft  or  closing 
their  dampers  when  the  pressure  rises  and  increasing  their  draft 
when  it  fails,  so  that  the  boiler  under  tesl;  may  continue  to  be  driven 
at  a  steady  rate.  In  regular  practice,  however,  it  is  customary  to 
take  care  of  the  fluctuations  in  the  steam  demand  and  supply  by 
means  of  a  damper  regulator  which  controls  the  draft  in  the  main 
flue,  or  in  the  case  of  forced  draft  by  a  regulator  that  controls  the  rate 
of  driving  of  the  fan  or  blower. 

Draft  Loss  through  a  Vertical  Pass  Water-tube  Boiler. —  (T.  A. 

Marsh,  Indust.  Eng.,  July,  1912.) 


FURNACES.— METHODS  OF  FIRING,  ETC. 


237 


Draft  in  furnace 0 . 50  in. 

Draft  above  first  row  of  tubes,  front  upward  pass '0.53 

Draft  above  twelfth  row  of  tubes,  front  upward  pass 0 . 58 

Draft  above  twelfth  row  of  tubes,  middle  downward  pass 0 . 62 

Draft  above  first  row  of  tubes,  middle  downward  pass 0 . 82 

Draft  above  first  row  of  tubes,  rear  upward  pass 0.85 


0.05  loss 


0.20  loss 


Draft  above  twelfth  row  of  tubes,  rear  upward  pass 0 . 98 

Draft  in  flue,  just  beyond  damper 1 .00 


0.13  loss 


The  increase  in  draft  loss  through  the  second,  or  downward,  pass 
is  due  to  its  restricted  area,  as  compared  with  the  first  pass.  In  the 
third  pass  the  temperature  and  volume  of  the  gas  are  greatly  reduced, 
which  accounts  for  the  draft  loss  being  less  than  in  the  second  pass. 

Arrangement  of  Forced  Draft  Apparatus. — Fig.  35  illustrates  the 
arrangement  of  forced  draft  apparatus  at  the  power  station  of  the 
Hudson  &  Manhattan  E.  R.  Co.  in  Jersey  City,  N".  J.,  which  operates 


FIG.  35. — ARRANGEMENT  OF  FORCED  .DRAFT  APPARATUS. 

the  railroad  through  tunnels  under  the  Hudson  river.  The  air  flue 
shown  serves  the  batteries  of  boilers  on  both  sides  of  the  boiler  room. 
The  fan  is  a  double  inlet  "Sirocco,"  driven  by  a  500  H.P.  electric 
motor,  and  its  normal  duty  is  209,000  cubic  feet  of  air  per  minute 
at  4.9  ins.  water  gauge. 

Economy  of  High  Rates  of  Driving  at  Peak  Loads.— (H.  G. 
Stott,  Power,  November  8,  1910.)  In  the  boiler  room  the  invest- 
ment can  be  kept  down  by  adding  grate  surface  instead  of  more 
boilers,  and  by  the  use  of  forced  draft  the  old  rating  of  10  sq.  ft. 
of  heating  surface  per  boiler  horsepower  can  safely  be  reduced  to  4 


238 


STEAM-BOILER  ECONOMY. 


or  5  without  materially  adding  to  the  cost  of  boiler  or  furnace  main- 
tenance. 

While  the  overall  boiler  efficiency  will  begin  to  fall  off  beyond 
175  or  200  per  cent  of  rating,  the  small  loss  thus  entailed  is  insignifi- 
cant compared  to  the  saving  in  fixed  charges. 

The  solution  of  the  problem  of  carrying  peak  loads  economically 
is  therefore  to  be  found  in  reducing  the  investment  per  kilowatt  to 
a  minimum,  and  this  can  be  best  accomplished  at  present  by  the 
use  of  steam  turbines  and  by  the  use  of  large  grate  area,  such  as  a 
ratio  of  30  or  40  sq.  ft.  of  heating  surface  to  each  square  foot  of  grate 
area,  instead  of  the  present  ratio  of  55  or  60  to  1. 

Relation  of  Draft  to  Boiler  Capacity.— Fig.  36  is  a  plotted  chart 
showing  the  furnace  draft  and  the  flue  gas  temperatures  in  eleven 


ID 

I. 

|2 
0 

o 

§§  Flue  gas 
25  5  temperature 

/ 

/ 

V 

^ 

^ 

I/ 

0 

^ 

j. 

0 

^ 

^ 

Ox 

/o 

o^nV 

e  x' 

X 

pX 

o 

i^ 

.?-e- 

•^ 

~r 

^ 

-^ 

-/' 

9- 



.—• 

-'• 

'•""" 

^ 

^ 

^^^n* 

^ 

^ 

G 

-"""" 

350  400 


500 


600          700          800          900         1000 
Capacity  in  boiler  horse-power 


1100        1200 


FIG.  36.— RELATION  BETWEEN  BOILER  CAPACITY  AND  FURNACE  DRAFT. 
tests  of  the  Green  chain  grate  stoker.    (Proc.  Western  Soc.  of  Engrs., 
1912.)     The  draft  curve  shows  an  interesting  relation  between  the 
horsepower  and  the  draft;  it  is  that  the  horsepower  is  nearly  pro- 
portional to  the  square  root  of  the  draft  pressure,  as  follows : 


Draft,  ins  

0  5 

1 

2 

3 

4 

K 

VD.  . 

0  71 

1 

1  41 

1  73 

2 

9  94. 

H.P  

420 

570 

750 

905 

1015 

1  10A 

H.P.^VZ) 

590 

570 

532 

523 

cjOS 

^00 

If  the  resistance  of  the  fuel  bed,  the  air  per  pound  of  carbon, 
and  the  boiler  efficiency  were  the  same  at  all  rates  of  driving,  the 


FURNACES.— METHODS  OF  FIRING,  ETC. 


239 


horsepower  should  theoretically  vary  directly  as  the  square  root  of  the 
draft  pressure,  but  in  fact  there  is  usually  an  increased  resistance 
at  the  higher  rates  of  driving  on  account  of  increase  in  the  thickness 
of  the  fuel  bed,  an  increase  in  the  volume  per  pound  of  furnace 
gas  on  account  of  the  increased  temperature  of  the  gas  between  the 
furnace  and  the  flue,  and  a  decrease  in_  efficiency,  all  of  which  will 
cause  a  decrease  in  the  ratio  HP  -r-  V D. 

The  Prat  Induced  Draft  System.  (Louis  Prat,  Paris;  Schiitte 
&  Koerting  Co.,  Philadelphia)  has  been  extensively  introduced  in 
Europe.  Only  a  small  portion  of  the  gases 
is  passed  through  the  fan,  which  is  therefore 
of  relatively  small  bulk.  The  pressure  pro- 
duced by  the  fan  is  used  in  the  manner  of 
the  impulse  jet  of  an  ejector  to  create  the 
necessary  negative  pressure  for  the  induction 
of  the  gases.  The  system  is  illustrated  in 
Fig.  37.  It  includes  a  metal  plate  stack  com- 
parable to  an  ejector  of  which  C  is  the  con- 
verging portion,  A  the  chamber  and  B  the 
diffuser.  The  negative  pressure  inducing  the 
flow  of  the  gases  is  created  by  a  fluid  im- 
pulser  furnished  by  a  fan-blower  and  injected 
into  the  chamber  by  the  nozzle  D.  In  case 
of  a  stoppage  of  the  fan  the  impulse  is  pro- 
duced by  an  emergency  steam  ejector  8.  The 
fluid  impulser  can  either  be  cold  air  taken  by 
the  fan  from  outside  or  the  hot  gases  directly 
from  the  flue  as  shown  in  the  illustration. 

The  Howden  Hot-air  System. — In  1884  James  Howden  applied  to 
the  boilers  of  the  City  of  New  York  a  forced  draft  apparatus  in 
which  the  air-supply  was  heated  by  being  circulated  around  a  series 
of  tubes,  through  which  the  hot  flue-gases  passed  on  their  way  to 
the  stack.  In  this  system  part  of  the  hot  air  is  delivered  into  the  ash- 
.pit,  and  part  above  the  bed  of  coal  in  the  furnace.  The  system  has 
been  extensively  adopted  in  marine  practice.  Among  the  advantages 
claimed  for  it  are :  1.  Part  of  the  heat  which  would  otherwise  escape  in 
the  flue-gases  is  returned  to  the  boiler.  2.  By  whatever  amount  the  air 
for  combustion  is  increased  in  temperature  by  the  waste  gases,  the 
average  temperature  of  the  furnaces  is  practically  raised  to  the  same 
extent.  If,  say  200°  is  added  to  the  air  of  combustion  by  the  air-heat- 


FIG.  37.— PRAT  INDUCED 
DRAFT  SYSTEM. 


240  STEAM-BOILER  ECONOMY. 

ers,  the  average  temperature  of  the  furnaces  is  raised  200°,  and  the 
evaporative  power  of  the  heating  surface  is  thereby  increased.  3.  The 
gases  from  the  burning  fuel  combine  more  readily  with  the  oxygen  of 
the  air  of  combustion  as  the  temperature  of  the  fire  increases. 

Ket  aiders. — In  connection  with  the  Howden  system,  spiral  strips 
of  metal,  shown  in  Fig.  38,  are  placed  in  the  tubes  of  the  boiler. 


FIG.  38. — A  RETARDER. 

These  compel  the  gases  to  take  a  spiral  motion  in  passing  through  the 
tubes,  causing  them  to  come  more  directly  in  contact  with  the  sur- 
face of  the  tubes,  and  by  conducting  heat  through  the  metal  of  the 
retarder  into  the  metal  of  the  tubes,  increasing  their  efficiency. 

Results  of  tests  of  a  horizontal  fire-tube  boiler  with  and  without 
retarders  are  given  in  a  paper  by  J.  M.  Whitham  in  Trans.  A.  S.  M.  E., 
vol.  xvii.  p.  450.  Among  his  conclusions  are  the  following : 

1.  Eetarders  show  an  economic  advantage  when  the  boiler  is  pushed, 
varing  in  the  tests  from  3  to  18  per  cent. 

2.  Eetarders  should  not  be  used  when  boilers  are  run  very  gently 
and  when  the  stack-draft  is  small. 

The  Ellis  &  Eaves  Hot-air  System  is  similar  to  Howden's,  but  the 
draft  is  produced  by  a  fan  placed  at  the  base  of  the  funnel.  The  air 
is  heated  by  being  passed  through  the  tubes  in  the  heater,  while  the 
hot  gas  circulates  around  them.  Both  the  Howlen  and  the  Ellis  & 
Eaves  systems  are  illustrated  and  discussed  at  length  in  Bertin  & 
Robertson  on  "Marine  Boilers." 

An  extensive  series  of  experiments  on  the  use  of  warm  blast  was 
made  .by  J.  C.  Hoadley  in  1881,  and  described  at  great  length  in 
Trans.  Am.  Soc.  M.  E.,  vol.  vi.  p.  676.  The  results,  according  to  Mr. 
Hoadley,  showed  a  possible  net  saving  of  from  10  to  18  per  cent  over 
the  best  attainable  practice  with  natural  chimney  draft  and  air  at 
ordinary  atmospheric  temperatures.  Notwithstanding  these  results, 
the  warm-blast  system  has  not  as  yet  made  any  headway  in  land 
practice. 

Calculations  for  Forced  Draft. — In  designing  a  forced  draft  in- 
stallation the  principal  data  needed  are:  1,  The  maximum  number 
of  pounds  of  coal  that  will  have  to  be  burned  per  hour  at  the  most 
rapid  rate  of  driving,  when  the  efficiency  of  the  boiler,  furnace 


FURNACES.—  METHODS  OF  FIRING,  ETC.  241 

and  grate  is  lowest;  2,  the  number  of  pounds  of  air  per  pound  of 
coal. 

A  pure  coal  consisting  of  95  per  cent  C,  5  per  cent  H  would 
require  for  complete  combustion,  theoretically,,  per  pound  of  coal, 

34.56^  +  H  --  j)  ............    12.672  Ibs.  aii 


Add  50%  in  order  to  insure  that  all  the  C  is  burned 

to  C02.  .  6.356  "     " 


19.008  "     " 

Add  another  50%  for  emergencies  and  for  unskillful 
firing.  (This  may  be  omitted  if  mechanical 
stokers  and  CO2  apparatus  are  used.) 6.336  "  " 

25.344  "     " 

Or  say  25  pounds  of  air  per  pound  of  combustible.  Multiplying  this 
figure  by  the  ratio  of  combustible  to  total  coal  (including  ash  and 
moisture)  in  the  coal  to  be  used  gives  the  number  of  pounds  of  air 
per  pound  of  coal.  Thus,  if  the  sum  of  moisture  and  ash  in  a  given 
coal  is  20  per  cent,  and  the  combustible  80  per  cent,  then  0.80  X 
25  =  20  is  the  number  of  pounds  of  air  required  per  pound  of  coal. 
This  may  be  reduced  to  15  pounds  in  large  plants  in  which  mechanical 
stokers  are  used  and  the  firing  is  controlled  so  as  to  avoid  excessive 
air  supply,  by  means  of  gas  analysis  or  C02  apparatus. 

Multiplying  i he  figures  given  above  by  13.342,  the  number  of  cubic 
feet  per  pound  of  air  at  70°  F.,  gives  the  cubic  feet  of  air  per  pound 
combustible  —  254  cubic  feet  for  50  per  cent  excess  air,  or  338  cubic 
feet  for  100  per  cent  excess. 

It  is  common  to  figure  the  air  supply  as  a  factor  of  the  boiler 
horsepower  to  be  developed.  The  method  of  making  the  calculation 
with  different  kinds  of  fuel  is  shown  in  the  table  on  page  242. 

These  figures  are  based  on  actual  boiler  horsepower  to  be  de- 
veloped (1  H.P.  =  34.5  pounds  water  evaporated  from  and  at  212° 
per  hour)  and  not  upon  the  "rating"  of  the  boiler.  In  modern 
electric  power  plants  it  is  not  uncommon  to  drive  the  boilers  during 
the  time  of  "peak  loads"  to  from  two  to  three  times  their  nominal 
rating,  which  is  usually  based  on  10  square  feet  of  heating  surface 
per  horsepower. 

For  induced  draft  the  figures  of  cubic  feet  of  air  per  minute  given 


242 


STEAM-BOILER  ECONOMY. 

ANALYSIS   OF    COMBUSTIBLE   IN   COAL 


Kind  of  Coal. 

Anthracite. 

Semi-bit. 

Eastern 
Bit. 

Western 
Bit. 

Lignite. 

Oil. 

H.. 
C...    . 

3.16 

9220 

4.76 

9070 

5.03 
8489 

5.41 
8093 

5.05 
7321 

13 

85 

o  

272 

2  81 

7.34 

11  18 

18  65 

N  

098 

1.13 

1.74 

1  61 

1  47 

1       2 

S.. 

0.94 

0.60 

1.00 

0.87 

1.62 

LBS.  AIR  PER  LB.  COMBUSTIBLE  =  34.56(C/3+H—  O/8),  WITH  NO  EXCESS  AIR. 

|     11.59      i     11.97      |     11.20      |     10.71      |     9.37        |     14.20 

B.T.U.    PER   LB.    COMBUSTIBLE. 

|     15,000    |    15,800    I    15,200    |    14;400    |    12,800    |    19,000 


BOILER   EFFICIENCY,    ESTIMATED. 

0.75     I       0.75     |       0.75     |       0.70     |       0.60 


0.75 


B.T.U.    UTILIZED    PER   LB.    COMBUSTIBLE. 

|  11,250  |  11,850  I  11,400  |  10,080  |   7,680  |  14,250 

LBS.  COMBUSTIBLE  PER  HOUR  PER  BOILER  H.P.     (1  H.  P.  =33,479  B.T.U.  PER  HOUR.) 

|       2.98     |       2.83     |       2.94     |       3.32     |       4.36     |       2.35 

LBS.  AIR  PER  BOILER  H.P.  HOUR,  ASSUMING  NO  EXCESS  AIR. 

•      |     34.54     |     33.88     |     32.93     |     35.56     |     40.85     |     33.37 

CU.FT.  OF  AIR  PER  MINUTE  AT  70°  F.  PER  BOILER  H.P.     (1  LB.  AIR  =  13.342  CU.FT.) 


No  excess  air.  . 

7.682 

7.535 

7.323 

7.909 

9.085 

7.422 

50%  "       " 

11.52 

11.30 

10.99 

11.86 

13.63 

11.13 

100%"       " 

15.36 

15.07 

14.65 

15.82 

16.17 

14.84 

above  are  multiplied  by  the  ratio  of  the  absolute  temperature  of  the 
gas  to  be  handled  by  the  fan  to  the  absolute  temperature  correspond- 
T  +  460 


ing  to  70°  F.,  or  by 


530 


,  in  which  T  is  the  temperature  of  the 


gas  in  Fahrenheit  degrees,  to  obtain  the  number  of  cubic  feet  of  hot 
gas  per  minute. 

For  T=        250°  300°         350°        400°         450°        500°         550°     600°     650 

Ratio  (T  +460)/530       1.340         1.434        1.528        1.623        1.717        1.811       1.906       2       2.094 

The  American  Blower  Co.  furnishes  the  following  as  the  basis  for 
calculation  for  mechanical  draft : 


FURNACES.— METHODS  OF  FIRING,  ETC.  243 

MECHANICAL    DRAFT    IN    STATIONARY    WORK. 

Induced  Draft. 

Cu.  ft.  per  min.  required :    36  cu.  ft.  per  min.  per  boiler  horsepower 

per  hour  at  550°  F. 
Suction   required :      For   rated   capacity   1    in.   water   gauge,   static 

pressure;  for  25%  overload  1*4  in.;    for 

50%  overload  1%  in. 
Gases  handled:    482.7  cu.  ft.  at  550°  F.  per  Ib.  coal  burned. 

Forced  Draft. 

Cu.  ft.  per  min.  required :    28  cu.  ft.  per  min.  at  70°  per  boiler  horse- 
power with  chain  grates;  21  cu.  ft.  with 
ordinary  grates;  18  cu.  ft.  with  underfeed 
stokers. 
Pressure  required :    Stokers,  2.5  in.  water  gauge,  static,  not  including 

duct  friction. 

Ordinary  grates:     1.5  in.  water  gauge,  static,  but  allowance  of  suf- 
ficient power  to  speed  up  to  1%  in. 

Where  the  fan  blows  directly  into  the  ash  pit  without  ducts 
1.25  in.  static  water  gauge  will  not  be  exceeded  with  ordinary 
rate  of  coal  combustion. 
Air  handled:    253.5  cu.  ft.  at  70°  F.  per  Ib.  coal  burned. 

MECHANICAL   DRAFT   IN    MARINE    WORK. 

Induced  Draft  (Ellis  &  Eaves  system). 

Cu.  ft.  per  min.  required :     8.05  cu.  ft.  per  min.  at  550°  per  Ib.  coal 

burned  per  hour. 

Suction  required:    1*4  to  1%  in.  water  gauge  (negative  pressure). 
Gases  handled :    482.7  cu.  ft.  at  550°  F.  per  Ib.  coal  burned. 

Forced  Draft  (Howden  system). 

Cu.  ft.  per  min.  required:    4.2  cu.  ft.  per  min.  at  70°  F.  per  Ib.  coal 

burned  per  hour. 

Pressure  required  at  fan:    2y2  to  3  in.  water  gauge  (static  pressure). 
Air  handled :    253.5  cu.  ft.  at  70°  F.  per  Ib.  coal  burned. 

The  Buffalo  Forge  Co.  in  its  Engineers'  Hand  Book,  p.  85,  gives 
the  following: 


244  STEAM-BOILER  ECONOMY. 

It  is  customary  in  practice  in  selecting  apparatus  for  mechanical 
draft  purposes  to  allow  for  100  per  cent  excess  air  for  hand-fired 
boilers,  or  16.70  cubic  feet  of  air  per  minute  at  70°  per  boiler  H.P. 
for  a  forced  draft  fan,  and  32.40  cubic  feet  per  minute  at  550°  for 
an  induced  draft  fan.  An  allowance  of  50  per  cent  excess  air  is 
made  where  the  boiler  is  equipped  with  a  stoker,  or  11.70  cubic  feet 
per  minute  at  70°  per  boiler  H.P.  for  a  forced,  and  22.80  cubic  feet 
per  minute  at  550°  for  an  induced  draft  fan. 

The  statement  made  in  the  catalogues  of  some  fan  manufacturers 
to  the  effect  that  with  forced  draft  less  air  is  used  per  pound  of  coal 
than  with  chimney  draft,  and  that,  therefore,  with  forced  draft  there 
is  a  higher  temperature  in  the  furnace  and  less  loss  of  heat  in  the 
flue  gases,  is  erroneous.  With  forced  draft  it  is  possible  to  make  a 
greater  difference  in  pressure  between  the  ash  pit  and  the  combustion 
chamber  than  with  ordinary  chimney  draft,  and  this  would  tend  to 
increase  the  air  supply  rather  than  to  diminish  it  if  the  thickness 
of  the  fire  bed  were  not  increased  to  counteract  this  effect.  With 
either  forced  draft  or  chimney  draft  it  is  equally  easy  to  reduce  the 
air  supply  to  18  pounds  per  pound  of  coal,  notwithstanding  the  fol- 
lowing statement  which  has  been  reprinted  for  many  years  without 
reference  to  any  authority: 

Experiments  made  by  the  United  States  Navy  have  demon- 
strated that  in  the  ordinary  hand-fired  furnace  with  stack  draft 
about  twice  the  theoretical  quantity  of  air  is  required,  or  about 
24  pounds  of  air  per  pound  of  bituminous  coal. 

When  the  number  of  cubic  feet  per  minute  and  the  total  difference 
in  pressure  between  the  fan  and  the  combustion  chamber  are  deter- 
mined or  estimated  for  the  maximum  rate  of  driving,  then  a  selection 
of  the  fan  to  be  used  is  made,  referring  to  the  tables  of  size,  capacity, 
speed,  pressure,  and  power,  which  are  published  in  the  catalogues 
of  fan  manufacturers.  The  American  Blower  Co.  gives  the  following : 

The  requirements  of  a  given  installation  can  usually  be  met  by 
several  sizes  of  fans,  and  the  final  choosing  of  the  fan  will  depend  upon 
whether  initial  cost,  the  cost  of  power,  or  space,  is  most  important. 
The  following  examples  will  illustrate  the  variation  in  the  sizes  of 
"Sirocco"  fans  for  a  given  duty.  Assume  that  the  installation  requires 
66,000  cubic  feet  of  air  per  minute  at  1%  inches  water  gauge  static 
pressure,  and  that  the  tip  speed  of  the  fan  wheel  shall  not  exceed 
3500  feet  per  minute.  Referring  to  the  capacity  tables  the  following 
performances  will  be  found: 


FURNACES.— METHODS  OF  FIRING,  ETC. 


245 


Single  inlet  fan  No 14  13  12 

Cubic  feet  per  minute 66,000  67,000  65,500 

Revolutions  per  minute 155  170  •              190 

Tip  speed,  feet  per  minute 3,410  3,480  3,590 

Brake  horse-power 27.9  29.5  31.4 

Diam.  of  wheel,  ins 84  78  72 

Width  of  wheel,  ins 42  39  36 

If  power  consumption  is  the  controlling  feature,  the  No.  14  fan 
would  be  the  choice;  if  initial  cost  or  space  limitation  determines 
the  selection,  the  No.  13  fan.  As  the  tip  speed  of  the  No.  12  fan 
slightly  exceeds  the  specified  amount,  it  cannot  be  considered. 

Furnaces  for  Burning  Coal-dust.— Fig.  39  shows  a  coal-dust 
sToker  patented  in  1895  by  F.  De  Camp  of  Berlin,  Germany.  The 


FIG.  39. — METHOD  OF  BURNING  COAL-DUST. 

coal  is  ground  in  a  mill  and  carried  to  the  hopper  of  the  stoker  by  a 
travelling  conveyor,  from  which  it  is  delivered  into  the  furnace  by  a 
fan-blast.  The  quantity  of  coal-dust  as  well  as  the  quantity  of  air 
blown  into  the  furnace  is  regulated  by  slides.  The  advantages  claimed 
for  the  apparatus  are  that  it  is  an  automatic  stoker  and  forced-draft 
system  combined,  and  that  the  combustion  is  complete  and  smokeless. 

The  objections  are,  the  cost  of  power  for  grinding  the  coal  into  a 
fine  powder  and  for  driving  the  fan,  together  with  the  extra  labor  re- 
quired to  keep  the  flues  clean,  on  account  of  the  large  accumulation  of 
ash  and  partially  burned  coal-dust  which  is  carried  over  by  the  blast. 

The  Wegener  Apparatus  for  Burning  Powdered  Coal. — Fig.  40 
shows  an  apparatus  for  burning  powdered  coal,  invented  by  Carl 
Wegener,  and  first  used  in  Germany  in  1892.  It  is  described  as  fol- 
lows: 

Coal  ground  so  that  it  will  pass  through  a  sieve  of  125  me$hes  per 
linear  inch  is  fed  into  the  hopper,  whence  it  falls  on  to  a  fine  sieve 


246 


STEAM-BOILER  ECONOMY. 


about  5J  in.  diameter.  The  sieve  is  tapped  from  150  to  250  times  a 
minute,  in  order  to  cause  the  coal  to  fall  through  it  regularly,  by 
means  of  a  knocker  on  a  vertical  shaft  driven  by  a  wheel  placed  in 
the  path  of  the  entering  air-supply.  The  air  ascending  in  the 
inlet-pipe,  as  shown  in  the  cut,  meets  the  descending  shower  of 


Coal 


FIG.  40. — WEGENER'S  POWDERED  COAL  APPARATUS. 

powdered  coal,  mixes  with  it,  and  carries  it  into  the  furnace.     If 
the  air-supply  is^  sufficient,  smokeless  combustion  will  result. 

Records  of  tests  of  the  Wegener  apparatus*  indicate  that  it 
does  not  give  any  higher  economy  than  can  be  obtained  by  mechanical 
stokers,  or  other  means  of  burning  soft  coal,  which  do  not  require  the 
coal  to  be  powdered. 

*  Engineering  News,  Sept.  16,  1897. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


247 


Fig.  41  is  an  illustration  of  a  coal-dust  feeding  apparatus  built 
by  C.  0.  Bartlett  &  Snow  Co.,  Cleveland,  0.  (The  Engineer,  Chicago, 
April  1,  1904).  The  coal  dust  is  fed  from  a  storage  bin  into  the 
hopper  A,  from  which  it  is  conveyed  by  the  feed- worm  B  and  spout 
F  to  the  air  spout  D  through  which  it  is  blown  into  the  cast-iron 
spout  G  leading  to  the  furnace.  The  sueed  of  the  feed-worm  is 
adjusted  by  changing  the  position  of  the  friction  wheel  I  on  the 
plate  H.  The  air  furnished  by  the  fan  C  is  controlled  by  a  valve  E. 
A  test  of  this  apparatus  with  pulverized  coal  from  Illinois  screenings, 
40-mesh  fine,  containing  3.5  per  cent  moisture  and  17.5  per  cent  ash, 
with  a  water-tube  boiler  rated  at  280  H.P.  developed  254  H.P.  or 
90.7  per  cent  of  rating,  and  an  equvalent  evaporation  of  9.132  Ibs. 


FIG.  41. — COAL-DUST  FEEDING  APPARATUS. 


per  Ib.  of  combustible.  Taking  the  heating  value  of  Illinois  coal  at 
14,000  B.  T.  U.  per  Ib.  of  combustible,  the  efficiency  is  63.2  per  cent. 
A  much  higher  result  than  this  can  be  obtained  with  a  Dutch-oven 
furnace  and  a  mechanical  stoker. 

The  conditions  of  successful  operation  with  dust  fuel  are  stated 
as  follows  (The  Engineer,  Jan.  1,  1903)  : 

First,  the  coal  must  be  of  uniform  size  before  perfect  combustion 
can  be  had;  second,  the  coal  should  contain  a  uniform  percentage  of 
moisture;  in  other  words,  the  same  results  are  not  obtained  when 
burning  coals  containing  different  degrees  of  moisture.  Third, 
powdered  coal  should  be  burnt  in  suspension  in  air.  If  the  fuel  is 
swept  or  pushed  into  the  furnace,  the  heavy  particles  fall  to  the  bot- 
tom and  become  solid  clinker,  which  is  very  objectionable  and  almost 
impossible  to  get  out  of  the  furnace. 


248  STEAM-BOILER  ECONOMY. 

Illustrated  descriptions  of  several  other  forms  of  apparatus  for 
burning  pulverized  coal  will  be  found  in  a  "Symposium  on  Powdered 
Fuel"  in  Journal,  A.  8.  M.  E.,  Oct.  1914. 

Method  of  Burning  Petroleum.* — The  simplest  and  best  way  of 
burning  liquid  fuel  is  by  injecting  it  in  the  form  of  spray  by  means  of 
a  jet  of  steam  into  the  furnace  and  allowing  the  right  amount  of  air 
to  mix  with  it.f  The  number  of  different  injectors  or  burners  that 
have  been  devised  for  this  purpose  is  legion. 

The  simplest  device  would  consist  of  two  tubes  fastened  together, 
as  shown  in  the  annexed  sketch,  Fig.  42.  In  this,  1  is  the  oil 
feed-pipe;  2,  a  cock  for  regulating  supply  of  oil;  3,  the  steam 
pipe;  4,  the  valve  for  regulating  supply  of  steam;  5,  a  guard 
around  pipe  preventing  overflow.  The  lower  tube  is  flattened 
out  to  a  thin,  broad  opening,  from  which  the  stream  of  air  or 
steam  issues  under  pressure.  The  upper  tube  allows  a  stream  of  oil 


FIG.  42. — PETROLEUM  BURNER. 

to  flow  from  "the  supply  tank,  this  flow  being  regulated  by  the  supply 
cock.  The  oil  is  conducted  by  the  guard,  5,  which  prevents  it  flowing 
over  the  sides  of  the  lower  steam-pipe,  and  distributes  it  in  a  thin 
sheet  over  the  rapidly  issuing  steam,  with  the  result  that  the  oil  is 
rapidly  carried  forward  in  the  form  of  a  finely  divided  spray,  which 
is  the  next  thing  to  gas,  and  ignites  almost  as  easily.  By  changing 
the  shape  of  the  issuing  jet  of  steam,  different  shapes  may  be  given 
to  the  flame.  If  we  give  the  steam-jet  a  fan-shaped  opening,  the  greater 
part  of  the  oil  will  be  delivered  at  the  sides  and  we  will  have  a  wide 
and  short  flame.  If,  on  the  contrary,  we  desire  a  long,  narrow  flame, 
we  give  the  steam-jet  a  concave  opening,  then  most  of  the  oil  is 
delivered  on  the  center  of  the  steam- jet  and  is  propelled  forward  to  a 
considerable  distance. 

Those  who  try  to  improve  the  efficiency  of  a  fuel  by  altering  the 
burner  resemble  a  man  who  seeks  to  improve  the  steaming  of  his 
boiler  by  changing  the  injector.  The  place  to  work  at  and  improve  is 
inside  the  fire-box  or  combustion-chamber.  The  oil  fuel  must  be  so 
broken  up  or  pulverized  as  to  allow  of  its  mixing  with  the  air  and 

*  Extracts  from  a  paper  by  H.  Tweddle,  in  The  Engineering  and  Mining  Jour- 
rial,  Oct.  21,  1899. 

t  Spraying  or  atomizing  either  by  the  use  of  a  jet  of  air  at  high  pressure  or 
by  mechanical  means  is  now  generally  admitted  to  be  better  than  spraying 
by  means  of  a  steam  jet. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


249 


being  instantly  consumed.  If  it  is  not  consumed  in  the  fire-box,  it 
issues  either  in  the  form  of  smoke  or  of  foul-smelling,  unburned  gases, 
and  fuel  is  wasted. 

If  we  take  a  vessel  filled  with  benzine  and  set  fire  to  it,  it  burns 
with  a  heavy  flame,  and  large  quantities  of  black  smoke  are  given  of?. 
As  no  air  can  get  to  the  interior  portion,  combustion  takes  place  on 
the  outside,  and  as  the  contained  hydrogen  has  a  greater  affinity  for 
oxygen  than  carbon  has,  it  combines  with  most  of  the  oxygen  furnished 


FIG.  43. — IMPERFECT  COMBUSTION. 
(Fire  at  the  Standard  Oil  Works,  Bayonne,  N.  J.,  July  5,  1900.) 

by  the  air,  the  carbon  is  set  free  and  is  visible  in  the  form  of  a  heavy, 
black  smoke.  (See  Fig.  43.) 

If  we  admit  air  to  the  interior  of  the  volatile  gases  which  are  be- 
ing given  off,  more  oxygen  is  supplied  and  part  of  the  carbon  burns 
and  the  smoke  diminishes,  and  if  arrangements  are  made  so  as  to  ad- 
mit sufficient  air  to  all  parts  of  the  benzine  and  its  vapor,  then  we  will 
have  complete  combustion  and  no  smoke  will  be  given  off. 

In  order  to  obtain  the  greatest  efficiency  from  fuel  oil,  it  should 
be  burned  in  a  fire-brick  combustion-chamber,  so  as  to  obtain  the  very 


250 


STEAM-BOILER  ECONOMY. 


highest  possible  temperature.  Notwithstanding  the  fact  that  a  cer- 
tain amount  of  heating  surface  is  covered  by  the  brickwork,  experi- 
ments have  shown  that  there  is  both  an  increase  in  evaporation  and  a 
saving  in  fuel  with  the  lined  fire-box. 

Imperfect  Combustion  of  Oil, — Fig.  43,  reproduced  from  a  photo- 
graph of  a  fire  at  the  refinery  of  the  Standard  Oil  Co.  at  Bayonne, 
N.  J.,  gives  an  idea  of  the  amount  of  smoke  that  may  be  made  by 
burning  oil.  The  column  of  smoke  went  up  at  an  angle  to  a  height  of 
perhaps  half  a  mile,  and  then  traveled  horizontally  over  five  miles 
before  it  was  dissipated  into  the  surrounding  atmosphere. 

Use  of  Petroleum  in  Locomotives. — Mr.  Tweddle  describes  the  use 
of  petroleum  as  fuel  for  locomotives  on  the  Oroya  Railroad,  in  Peru, 
where  he  introduced  it  in  1890.  Two  locomotives,  exactly  alike  in  all 
other  respects,  were  tested,  one  with  coal  and  the  other  with  oil. 
They  were  American  Rogers  engines,  Mogul  type,  with  47  in.  drivers ; 
cylinders  18X24  in.;., weight  of  engine  38  tons,  tender  28  tons;  five 
cars  averaging  18  tons  each.  The  grades  were  as  high  as  4.2  per  cent, 
or  1  in  27,  ,with  some  sharp  curves.  The  average  consumption  of  coal 
for  a  month  was  79.30  Ibs.  per  train  mile,  and  that  of  oil  38.55  Ibs.,  or 
less  than  half. 

The  arrangement  for  the  interior  of  the  fire-box  is  shown  in  Fig. 
44.  No  alterations  were  made  in 'the  fire-box,  while  but  few  additions 


FIG.  44. — PETROLEUM  FURNACE. 


FIG.  45. — OIL  BURNER. 


were  made  to  the  regular  ash-pan.  The  back  damper  was  completely 
closed,  a  large  front  damper  with  about  2  sq.  ft.  superficial  opening 
being  arranged  in  front.  A  plate  with  an  air-opening  20  X  14  in.  sup- 
ported the  fire-brick  at  the  back  of  the  fire-box,  which  receives  the 
vaporized  oil. 

In  Fig.  45,  the  burner  is  represented.    A  is  a  general  side  view  of 
burner;  at  g  it  is  tapped  for  a    If -in.  oil-pipe,  and  at  h  for   a  J-in. 


FURNACES.— METHODS  OF  FIRING,  ETC.  251 

steam-pipe.  In  the  sectional  view,  e  e  is  the  oil-passage,  d  d  is  the 
steam-passage ;  both  these  passages  being  3  by  f  in.  D  represents  the 
front  end  of  the  burner,  and  E  represents  the  back  end  of  the  burner. 
,  The  oil  coming  through  the  passage,  e  e,  falls  directly  on  the  steam 
shooting  through  the  narrow  slit  at  -the  end  of  the  passage,  d  d,  and  is 
completely  atomized. 

With  this  burner  the  bricks  do  not  serve  in  any  way  for  breaking 
up  the  oil,  but  merely  as  a  white-hot  retort  in  which  air  and  vaporized 
oil  are  mixed  in  the  proper  proportions. 

The  supply  of  air  is  regulated  by  the  front  damper,  the  supply  of 
oil  by  a  wheel- valve  worked  by  the  fireman's  hand  in  the  cab.  The 
steam  is  seldom  touched  except  when  an  engine  is  lying  up  for  any 
length  of  time  at  a  station.  With  the  oil  and  air  under  such  easy  con- 
trol there  is  no  difficulty  in  obtaining  perfect  combustion  without 
smoke. 

The  holes  at  the  back  of  the  burner  are  closed  with  plugs.  By 
unscrewing  these  the  burner  can  be  quickly  cleaned  without  remov- 
ing; this,  however,  is  rarely  necessar}^  the  burner,  as  a  rule,  keeping 
perfectly  clean  for  an  indefinite  period. 

The  burner  is  cast  in  one  piece  and  finished  by  hand.  The  length 
of  the  burner  is  entirely  arbitrary.  The  width  is  made  to  suit  the 
quantity  of  fuel  to  be  introduced. 

On  the  heavy  grades  of  the  Oroya  line,  as  much  as  220  Ibs.  of  coal 
are  burned  per  mile,  or  110  Ibs.  of  oil.  To  perfectly  spray  such  a 
large  flow  of  oil,  a  certain  width  of  passage  is  necessary.  The  burner 
best  adapted  to  such  heavy  work  had  an  oil-passage  3  in.  wide  and  a 
steam-outlet  of  3j  in.  The  oil-aperture  was  3  by  f  in.,  the  steam- 
aperture  3J  by  1-40  in. 

Around  the  oil-opening  runs  a  sort  of  projecting  hood  which  pre- 
vents any  oil  from  leaking  when  rounding  sharp  curves.  Steam  from 
another  locomotive  is  used  in  getting  up  steam';  100  Ibs.  pressure 
from  cold  water  has  been  shown  on  the  steam-gauge  in  25  minutes, 
but  an  hour  is  generally  taken,  so  as  not  to  strain  the  boiler.  If  neces- 
sary wood  can  be  used  to  raise  steam. 

The  oil-fired  engine,  after  running  six  months,  showed  no  signs  of 
leaking  or  straining.  About  150  fire-brick  were  used  for  the  whole 
brickwork,  including  the  arch.1  This  brickwork  lasts  from  six  to 
eight  months. 

The  Hammel  Oil  Burner,  which  has  been  extensively  used  in  Cali- 
fornia is  shown  in  Fig.  46.  It  is  similar  in  principle  to  the  one 
described  by  Mr.  Tweddle. 

The  ITrquhart  Oil  Burner,  used  in  locomotives  in  Eussia,  is  shown 
in  Fig.  47.  The  oil  runs  down  a  pipe,  which  ends  in  the  external 
nozzle  of  the  injector,  while  the  steam  passes  through  the  inner  nozzle, 
which  it  enters  through  a 'ring  of  holes,  the  steam-  and  oil-cavities 


252 


STEAM-BOILER  ECONOMY. 


being  separated  by  a  stuffing-box  packed  with  asbestos.  This  pack- 
ing is  renewed  once  a  month.  The  steam-supply  is  regulated  by  a 
valve,  and  the  oil-supply  by  screwing  the  steam-nozzle  backward  and 
forward  in  the  external  nozzle,  thus  varying  the  section  of  the  annular 


A  Orifice  for  Oil  Supply  Pipe         F    Steam  Entrance 

B  Orifice  for  Steam  Supply  Pipe    G ,  H ,  I    Steam  Ducts 

C  Mixing  or  Atomizing  Chamber    J   Set  Screw  Holding  Plate 

D  Oil  Inlet  Duct  K  Removable  Steel  Plates 

E  Equalizing  Steam  Chamber         X  .Bypass  or  Blowout  Valve 

FIG.  46. — THE  HAMMEL  OIL  BURNER. 

passage.  This  is  effected  by  a  worm  and  worm-wheel,  the  latter  of 
which  is  connected  to  the  steam-nozzle  by  a  feather-key,  while  the 
former  is  on  a  shaft  which  terminates  in  a  position  conveniently  acces- 


FIG.  47. — THE  URQUHART  OIL  BURNER. 

sible  to  the  fireman.  The  injector  is  entirely  outside  of  the  fire-box, 
so  that  the  carbonizing  of  the  oil  at  the  nozzle  is  reduced  to  a  mini- 
mum. The  blast  of  oil  and  steam  is  delivered  into  the  furnace  through 
a  tube  into  which  the  nose  of  the  injector  projects,  and  through  which 
a  supply  of  air  is  also  drawn  by  the  action  of  the  jet. 

The   amount  of  steam  required   to   operate   the  injector  on  the 
Russian  railway,  according  to  Mr.  Urquhart,  is  from  $  to  13  per 


FURNACES.— METHODS  OF  FIRING,  ETC. 


253 


cent  of  the  steam  made  by  the  boiler,  the  highest  percentage  being  re- 
quired in  winter. 

A  fuel-oil  burner  using  oil  at  high  pressure  and  air  at  low  pressure, 
designed  by  H.  B.  Stilz,  Philadelphia,  is  shown  in  Fig.  48. 

This  design  comprises  an  inner  nozzle  through  which  oil  is 
forced  at  50  pounds  pressure.  Near  the  small  orifice  and  within  the 


FIG.  48. — HIGH-PRESSURE  OIL  BURNER. 

passage  is  placed  a  spindle  bearing  a  spiral  fin,  which  causes  the  oil  on 
delivery  to  rotate  and  spread  out  in  a  cone-shaped  film.  Around  the 
inner  nozzle  is  a  casing  through  which  air  passes,  and  a  spiral  fin 
gives  the  air  a  whirling  motion  as  it  passes  out. 

Mechanical  Oil  Burners.  (E.  H.  Peabody,  Proc.  Soc.  Nav.  Engrs. 
and  Marine  Archts.,  1912). — A  "mechanical  atomizer"  is  one  which 
uses  pressure  alone,  without  steam  or  compressed  air  for  spraying 
the  oil.  In  the  types  in  successful  use  the  oil  is  given  a  whirling 
motion  inside  of  the  burner  tip,  either  by  forcing  the  oil  through  a 
passage  of  helical  form,  as  in  Howden's  burner,  Fig.  49,  or  by  de- 


NOZZLE  OF 
HOWDEN  BURNER 

FIG.  49.- 


JONES  BURNER 
-MECHANICAL  OIL  BURNERS. 


livering  the  air  tangentially  to  a  circular  chamber  from  which  there 
is  a  central  outlet,  as  in  the  Jones  burner,  or  by  a  combination  of 


254 


STEAM-BOILER  ECONOMY. 


both  methods.  The  Peabody  burner,  Fig.  50,  is  of  the  tangential  type ; 
in  it  oil  is  delivered  under  pressure  to  an  annular  channel  cut  in 
the  face  of  a  nozzle  upon  which  is  screwed  a  tip  having  a  very  small 
central  chamber  communicating  with  a  discharge  orifice.  Between 


FIG.  50. — PEABODY  OIL  BURNER. 


the  nozzle  and  the  tip  a  thin  disc  is  inserted  which  has  a  hole 
in  the  center  of  the  same  diameter  as  that  of  the  central  chamber 
of  the  tip,  and  small  slots  or  ducts  extending  tangentially  from  the 
edges  of  the  central  opening  outward  to  the  annular  channel  in  the 
nozzle  so  as  to  put  it  in  communication  with  the  central  chamber. 
The  atomized  particles  of  oil  fly  off  from  the  orifice  in  straight 
lines  under  the  action  of  centrifugal  force,  thus  forming  a  hollow 
conical  spray.  A  good  burner  will  atomize  moderately  heavy  oil 
with  an  oil  pressure  as  low  as  30  Ibs.  and  from  that  up  to  200  or  above. 
If  this  range  is  insufficient  to  meet  the  variable  steam  requirements, 
it  is  better  to  shut  down  a  portion  of  the  burners  entirely  than  to 
attempt  to  adjust  each  individual  burner  separately.  The  air  supply. 
can  easily  be  controlled  for  all  burners  by  regulating  the  draft  pres- 
sure, and  the  air  can  be  closed  off  entirely  when  a  burner  is  shut 
down.  Another'  means  of  var}dng  the  quantity  of  oil  delivered  by 
all  burners  in  addition  to  alteration  of  oil-pressure  is  alteration  of 
oil  temperature.  Generally  speaking,  under  working  conditions  any 
increase  in  temperature  of  the  oil  results  in  decreased  capacity  of  the 
burners,  the  pressure  remaining  the  same.  The  reverse  is  the  case 
at  low  temperatures,  the  critical  point  depending  on  the  relationship 
between  viscosity  and  specific  volume  of  the  oil  in  question. 

Mr.  Peabody  gives  a  chart  showing  the  capacity  of  a  round  flame 
burner  with  Texas  crude  oil  of  18°  Baume,  under  200  Ibs.  pressure, 
at  different  temperatures,  from  which  the  following  figures  are  taken : 

Temp.,  deg.  F. .  .     80      90     100     110     120     130     140     160     200    240 
Lbs.  oil  per  hr. . .  350     410     430     440     430     400     370     345     310     275 


FURNACES.— -METHODS  OF  FIRING,  ETC.  255 

Furnace  Used  with  Oil  Burners. — Having  an  atomizer  that 
will  produce  a  fine  spray  with  heavy  oil,  the  next  problem  is  one  of 
furnace  design.  This  is  satisfactorily  solved  with  the  Babcock  &  Wil- 
cox  marine  boiler  furnace,  the  characteristics  of  which,  as  described 
by  Mr.  Peabody,  are:  Large  volume  in  proportion  to  the  heating 
surface  of  the  boiler;  upward  slope  of  the  roof  toward  the  rear, 
resulting  in  increase  of  height  and  volume  in  the  direction  of  the 
entering  oil  spray  and  thus  providing  for  the  expansion  and  diffusion 
of  the  gases;  small  amount  of  boiler  heating  surface  exposed,  and, 
on  the  contrary,  large  exposed  surface  of  incandescent  refractory 
material,  thus  tending  to  maintain  high  furnace  temperature  and 
promote  complete  combustion  of  the  oil;  tubes  almost  parallel  with 
the  path  of  the  oil  spray  injected  into  the  furnace  from  the  front, 
thus  promoting  proper  distribution  of  the  gases  along  the  tubes  and 
preventing  local  overheating;  outlet  from  the  furnace  at  the  point 
most  remote  from  the  location  of  the  atomizers,  thus  insuring  long 
travel  of  the  gases;  and,  finally,  means  for  bringing  the  heated 
products  of  combustion  into  the  closest  possible  contact  with  the  en- 
tire heating  surface  of  the  boiler,  discharging  the  waste  gases  into 
the  uptake  at  temperatures  but  little  above  that  of  the  steam  generated. 

Experiments  with  Oil  Burning. — With  the  atomizers  and  furnace 
above  described,  much  experimenting  was  necessary  to  determine 
the  best  form  and  dimensions  of  apparatus  for  admitting  and  distrib- 
uting air.  Great  delicacy  is  required  in  introducing  the  air  for  com- 
bustion, very  slight  changes  affecting  the  results  in  unsuspected  ways, 
and  while  almost  any  method  may  result  in  smoke- 
less combustion,  maximum  economy  and  capacity 
can  only  be  secured  by  careful  and  intelligent 
design.  It  is  not  necessary  to  give  the  air  a  whirl- 
ing motion,  but,  judging  from  rather  exhaustive 
experiments,  better  gas  analyses  are  secured,  lower 
air  pressures  are  required,  and  less  refinement  of 

adjustment  is  needed  if  the  air  is  brought   into   pIG  ^ IMPELLER 

contact  with  the  air  supply  with  the  right  sort  of  PLATE. 

twist.  The  impeller  plate  shown  in  Fig.  51 
gave  the  most  satisfactory  results.  They  are  8  in.  diameter,  set  in 
cast-iron  boxes  in  the  furnace  front.  The  nozzle  of  the  burner  is 
set  about  1  in.  outside  of  the  plane  of  the  central  opening.  Results 
of  tests  of  a  marine  boiler  with  the  Peabody  burner  will  be  found  in 
the  chapter  on  Boiler  Performance. 


256 


STEAM-BOILER  ECONOMY. 


Using  Oil  and  Coal  Conjointly,  (H.  A.  Wagner,  Power,  June 
20,  1911). — The  load  on  the  Westport  station  of  the  Consolidated 
Gas,  Electric  Light  and  Power  Company  of  Baltimore  has  well 
defined  peaks  of  comparatively  short  duration,  and  these  considerations 
led  to  experiments  with  fuel  oil  for  supplementing  the  coal  fires  and 
obtaining  the  desired  increase  in  boiler  output. 

After  trying  several  settings  the  furnace  arrangement  shown  in 
Fig.  52  was  finally  adopted.  The  space  back  of  the  usual  coal  grate 


FIG.  52. — FURNACE  FOR  BURNING  COAL  AND  OIL. 


is  made  into  a  large  combustion-chamber  with  the  oil  burners  at 
the  extreme  rear  end.  This  combustion-chamber  is  separated  from  the 
boiler  tubes  above  it  by  tiling  and  from  the  coal  grate  by  a  low  bridge- 
wall.  By  this  arrangement  either  oil  or  coal  or  both  together  may  be 
used  to  fire  the  boiler.  One  of  the  four  burners  in  each  furnace  is 
used  as  a  pilot  and  for  the  equivalent  of  a  banked  coal  fire  for 
keeping  the  boiler  ready  to  steam.  Boiler  tests  with  this  arrangement 
have  shown  approximately  the  following  results  for  maximum  boiler 
output  during  seven-hour  runs : 


FURNACES— METHODS  OF  FIRING,  ETC.  257 

Coal  alone 1188  H.P. 

Oil  alone 702  H.P. 

Coal  and  oil  together 1445  H.P. 

Coal  and  oil  maximum,  one  hour 1632  H.P. 

Under  actual  operating  conditions,  however,  the  gain  by  the  use 
of  oil  is  more  marked.  It  has  been  found  that  2000  KW.  of  station 
load  can  be  carried  by  each  boiler  when  using  coal  and  oil  together, 
with  as  much  ease  and  certainty  as  1200  KW.  per  boiler  can  be 
carried  by  coal  alone.  This  shows,  under  operating  conditions,  a 
gain  in  capacity  of  66%  by  the  use  of  oil,  or  a  saving  of  40%  in 
the  cost  of  the  boiler  plant  for  a  given  capacity. 

Tests  have  shown  that  a  cold  furnace,  with  water  in  the  boiler 
at  142°  F.,  could  be  made  to  steam  at  175  Ibs.  pressure  in  25  minutes 
with  oil  fuel  as  compared  with  42  minutes  with  coal. 

The  cost  of  fuel  oil  at  Baltimore  is  43%  more  than  coal,  per 
heat  unit,  but  in  spite  of  this  difference  the  actual  cost  of  "banking" 
is  less  with  oil  than  with  coal,  for  the  reason  that  the  oil  is  burned 
efficiently  •  while  the  coal  is  necessarily  burned  very  inefficiently. 

Practical  Considerations  in  Oil-burning,* — Heating  of  the  oil  is 
an  aid  to  economical  combustion,  and  should  take  place  as  near 
the  furnace  as  possible  and  be  carried  as  high  as  safety  permits,  but 
not  so  high  as  to  cause  the  oil  to  decompose  and  carbon  to  be  de- 
posited in  the  supply  pipes.  If  preliminary  heating  is  limited  to 
the  temperature  of  the  flash  point  of  the  oil  used,  there  can  be  no 
trouble  from  these  causes. 

In  oil  burning,  the  principal  work  of  the  fireman  is  to  see  that 
the  oil  pump  is  kept  in  constant  operation,  and  that  the  burners  do 
not  become  clogged  with  small  particles  of  foreign  matter,  scale,  etc., 
especially  when  the  installation  is  new.  Strainers  of  proper  design, 
introduced  on  the  suction  line  to  the  pump  and  also  between  the 
pump  and  the  burner,  will  reduce  this  trouble  to  a  minimum.  Burn- 
ers should  be  so  installed  that  they  can  be  easily  disconnected  from 
the  piping  and  taken  from  the  furnace  for  the  removal  of  any  foreign 
substance  from  their  restricted  orifices. 

One  of  the  most  important  questions  in  the  combustion  of  liquid 
fuel  is  the  regulation  of  the  air  supply  in  such  a  way  as  to  obtain 
perfect  combustion  before  the  gases  come  in  contact  with  the  heating 
surfaces  of  the  boiler.  This  is  usually  accomplished  by  hand  regu- 
lation of  the  damper  when  considerable  variations  in  the  load  take 
place,  supplemented  by  changing  the  position  of  the  ashpit  doors, 
which  are  kept  partly  closed  until  a  slight  tendency  to  make  smoke 

*  From  a  paper  by  B.  R.  T.  Collins,  Trans.  A.  S.  M.  E.,  1911. 


258  STEAM-BOILER  ECONOMY. 

is  noticed  in  the  furnace,,  when  they  are  opened  until  this  tendency 
disappears;  or,  better,  by  using  an  Orsat  or  continuous  C02  gas 
analyzer  to  determine  the  position  of  damper  and  ashpit  doors  which 
gives  most  complete  combustion. 

The  important  features  which  should  be  embodied  in  all  burners 
are:  easy  method  of  installation,  construction  that  will  allow  quick 
inspection,  easy  removal  of  all  foreign  material  which  may  clog  the 
burner  at  any  point,  and  rapid  and  cheap  renewal  of  any  parts  which 
are  subject  to  wear. 

The  success  of  an  oil-fuel  installation  depends  not  so  much  on 
the  type  of  burner  or  atomizer  used  as  on  the  method  of  its  installa- 
tion, and  the  intelligence  with  which  it  is  operated. 

To  conform  with  the  underwriters'  requirements,  storage  tanks 
above  the  surface  of  the  ground  should  be  placed  at  least  200  ft. 
from  inflammable  property,  and  the  top  of  the  tanks  should  be  located 
below  the  level  of  the  lowest  pipe  used  in  connection  with  the  appa- 
ratus. When  the  tanks  are  located  underground  they  should  be  out- 
side the  building,  at  least  2  ft.  below  the  surface  and  30  ft.  from 
any  building,  with  the  top  of  the  tanks  below  the  lowest  pipe  in  the 
building  used  in  connection  with  the  apparatus.  In  small  and  me- 
dium-sized installations,  steel  tanks  coated  with  tar,  having  a  ca- 
pacity of  8500  to  15,000  gallons  each,  are  generally  used.  In  larger 
installations,  reinforced-concrete  tanks,  generally  rectangular  in  shape, 
are  used.  These  are  usually  made  with  a  partition  in  the  center, 
so  that  any  sediment  or  thick  material  may  be  periodically  cleaned 
out  without  interfering  with  the  continuous  supply  of  fuel.  The 
capacity  of  the  storage  tanks  may  vary  from  a  supply  sufficient  for 
two  weeks,  when  the  oil  is  near  at  hand,  and  more  may  be  obtained 
on  one  day's  notice,  to  a  supply  sufficient  for  two  or  three  months 
when  the  source  of  supply  is  at  a  considerable  distance  and  delivery 
is  in  large  quantities  at  irregular  intervals. 

Storage  tanks  should  be  fitted  with  vent  pip.es,  indicators  show- 
ing level  of  oil  in  tanks,  filling  pipes,  arrangements  for  freeing  tanks 
from  water,  suction  pipes,  return  or  overflow  pipes,  steam  pipes  for 
filling  space  in  tanks  above  oil  with  steam  in  case  of  fire,  and  suit- 
able manholes  for  cleaning-out  purposes.  A  suitable  strainer  should 
be  installed  on  the  suction  line  between  the-  storage  tanks  and  the 
oil-pressure  pumps.  The  suction  line  should  slope  so  that  it  will 
drain  all  oil  back  to  the  storage  tanks  when  the  pump  is  stopped 
and  a  vent  opened. 

Duplicate  oil-pressure  pumps  should  be  installed  with  pump  gov- 
ernors, and  all  piping  in  connection  with  these  pumps  should  be 
cross-connected  in  such  manner  that  a  change  can  be  made  from  one 
to  the  other  and  repairs  made  to  either  without  interrupting  the 
service. 

A  suitable  oil  heater  should  be  installed,  so  that  the  exhaust 
steam  from  oil  purnps  can  be  utilized  to  heat  the  oil  before  it  reaches 


FURNACES.— METHODS  OF  FIRING,  ETC. 


259 


the  burners.  A  relief  valve  should  be  installed  on  the  discharge  line 
between  the  pumps  and  the  burners  and  set  at  a  definite  maximum 
oil  pressure. 

An  oil  meter  should  also  be  installed  in  the  discharge  line  to 
check  the  storage-tank  indicator  readings.  All  oil  piping  should  be 
installed  so  that  it  can  be  drained  back  to  the  storage  tanks  by 
gravity  in  case  of  necessity. 

Provision  should  be  made  for  removing  any  condensation  from 
the  steam  lines  to  the  burners.  Automatic  regulating  devices  should 
be  installed  to  vary  the  pressure  of  both  oil  and  steam  to  the  burners 
in  accordance  with  the  demand  for  steam  on  the  boilers,  thus  keep- 
ing a  uniform  steam  pressure  with  a  variable  load,  relieving  the  fire- 
man of  constant  adjustment  of  burner  valves  and  enabling  him  to 
take  care  of  much  larger  capacity  of  boilers  than  he  otherwise  could. 

In  case  a  plant  is  operated  only  ten  hours  per  day,  no  steam  being 
required  for  the  rest  of  the  twenty-four  hours,  it  is  necessary  to  install 
a  small  auxiliary  boiler  for  the  purpose  of  providing  steam  to  atomize 
the  oil  while  firing  up  the  main  boilers. 

Methods  of  Burning  Tar,* — Any  of  the  good  methods  of  burning 
liquid  fuel  can  be  used  successfully  with  tar,  if  it  is  heated  moderately 
and  carefully  strained. 

The  source  of  supply  should  be  a  tank  of  ample  capacity,  placed, 
say,  10  or  12  feet  above  the  burner,  and  the  contents  of  the  tank 


FIG.  53. 


FIG.  54. — COMBUSTION-CHAMBER  FOB  TAR 
BURNING. 


should  be  kept  warm  by  low-pressure  steam.     The  tar  passing  into 
and  leaving  the  tank  should  be  carefully  strained. 

Any  of  the  burners  used  for  crude  oil  will  answer  for  tar.     The 
burner  shown  in  Fig.  53  works  well. 


*  From  an  article  by  C.  F.  Pritchard  in  The  Engineer  (Chicago),  April  1, 
1903. 


260  STEAM-BOILER  ECONOMY. 

Steam  is  discharged  through  a  small  hole  less  than  1-16  in. 
diameter,  drilled  near  the  top  of  the  cap  on  the  end  of  the  J-in.  pipe. 
The  overhanging  sloping  end  of  the  tar  pipe  in  connection  with  the 
jet  of  steam  produces  a  good  spray. 

In  starting  a  boiler  a  bed  of  fuel  is  necessary,  but  after  a  short 
time  the  heat  of  the  furnace  is  sufficient  to  carry  on  combustion.  It 
is  well  to  have  a  large  combustion-chamber.  The  arrangement  shown 
in  Fig.  54,  where  the  grates  are  located  at  the  level  of  the  ash-pit  floor, 
will  be  found  satisfactory.  In  this  arrangement  no  air  is  admitted 
except  through  a  6-in.  square  hole  around  the  burner,  and  a  small 
amount  admitted  through  ports  on  the  bridge  wall  as  shown.  This 
air  passes  in  at  ports  on  the  front  of  the  boiler  and  is  heated  in  ducts 
in  the  side  walls.  This  produces  a  small  additional  economy,  but 
is  not  essential  to  good  work. 

Deflecting  or  confining  arches  or  walls  erected  in  the  furnace  will 
not  last  under  the  intense  heat  produced  by  tar  burning  at  its  best. 
A  simple  loose  cob  house  of  fire-brick,  as  shown,  is  sufficient.  This 
and  the  side  walls  of  the  furnace  become  highly  heated  and  ignite  the 
spray  of  tar,  if  from  any  reason  it  is  extinguished. 

Furnaces  for  Burning  Green  Bagasse  and  other  substances  con- 
taining a  great  deal  of  water,  such  as  wet  tan-bark,*  require  very  large 
fire-brick  combustion-chambers,  in  order  to  give  plenty  of  room  and 
time  for  the  combustion  of  the  distilled  gases  before  they  are  allowed 
to  reach  the  heating  surfaces  of  the  boiler.  The  fuel  should  be 
fed  either  in  small  quantities  at  a  time  or  else  in  a  steady  stream, 
so  that  the  evaporation  of  its  moisture  may  proceed  at  a  uniform  rate 
and  chill  the  furnace  as  little  as  possible.  Fig.  55  shows  an  end  view 
of  Cook's  bagasse  burner,  placed  between  two  water-tube  boilers. 
It  will  be  observed  that  the  structure  is  larger  than  the  boiler  set- 
ting in  end  view,  and  its  length  is  also  much  greater  than  that  of 
the  boiler-setting.  It  consists  of  a  large  fire-brick  oven  with  a 
smaller  chamber  beneath.  In  the  rear  of  the  oven,  between  it 
and  the  chimney,  a  tubular  heater  is. placed,  in  which  the  air-supply 
is  heated  by  the  gases  on  the  way  from  the  boiler  to  the  chimney. 
The  fuel  is  delivered  to  the  furnace  automatically,  by  means  of  a 
conveyor. 

Fig.  56  shows  a  bagasse  furnace  designed  by  David  Moffat  Myers. 
The  fuel  is  fed  by  gravity  to  the  feed  chutes,  which  are  provided  with 

*  For  experiments  on  tan-bark  furnaces  see  page  267. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


261 


weighted  flaps.    The  furnace  is  provided  with  step  grates  which  give  a 
large  area  for  draft. 


FIG.  55. — BAGASSE  FURNACE,  END  VIEW. 


FIG.  56. — PARTIAL  PLAN,  SIDE  AND  END  ELEVATIONS  OF  THE  MYERS  FURNACE 
FOR  BURNING  BAGASSE. 

Furnaces  for  Burning  Wood,  Sawdust,  etc. — Figs.  57,  58,  and  59 
show  three  forms  of  furnace  in  common  use  for  burning  refuse  lumber, 
shavings,  and  sawdust  in  saw-mills  and  wood-working  shops.  The 


262 


STEAM-BOILER  ECONOMY. 

.  Conveyor 


FIG.  57. — FURNACE  FOR  SAWDUST  AND  SHAVINGS. 


FIG.  58. — FURNACE  FOR  LUMBER  REFUSE. 


FIG.-  59. — FURNACE  FOR  REFUSE  LUMBER  AND  SAWDUST. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


263 


first  two  are  known  as  "Dutch-oven"  furnaces.  The  essential  features 
are :  ( 1 )  very  large  combustion-chambers,,  roofed  over  with  fire-brick ; 
(2)  provision  for  firing  the  fuel  in  the  front  portion  of  the  furnace 
and  pushing  the  partly  burned  charcoal  to  the  rear  so  as  to  form  a 
deep  bed,  over  which  the  combustible  gases  from  the  freshly  fired  fuel 
must  pass  before  they  reach  the  heating  surfaces  of  the  boiler.  The 
fuel  is  generally  fed  through  holes  in  the  roof,  the  fire-door  in  front 
of  the  furnace  being  used  only  for  long  pieces. 

The  most  common  fault  of  wood-burning  furnaces  is  that  they 
are  made  too  small  for  the  boiler  to  which  they  are  attached,  so  that 


FIG.  60. — STEP-GRATE  FURNACE. 


FIG.  61. — BLANDIN  FURNACE. 


the  full  capacity  of  the  boiler  is  not  developed.  In  some  cases  the 
trouble  may  be  remedied  by  lowering  the  grate  bars,  thus  increasing 
the  size  of  the  combustion-chamber  and  by  blowing  air  down  on  and 
into  the  burning  fuel  in  addition  to  supplying  it  through  the  grate 
bars.  Shavings  and  sawdust  may  be  more  easily  burned  by  forcing 
hot  air  against  the  pile  than  by  trying  to  get  air  through  the  pile 
from  the  grate  bars. 

The  furnace  shown  in  Fig.  59  is  said  by  J.  A.  Johnston,  in  Power, 
June  30,  1908,  to  have  proven  very  satisfactory  in  burning  sawdust 
with  a  small  mixture  of  shavings.  The  grate  must  be  kept  covered 
all  the  time,  or  too  much  air  will  get  through.  The  fuel  is  fed  in  a 
constant  stream  from  a  chute  and  is  shoved  back  over  the  grate  by 
a  man  on  the  firing  floor.  Some  labor  might  be  saved  if  the  grates 
were  inclined  instead  of  horizontal. 


264 


STEAM-BOILER  ECONOMY. 


The  step-grate  furnace,  Fig.  60,  seems  to  have  too  small  a  grate 
area  and  too  small  volume  of  combustion  space  for  the  large  heating 
surface  of  the  boiler,  and  the  Blandin  furnace,  Fig.  61,  is  also  defi- 
cient in  these  respects.  The  hanging  wall  in  Fig.  60  and  the  pro- 
jecting arch  in  Fig.  61  would  soon  burn  out  if  coal  were  used  in  these 
furnaces. 

Sawdust  and  dry  shavings  are  commonly  handled  by  blowers,  the 
suction  of  the  blower  being  connected  to  the  saw  frame  or  planer,  and 
the  refuse  being  blown  into  a  receptacle  over  the  boiler  room.  It  is 
then  dropped  by  chutes  directly  into  the  fire,  or  may  be  blown  directly 
in  by  the  blast  furnishing  air  for  the  fire. 

Conveyors  for  Shavings. — The  usual  method  of  conveying  shav- 
ings from  wood-working  machinery  to  furnaces  or  storage  .bins  is 
the  use  of  a  large  fan  on  the  suction  side  of  which  are  pipes  branching 
to  the  several  machines,  with  a  delivery  pipe  in  which  the  shavings, 
dust,  etc.,  are  blown  to  the  bin  or  furnace.  The  Shreveport  (La.) 
Blow  Pipe  Works  has  installed  many  such  systems,  some  of  them 
with  Sturtevant  exhaust  fans  60  in.  and  70  in.  diameter,  with  pipes 
up  to  35  in.  diameter.  At  Minden,  La.,  shavings  are  blown  1500  ft. 
through  a  26-in.  pipe. 

Furnaces  for  Burning  Wet  Tan. — Figs.  62  to  65  show  four 
varieties  of  furnaces  used  for  burning  wet  tan  bark.*  Fig.  62  is  a 


(BoilerJ 


L 


6'xl8;Boiler 

2042  sq.ft 
heating:  surface 


FIG,  62. — THE  EARLY  HOYT  FURNACE  FOR  BURNING  TAN  BARK. 

very  old  design,  known  as  the  Hoyt  furnace.  The  grate  surface  is 
24  ft.  long  by  6  ft.  wide,  and  the  tan  is  fed  through  five  holes  in  the 
roof  and  arranges  itself  into  as  many  piles  on  the  grate.  Fig.  63 
shows  a  shorter  and  wider  furnace  with  six  holes.  Fig.  64  is  a  still 
shorter  and  wider  furnace  with  four  holes  designed  for  the  hand  firing 
of  a  mixture  of  coal  and  tan.  It  is  supplied  with  shaking  or  shaking 


*  From  a  paper  by  David  Moffat   Myers  on  Tan  Bark  as  a  Boiler  Fuel,  Trans. 
A.  S.  M.  E.,  1909. 


FURNACES.— METHODS  OF  FIRING,  ETC. 


265 


and  dumping  grates.    Fig.  65  shows  what  is  known  as  a  hump-back 
grate,   which  provides   increased  grate   area  and  at  the.  same   time 


6'x  18'Boiler 
2089  sq.ft.  heating  surface 


FIG.  63. — A  TAN  FURNACE  WITH  Six  FEED  HOLES. 

The  setting  had  air  admission  in  the  bridge  wall  and  a  baffle  arch  in  the 
combustion-chamber.     Very  good  results  were  obtained. 


6'x  18'BdIter 
2089  sq.ft.  heating  surface 


FIG.  64. — A  FURNACE   WITH   SHAKING   GRATES  FOR   BURNING   A   COAL   AND 

TAN  MIXTURE. 

Air  spaces  over  fire  arch  and  in  walls  of  furnace  and  boiler  walls.     Distance 
from  grate  to  top  of  arch  inside  should  not  be  less  than  4  ft. 

diminishes  the  maximum  thickness  of  the  pile  of  fuel  on  the  grate 

and  thus  insures  a  free  air  supply.    The  stoke  holes  in  these  furnaces 

are     usually    provided    with    circular 

cast-iron  linings.     A  trouble  met  with 

in  these  types  of  furnace  is  the  rapid 

burning    away    of    the    fuel    next    to 

the    side    walls,    and    the    consequent 

large  leakage  of  air  from  the  ash-pit. 

This   trouble    is   overcome   to   a   great 

extent   by   making  the   furnace   about 

1  ft.  narrower  at  the  grate  bars,  and 

for  about   1   ft.   above  them,  than  the    FlG-    65.— CROSS    SECTION    OF 

,     -  , ,      ,  FURNACE  WITH  HUMP-BACK 

upper  part  of  the  furnace.  GRATES  AND  BEABING  BAR< 


266 


STEAM-BOILER  ECONOMY. 


The  Myers  furnace  for  tan  bark  or  sawdust  is  similar  to  the 
Myers  bagasse  furnace,  Fig.  56,  in  having  step  grates  and  firing  chutes 
above  the  upper  end  of  each  grate.  The  inside  dimensions  of  one 
of  his  furnaces  are :  length  8  ft.,  width  5  ft.,  height  from  bottom  of 
inclined  grates  to  center  of  arch,  5  ft.  4  in.  Mr.  Myers  has  obtained 
from  a  furnace  of  this  type  an  efficiency  as  high  as  71  per  cent  based 
on  the  available  heating  value  of  the  fuel. 

Furnaces  for  Burning  Sawdust. — Fig.  66  shows  a  furnace  for  burn- 
ing sawdust,  used  with  a  60  H.P.  return  tubular  boiler,  and  Fig.  67 


4  FIG.  66. — FURNACE  FOR  BURNING  SAWDUST. 

a  furnace  for  burning  either  sawdust  or  oil,  or  both,  used  with  a 
400  H.P.  water-tube  boiler.     In  the  latter  the  oil  is  fed  at  the  rear 


FIG.  67. — FURNACE  FOR  BURNING  SAWDUST  AND  OIL. 

of  the  boiler  in  a  three-panel  Hammel  oil  burner,  fitted  with  checkered 
grates  and  draft  doors  for  regulation  of  the  air  supply.  The  sawdust 
grates  have  a  total  area  of  148  sq.  ft.,  the  heating  surface  of  the 


FURNACES— METHODS  OF  FIRING,  ETC. 


267 


boiler  being  4070  sq.  ft.,  a  ratio  of  1  to  27.5.  The  sawdust  fuel  is 
fed  automatically  by  two  conveyors  which  bring  it  from  a  storage 
bin. 

Volume  of  Combustion  Space  Required  to  Effect  Complete  Combus- 
tion.— Technical  Paper  63  of  the  U.  S.  Bureau  of  Mines  describes  a 
series  of  experiments  to  determine  the  relation  of  the  completeness 
of  burning  the  combustible  constituents  of  furnace  gas  to  the  volume 
of  the  chamber  in  which  they  are  burned.  A  Murphy  furnace  with  a 
projected  horizontal  grate  area  of  25  sq.  ft.  was  built  at  the  end  of 
a  fire-brick  tunnel  3  ft.  wide,  2  ft.  8  in.  high  and  36  ft.  long.  Sam- 
ples of  gas  were  taken  at  the  bridge-wall  and  at  seven  other  points 
throughout  the  length  of  the  tunnel.  The  fuel  was  Pocahontas  semi- 
bituminous,  and  the  thickness  of  the  bed  was  about  6  inches.  The 
principal  results  of  the  tests  are  shown  in  the  two  tables  below. 
They  show  that  complete  combustion  (absence  of  combustible  in 
the  gas)  was  never  obtained  until  the  gases  had  traveled  beyond  a 
point  in  the  tunnel  corresponding  to  a  total  volume  of  3.2  cu.  ft.  per 


RELATION  BETWEEN  COMBUSTIBLE  IN  FURNACE  GAS  AND  VOLUME  OF  COMBUSTION 
SPACE,    WITH    AIR    SUPPLY    VARYING 


Average  Gas 
Analysis. 

tVolume  of  Combustion  Space  per  Sq.ft.  of  Grate,  Cu.ft. 

Lbs.  Coal  per 
Sq.ft.  Grate 
per  Hr. 

C02. 

0. 

1.9 

3.2 

4.5 

6 

9 

12 

Combustible  in  Furnace  Gas,  per  cent. 

f 

8.1 

11.7 

0.8 

0.3 

0.0 

20.9 

14.1 

5.3 

1.6 

0.4 

0.1 

1 

17.2 

1.9 

4.5 

1.1 

0.1 

f 

7.4 

12,2 

0.4 

0.2 

0.0 

28.4 

13.4 

5.4 

3.3 

0.4 

0.0 

I 

16.3 

2.9 

8.4 

1.0 

0.2 

f 

12.6 

6.4 

1.6 

1.2 

0.6 

37.2 

13.9 

5.1 

7.6 

2.6 

0.0 

1 

16.6 

2.4 

2.6 

0.8 

0.0 

f 

10.4 

9.0 

1.8 

0.2 

0.0 

44.3 

13.0 

6.2 

3.1 

0.2 

0.0 

1 

16.7 

0.3 

9.6 

5.5 

4.0 

3.2 

2.5 

2.4 

f 

10.4 

9.4 

2.2 

0.2 

0.0 

58.4 

15.9 

2.8 

6.8 

2.4 

1.0 

0.3 

0.2 

0.2 

17.2 

1.4 

7.5 

3.4 

1.8 

1.0 

0.6 

0.4 

268 


STEAM-BOILER  ECONOMY. 


RELATION  BETWEEN  COMBUSTIBLE  IN  FURNACE   GAS  AND  VOLUME  OF  COMBUSTION 
SPACE,    FOR    AIR    SUPPLY    CONSTANT    AT    25    PER    CENT    EXCESS 


Lbs.  Coal  per 
Sq.ft.  Grate 
per  Hr. 

Volume  of  Combustion  Space  per  Sq.ft.  of  Grate,  cu.ft. 

2 

3 

4 

5 

6 

Combustible  in  Furnace  Gas,  per  cent. 

20.9 

28.4 
44.3 
58.4 

1.2 

3.8 
3.2 
5.0 

0.0 
0.4 
0.4 
1.7 

0.0 
0.0 
0.8 

0.4 

0.0 

sq.  ft.  of  grate  area;  that  the  volume  of  combustion  space  required 
increases  with  increase  of  the  rate  of  driving  and  with  decrease  of 
the  air  supply.  Many  large  variations  from  the  average  figures 
were  obtained  on  account  of  the  inadequate  control  of  the  air  supply 
and  the  difficulty  of  obtaining  correct  average  samples  of  the  gas. 
The  figures  should  be  taken  as  applicable  only  to  the  conditions  of 
these  particular  tests.  The  general  tendency  of  the  results  is  what 
should  be  expected,  since  with  imperfect  mixing  of  the  gas  and  air 
in  the  furnace  a  longer  travel  in  the  tunnel  would  be  required  to 
effect  a  thorough  mixture  and  complete  combustion  the  smaller  the 
percentage  of  free  oxygen  in  the  gases  and  the  greater  quantity  of 
coal  burned  in  a  given  time.  In  other  words,  deficient  air  supply 
and  rapid  driving,  with  imperfect  mixture  of  gas  and  air,  are  chief 
causes  of  the  making  of  smoke. 


CHAPTER  VIII. 

SOME   ELEMENTARY   PRINCIPLES  OF  STEAM-BOILER  ECONOMY 
AND   CAPACITY— THE   PLAIN   CYLINDER   BOILER. 

IN  this  chapter  we  will  discuss  by  a  somewhat  elementary  method, 
without  the  use  of  any  algebraic  formula,  the  principles  upon  which 
depend  the  economy  and  the  capacity  of  the  heating  surface  of  a  steam- 
boiler,  using  for  illustration  the  plain  cylinder  boiler.  In  the  suc- 
ceeding chapter  the  same  subject  will  be  treated  in  another  manner, 
with  the  use  of  some  mathematics.  The  conditions  which  determine 
to  a  great  extent  how  large  a  boiler,  or  battery  of  boilers,  should  be 
used  for  a  given  purpose  are:  The  quantity  of  steam  required;  the 
quality  and  the  cost  of  fuel ;  the  degree  of  fuel  economy  desired ;  the 
quality  of  the  water  supplied ;  the  regularity  of  the  demand  for  steam ; 
the  size  and  shape  of  the  space  available,  etc. 

Let  us  consider  how  the  size  and  form  of  a  boiler  are  governed  by 
the  conditions  of  quantity  of  steam  required  and  by  the  degree  of  fuel 
economy  desired. 

Instead  of  taking  the  problem  that  is  usually  presented,  viz. :  "A 
certain  quantity  of  steam  is  required,  what  shall  be  the  form  and  size 
of  the  boiler  to  furnish  it?"  it  will  better  serve  the  purpose  of  ele- 
mentary instruction  to  state  the  problem  in  the  reverse  manner,  viz. : 
"Given  the  form  and  size  of  a  certain  boiler,  how  much  steam  will  it 
furnish?" 

Capacity  of  a  Plain  Cylinder  Boiler. — We  will  begin  the  study  of 
this  problem  by  taking  an  example  of  the  simplest  form  of  boiler,  a 
plain  cylinder  of  a  size  that  is  still  commonly  used  at  anthracite  coal- 
mines, viz. :  30  in.  diameter  and  30  ft.  long.  It  is  provided  with  a 
setting  of  brick-work,  the  side  walls  being  3  feet  apart,  and  with  an 
ordinary  grate,  3  ft.  wide  and  4  ft.  long,  or  12  sq.  ft.  of  grate-surface. 
At  the  rear  end  there  is  a  flue  leading  tvo  a  tall  chimney.  The  side 
walls  of  the  setting  are  built  in  at  the  top  so  as  to  touch  the  boiler  at 
the  middle  of  its  height,  so  that  only  one-half  of  the  boiler  is  exposed 
to  radiation  from  the  fire  and  to  contact  with  the  heated  gases.  The 
water-level  is  carried  a  few  inches  above  the  middle  of  the  boiler,  so 

269 


270 


STEAM-BOILER  ECONOMY. 


that  at  no  time  is  any  part  of  the  external  surface  of  the  boiler  ex- 
posed to  the  flame  or  heated  gases  without  having  water  on  the  oppo- 
site inner  surface.  The  boiler  is  made  of  steel,  J  inch  thick,  which  is 
ample  for  strength,  and  is  supposed  to  be  kept  free  from  scale  on  the 
inside  and  from  deposits  of  soot  and  ashes  on  the  outside.  The  up- 
per half  of  the  boiler,  above  the  brick  walls,  is  covered  with  a  non- 
conducting covering,  to  prevent  excessive  loss  of  heat  by  radiation. 
Such  a  boiler  is  shown  in  Fig.  68. 

The  boiler  being  30  ft.  long  and  2  \  ft.  external  diameter,  and  the 
lower  half  of  its  surface  being  heating  surface,  the  area  of  the  heating 
surface  is  \  of  30  X  2J  X  3.1416  =  117.81  sq.  ft.  We  can  make  this 
120  ft.  by  letting  the  side  walls  touch  the  heating  surface  \  in.  above 
the  middle  of  the  boiler;  or,  if  we  let  them  extend  7J  in.  above  the 
middle,  raising  the  water-level  to  correspond,  until  it  is  within  5  or  6 


FIG.  68. — PLAIN  CYLINDER  BOILER. 


in.  of  the  top  of  the  boiler,  we  can  make  the  heating  surface  -equal  to 
two-thirds  of  the  whole  external  cylindrical  surface  of  the  boiler,  or 
157  sq.  ft.  This  will,  however,  not  be  generally  advisable,  since  by 
bringing  the  water-level  so  close  to  the  top  of  the  boiler  there  would 
be  danger  of  carrying  water  into  the  steam-pipe,  making  what  is 
known  as  "wet  steam."  For  the  purpose  of  this  calculation,  there- 
fore, we  will  consider  the  heating  surface  as  120  sq.  ft.  The  grate- 
surface  being,  as  already  stated,  12  sq.  ft.,  the  ratio  of  heating  to 
grate-surface,  which  ratio  is  a  term  commonly  used  in  describing 
steam-boiler  proportions,  is  10  to  1. 

This  simple  form  of  boiler,  when  properly  built  and  erected,  sup- 
plied with  good  water,  and  well  taken  care  of,  has  many  excellent  quali- 
ties, which  have  caused  it  to  remain  a  favorite  form  -of  boiler  in  some 
parts  of  the  world,  and  especially  in  the  anthracite  coal  regions  of 
Pennsylvania,  ever  since  high-pressure  steam  began  to  be  used  in  steam- 
engines,  a  century  ago.  Its  disadvantages,  which  have  caused  it  to  be 
generally  displaced  by  other  forms,  will  be  treated  of  later.  The 
study  of  the  chief  conditions  which  govern  boiler-capacity  and  boiler- 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.  271 

economy  can  be  more  easily  begun  by  reference  to  this  form  of  boiler 
than  to  any  other,  and  it  is  for  this  reason  that  it  has  been  selected  for 
discussion  in  this  place.  The  theoretical  principles  which  may  be 
developed  in  treating  of  this  boiler  will  apply  in  great  measure  to  all 
other  forms  of  boilers. 

Having  thus  described  the  boiler,  we  are  now  ready  to  take  up  the 
question,  "How  much  steam  will  it  furnish?"  A  direct  answer  to 
the  question  is :  "That  depends  on  circumstances,  and  especially  upon 
the  amount  and  upon  the  quality  of  coal  that  is  burned  under  it. 
One  boiler  of  the  form  and  dimensions  here  given  may  furnish  three 
or  four  times  as  much  steam  as  another  boiler  exactly  like  it."  This 
answer  is  correct,  but  it  is  not  sufficiently  definite  for  our  purpose. 
If  the  capacity  of  the  boiler  depends  upon  circumstances,  we  wish  to 
know,  with  some  approach  to  accuracy,  what  the  boiler  will  do  under 
different  sets  of  stated  conditions,  and  how  the  conditions  affect  the 
capacity  of  the  boiler  and  at  the  same  time  the  economy  of  fuel. 

We  will  begin  this  study  by  assuming  that  under  all  the  different 
conditions  now  to  be  considered  the  steam-pressure  is  maintained  at 
110  Ibs.,  not  by  means  of  a  damper  regulator,  which  is  occasionally 
used,  but  by  the  discharge  of  the  steam  into  a  steam-main  fed  also  by 
other  boilers  in  which  main  the  steam-pressure  is  maintained  constant 
under  a  possible  varying  demand  by  means  of  varying  the  rate  of 
driving  of  the  other  boilers  than  the  one  being  considered.  The  uni- 
formity of  pressure  might  also  be  obtained  by  having  the  steam  escape 
through  a  loaded  valve,  similar  to  a  safety-valve,  which  is  set  so  as  to 
open  whenever  the  pressure  is  110  Ibs.,  and  shut  below  that  pressure. 
We  will  also  assume  that  the  feed-water  is  supplied  at  a  tempera- 
ture of  155°  Fahrenheit.  These  two  assumptions  are  made  merely 
for  the  purpose  of  simplifying  the  problem,  and  thereby  shortening  to 
some  extent  the  arithmetical  computations  involved.  To  evaporate  a 
pound  of  water  supplied  at  155°  F.  into  steam  at  110  Ibs.,  gauge- 
pressure,  requires  just  10  per  cent  more  heat  than  to  evaporate  a 
pound  of  water  supplied  at  212°  F.,  into  steam  at  ordinary  atmos- 
pheric pressure  at  the  sea-level,  or  "from  and  at  212 °,"  a  term  fre- 
quently used  in  discussions  of  boiler-economy.  Results  of  boiler-tests 
are  commonly  reduced  from  the  figures  obtained  under  the  "actual 
conditions"  of  the  test  to  the  equivalent  evaporation  "from  and  at 
212°"  by  multiplying  these  figures  by  a  "factor  of  evaporation," 
which  factor  riiay  be  found  by  calculation  from  the  formula  F  — 
(H  —  h)-+-  970.4,  in  which  H  and  h  are  respectively  the  heat-units  in 


272  STEAM-BOILER  ECONOMY. 

1  Ib.  of  steam  of  the  given  pressure  and  in  1  Ib.  of  water  of  the  given 
temperature  found  in  the  tables  of  the  properties  of  steam  and  water, 
or  it  may  be  taken  directly  from  a  table  of  such  factors.  In  the 
present  case  the  "actual  conditions"  assumed  are:  Feed- water  155°; 
steam-pressure  110  Ibs.  by  gauge  (corresponding  to  a  temperature  of 
344°  F.),  and  factor  of  evaporation  1.10. 

Calculations  of  Fuel  Economy. — We  now  assume,  as  the  first  condi- 
tion which  governs  the  rate  of  driving  of  the  boiler,  that  the  coal  used 
is  of  a  fairly  good  quality,  equal  in  heating  value  to  an  ideal  perfectly 
dry  coal  containing  85  per  cent  of  pure  carbon  and  15  per  cent  ash. 

Let  us  also  assume  that  we  have  the  draft  of  the  boiler,  and  the 
thickness  of  the  bed  of  coal  on  the  grate,  so  regulated  that  enough  air 
is  supplied  to  burn  the  carbon  of  the  fuel  thoroughly,  forming  car- 
bonic acid  gas,  or  C02.  Each  pound  of  coal  burned  will  require 
about  20  Ibs.  of  air  to  burn  it,  including  enough  excess  of  air  to  insure 
that  no  portion  of  the  carbon  is  burned  imperfectly,  or  to  carbonic  ox- 
ide gas  (CO).  The  20  Ibs.  of  air  supplied  per  pound  of  coal  will 
measure  about  260  cubic  feet,  if  measured  at  a  temperature  of  60°  F. 

The  complete  combustion  of  a  pound  of  coal  will  generate  a  defi- 
nite quantity  of  heat,  which  may  be  calculated  and  expressed  in  "heat- 
units,"  or  "British  thermal  units." 

The  quantity  of  heat  which  may  be  produced  by  the  complete  com- 
bustion of  1  Ib.  of  carbon  is,  approximately,  14,600  B.T.U. 

The  quantity  of  heat  required  to  evaporate  1  Ib.  of  water  from  a 
temperature  of  212°  into  steam  at  the  same  temperature,  or  from  and 
at  212°,  is  970.4  B.T.U. 

The  quantity  of  heat  required  to  evaporate  1  Ib.  of  water  supplied 
at  155°  into  steam  at  110  Ibs.  gauge-pressure,  is  10  per  cent  greater 
than  this,  or  1067  B.T.U. 

Dividing  14,600  by  970.4  we  obtain  15.05  Ibs.,  which  is  the  quan- 
tity of  water  which  may  be  evaporated  and  at  212°  by  the  com- 
plete combustion  of  1  Ib.  of  carbon,  on  the  supposition  that  all  the 
heat  generated  is  used  to  evaporate  the  water  and  none  is  allowed  to 
escape  by  radiation  or  in  the  gases  produced  by  the  combustion,  con- 
ditions which  are  ideal,  and  impossible  to  realize  in  practice. 

A  coal  whose  heating  value  per  pound  is  equal  to  85  per  cent  of 
that  of  pure  carbon,  is  theoretically  capable  of  producing  85  per  cent 
of  this  result,  or  0.85  X  15.05  =  12.79  Ibs.  evaporation,  from  and  at 
212°,  per  pound  of  coal. 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.  273 

If  the  steam  is  generated  at  110  Ibs.  pressure  from  feed-water  at 
155°,  the  theoretically  possible  evaporation  is  ^  of  this,  or  12.79  -+- 
1.1  =  11.63  Ibs.  of  steam  per  pound  of  coal,  1.1  being  the  "factor 
of  evaporation." 

This  is  the  maximum  amount  of  steam  which  it  is  possible,  theo- 
retically, to  produce  from  1  Ib.  of  coal  of  the  quality  assumed,  and 
under  the  conditions  given,  viz.,  feed-water  at  155°  and  steam-pressure 
110  Ibs.,  in  an  ideal  boiler,  in  which  there  is  no  waste  of  heat  by  radi- 
ation, by  escape  in  the  chimney  gases,  and  no  waste  of  coal  by  imper- 
fect combustion,  by  falling  through  the  grate-bars  or  by  removal  in 
the  ashes.  In  practice  all  these  wastes  occur,  and  the  percentage  of 
the  ideal  result  which  may  be  obtained  in  a  test  ranges  from  80,  under 
unusually  favorable  conditions,  down  to  50  or  even  less,  when  the  con- 
ditions are  unfavorable.  If  we  take  75  per  cent  as  the  highest  figure 
which  is  likely  to  be  reached  in  every-day  practice,  with  good  coal  and 
with  a  boiler  which  is  well  designed  and  driven  at  a  moderate  rate, 
then  we  may  expect  that  the  coal  of  the  quality  given,  with  feed-water 
at  155°  and  steam  at  110  Ibs.,  will  evaporate  11.63  X  .75  =  8.72  Ibs. 
as  a  maximum;  and  if  the  boiler  is  not  properly  designed  for  the  ser- 
vice, or  is  driven  at  too  high  a  rate,  or  the  air-supply  is  excessive, 
the  evaporation  per  pound  of  coal  may  be  much  less  than  this  figure. 

Reversing  the  order  of  the  calculations  we  have: 

Actual  evaporation  per  Ib.  of  coal 8. 72  Ibs. 

Equivalent  evaporation  from  and  at  212°,  8.72  X 1 .1 ....  9 . 59   " 

Equivalent  evaporation  per  Ib.  combustible,  9.59  -f- 85 ...  11 . 28  " 

Efficiency,  11.28-M5.05 75% 

Boiler  Capacity  Depends  Upon  Economy. — The  discussion  thus  far 
has  apparently  made  a  wide  digression  from  the  problem  with  which  it 
started,  viz. :  how  much  steam  will  be  furnished  by  the  boiler  of  the 
form  and  size  selected.  The  complete  answer  to  the  problem,  how- 
ever, is  so  complicated  with  the  answer  to  the  other  question  of  how 
much  steam  may  be  generated  from  a  pound  of  coal,  that  it  seemed  ad- 
visable to  first  give  some  consideration  to  the  latter  question.  It  will  be 
seen  that  the  amount  of  steam  that  may  be  made  by  a  boiler  of  a  given 
size  depends  upon  the  amount  of  coal  which  may  be  burned  under  it, 
but  is  not  directly  proportional  to  the  amount  of  coal ;  and  the  amount 
of  steam  that  may  be  generated  by  the  combustion  of  a  pound  of  coal 
depends  upon  the  boiler  and  upon  the  rate  at  which  the  boiler  is 
driven. 


274  STEAM-BOILER  ECONOMY. 

Returning  now  to  our  cylindrical  boiler  30  ft.  long,  let  us  suppose 
that  its  length  is  divided  into  10  parts  or  sections,  of  which  the  first 
two  sections  are  directly  exposed  to  radiation  from  the  fire,  and  the 
other  eight  receive  heat  by  conduction  from  the  heated  ga&es  in  their 
passage  to  the  chimney.  It  is  evident  that  the  first  and  second  sections 
will  each  transmit  a  greater  quantity  of  heat  into  the  water  than  the 
third,  that  the  third  will  transmit  more  than  the  fourth,  and  so  on. 
The  gases  will  gradually  diminish  in  temperature  as  they,  travel  from 
the  furnace  to  the  chimney.  The  amount  of  heat  transmitted  to  the 
water  by  each  square  foot  of  heating  surface  in  a  given  time  will 
depend  upon  the  difference  between  the  temperature  of  the  heated 
gases  on  one  side  of  the  plate  and  that  of  the  water  on  the  other  side ; 
the  greater  this  difference  of  temperature  the  greater  the  heat  trans- 
mitted. Experifents  show  that  it  varies  about  as  the  square  of  that 
difference.  Thus  the  heat  transmitted  will  be  four  times  as  much  when 
the  difference  is  1000°  as  when  it  is  500°. 

Considering  then  that  our  boiler  is  divided  into  sections,  as  in  Fig. 
69,  and  that  a  fire  is  burning  on  the  grate,  concuming  a  certain 

quantity  of  coal  per  hour, 
an(j  generating  a  temperature 
which  in  the  first  two  sections 

-,      6Q  averages  2600°  F.,  the  reduc- 

tion  in  temperature    may   be 

considered   to  take  place  as  follows,  the  temperature  being  taken  at 
the  end  of  each  section : 

Section  No ...    2          3          4          5         6        7        8        9        10 

Temperature  F 2200     1630     1290     1100    970    880    820    770     730 

Reduction 570      320       190     130      90      60      50      40 

The  reduction  of  the  temperature  of  the'  consecutive  sections  is  a 
measure  of  the  quantity  of  heat  transmitted  by  each  section,  for  the 
quantity  of  heated  gas  remains  the  same,  and  the  quantity  of  heat  in 
a  given  quantity  of  gas  is  very  nearly  proportional  to  its  temperature. 

Suppose  now  we  increase  the  quantity  of  coal  burned  on  the  grate, 
so  that  a  greater  quantity  of  heated  gas  is  formed.  The  thickness  of 
the  bed  of  coal  being  increased  with  the  increase  of  draft,  so  that  the 
same  amount  of  air  is  used  per  pound  of  coal,  the  same  temperature  in 
the  furnace,  viz.,  2600°,  may  be  obtained;  but  the  temperatures  of  the 
sections  beyond  the  furnace  will  be  higher  than  before,  because  the 
quantity  of  heated  gas  and  its  velocity  of  passage  toward  the  chimney 
are  both  increased,  and  the  capacity  of  a  square  foot  of  heating  sur- 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.  275 

face  to  absorb  heat  is  not  increased  by  the  increase  in  quantity  of  the 
gas  that  passes  under  it,  although  it  may  be  increased  by  the  increase 
of  the  difference  between  the  temperature  of  the  gas  and  that  of  the 
water  in  the  boiler.  The  reduction  in  temperature  of  the  gas  in  the 
consecutive  sections  may  now  be  as  f ollbws : 

Section  No 2          3          4          5          6          7          8        9  10 

Temperature  F.\  ..  2300  1920  1670  1490  1360  1250  1160  1090  1030 
Reduction 380  250  180  130  110  90  70  60 

Comparing  these  two  statements  of  the  temperature  in  the  differ- 
ent sections,  we  note  several  things : 

1.  In  the  first  case  the  temperature  of  2600°  at  the  furnace  is  re- 
duced to  730°  at  the  chimney,  and  in  the  second  case  the  same  tem- 
perature at  the  furnace  is  reduced  only  to  1030°  at  the  chimney.    In 
the  first  case  the  temperature  at  the  chimney  indicates  a  loss  of  heat 
in  the  chimney  gases  of  730  -=-  2600  =  28  per  cent  of  the  heat  in  the 
furnace.     In  the  second  case  the  temperature  of  1030°  indicates  the 
loss  of  1030  -^-  2600  =  39.6  per  cent. 

2.  In  the  second  case  the  reduction  of  the  temperature  in  the  first 
three  sections  is  Less  than  that  of  the  corresponding  sections  in  the 
first  case.    This  does  not  mean  that  the  heat  transmitted  is  less  in  the 
second  case  than  in  the  first,  for  the  quantity  of  gas  has  been  in- 
creased and  there  is  a  greater  quantity  of  heat  transmitted  while 
the  reduction  in  temperature  is  less. 

3.  In  each  section  in  the  second  case  the  temperature  is  greater 
than  in  the  corresponding  section  in  the  first  case.     The  difference 
between  the  temperature  of  the  gas  and  the  water  is  greater,  conse- 
quently the  transmission  of  heat  is  greater,  and  the  quantity  of  steam 
made  by  the  boiler  is  greater.     The  capacity  of  the  boiler  therefore 
depends  to  a  considerable  extent  on  the  economy.     Increasing  the 
quantity  of  coal  burned  increases  the  capacity  while  it  reduces  the 
economy. 

4.  Although  in  the  second  case  a  greater  quantity  of  steam  is  made 
than  in  the  first,  it  is  not  made  with  the  same  economy  of  fuel,  for 
the   temperature  of  the   chimney  gases   is   greater,   showing   that   a 
greater  percentage  of  the  heat  generated  in  the  furnace  has  been 
wasted. 

5.  Since  the  reduction  of  temperature  in  any  section  is  less  than 
that  in  the  preceeding  section,  it  is  evident  that  in  the  first  case  an 
addition  of  a  few  sections  to  the  length  cannot  add  much  to  the 


276  STEAM-BOILER  ECONOMY. 

economy  of  fuel.  In  the  second  case,  however,  the  temperature  of  the 
chimney  gases  being. 1030°,  it  is  evident  that  an  addition  of  several 
sections  to  the  length  might  be  made  before  the  gases  would  be  re- 
duced to  730°,  the  temperature  of  the  chimney  gases  in  the  first  case. 
It  is  also  evident  that  increasing  the  heating  surface  increases  both 
the  capacity  and  the  economy. 

Loss  of  Economy  Due  to  Insufficient  Heating  Surface. — What  has 
been  said  above  shows  the  necessity  of  proportioning  the  heating  sur- 
face to  the  amount  of  coal  to  be  burned,  rather  than  to  the  extent  of 
grate-surface;  and  so  proportioning  it  as  to  give  such  an  extent  of 
heating  surface  as  will  reduce  the  temperature  of  the  chimney  gases 
to  say  within  100°  or  200°  of  the  temperature  of  the  steam,  if  economy 
of  fuel  is  desired. 

Some  readers  may  think  that  all  this  is  so  very  simple  that  there 
should  be  no  need  of  explaining  it  at  so  great  length.  It  all  amounts 
to  the  simple  statement  that  economy  of  fuel  requires  that  the  tem- 
perature of  the  escaping  gases  should  be  low,  and  that,  to  secure  this 
low  temperature,  plenty  of  heating  surface  should  be  given.  This  is 
quite  true,  but  it  is  not  at  all  appreciated  by  many  boiler  users. 
Many  of  them  never  think  of  putting  a  pyrometer  or  a  thermometer 
in  the  stacks  of  their  boilers,  to  discover  by  that  means  whether  or  not 
there  is  a  waste  of  fuel.  They  are  quite  satisfied  if  their  boilers  give 
all  the  steam  that  is  required,  and  pay  little  attention  to  the  cost  of 
producing  that  steam.  It  has  therefore  seemed  desirable  that  this 
chapter  should  contain  not  only  the  simple  statement  above  given,  but 
also  in  considerable  detail  the  reasoning  upon  which  the  statement  is 
founded.  A  mathematical  treatment  of  the  subject  will  be  found  in 
the  chapter  on  "Efficiency  of  Heating  Surface." 

To  come  now  to  a  more  definite  statement  of  how  great  is  the  loss 
due  to  insufficient  heating  surface,  we  must  have  recourse  to  the 
records  of  experiments  upon  boilers. 

In  a  paper  on  "Efficiency  of  Boiler  Heating  Surface,"  by  Mr. 
R.  S.  Hale,  Trans.  Am.  Soc.  M.  E.,  vol.  xviii.,  he  gave  a  diagram 
showing  the  relation  of  the  evaporation  from  and  at  212°  per  pound  of 
combustible  to  the  evaporation  from  and  at  212°  per  square  foot  of 
heating  surface  per  hour,  as  obtained  by  plotting  the  results  of  tests 
with  anthracite  coal  given  in  Mr.  Geo.  H.  Barrus's  book  on  "Boiler 
Tests."  This  diagram  is  here  reproduced,  Fig.  70.  The  small  circles 
represent  the  results  of  each  individual  test,  the  lower  curve  represents 
what  Mr.  Hale  considers  to  be  the  law  of  the  average  relation  between 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.  277 


the  efficiency  and  the  rate  of  evaporation,  and  the  upper  line,  passing 
through  five  of  the  small  circles,  is  a  line  which  is  added  to  represent 
the  law  of  the  relation  as  derived  from  maximum  results.  It  will  be 


ft 


^s 


Lte  Evaporation  per  sq.-ft.  Heatoj  Surf,  per  Hour. 

FIG.  70. 

noticed  how  very  far  below  the  maximum  are  some  of  the  individual 
results. 

Maximum  Possible  Economy.— On  another  diagram,    Fig.  71,  is 
plotted  together  with  this  curve  of  Mr.  Barrus's  maximum  results 


Lbs.  Evaporation  per  sq.  ft.    Heating  Surface  per  Hour. 

FIG.  71. — RELATION  OF  ECONOMY  TO  RATE  OF  DRIVING. 
another    curve     representing    the     maximum     results    obtained     in 
the  boiler  tests  made  at  the   Centennial  exhibition   in   1876.     The 
particular  results  through  which  the  curve  is  drawn  are  the  following : 


Name  of  Boiler. 

Lbs.  Water  Evaporated 
from  and  at  212°  per 
sq.ft.  H.S.  per  Hour. 

Lbs.  Water  Evaporated 
from  and  at  212°  per 
Ib.  Combustible. 

Firmenich 

1  932 

11  938 

Root. 

2  586 

12  094 

Smith.                               .... 

3  739 

11  985 

Galloway.  .        .        

5.413 

11  216 

Pierce  

6.698 

9  865 

278  STEAM-BOILER  ECONOMY. 

The  smooth  curve  passes  directly  through  the  first  four  of  the 
above  results  and  a  little  above  the  fifth,  joining  the  curve  of  Mr. 
Barrus's  results  at  its  right-hand  extremity. 

As  the  Centennial  tests  were  made  under  exceptionally  favorable 
conditions,  and  as  the  maximum  results  of  these  tests  have  never  been 
surpassed  in  other  competitive  tests  with  anthracite  coal  in  which 
every  precaution  was  taken  by  impartial  observers  to  secure  accuracy, 
it  is  fair  to  consider  this  curve  as  representing  the  highest  possible 
evaporation  in  any  form  of  boiler  (except  when  mechanical  stokers 
are  used)  for  the  several  rates  of  evaporation  per  square  foot  of 
heating  surface  here  given.  Taking  approximate  values  along  dif- 
ferent portions  of  the  curve  we  have  the  following : 

POUNDS  OF  WATER  EVAPORATED  FROM  AND  AT  212°. 

Per.   sq.   ft.   of  heating 

surface  per  hour 1.7    2  2.5  3       3.5    4  4.5    5  6       7     8 

Perlb.  of  combustible.  .11.9  12  12.1  12.1  12      11.85  11.7  11.5  10.8    9.8  8.5 

Efficiency,  estimated,  %.77.7  78.3  79  79  78.3  77.3  76.4  75.1  70.5  65    55 

Assuming  anthracite  to  have  a  heating  value  of  14,800  B.T.U.  per  Ib.  combustible. 

The  Centennial  tests  were  all  made  upon  other  forms  of  boiler  than 
the  plain  cylinder,  and  the  same  is  true  of  Mr.  Barrus's  tests.  There 
is  no  record  published  of  any  comprehensive  series  of  tests  upon  plain 
cylinder  boilers  from  which  we  might  draw  a  curve  expressing  the 
relation  of  the  efficiency  to  the  rate  of  evaporation,  but  we  may  make 
certain  reasonable  assumptions  concerning  them  which  may  enable 
us  to  draw  a  probable  curve. 

The  first  assumption  is  that  the  form  of  the  plain  cylindrical  boiler 
is  exceedingly  favorable  to  the  absorption  of  the  greatest  possible 
quantity  of  heat  by  every  square  foot  of  its  heating  surface.  The 
flames  and  heated  gases  travel  steadily  along  this  surface,  the  tendency 
of  heated  gases  always  to  ascend  tending  continually  to  keep  the 
hottest  portion  of  the  gas  in  contact  with  the  surface  above  it.  There 
is  no  shorter  path  by  which  the  gases  may  reach  the  chimney;  hence, 
there  is  no  tendency  to  short-circuiting  the  gases,  which  is  a  serious 
defect  in  many  other  forms  of  boiler.  The  thickness  of  the  metal  in 
the  shell,  rarely  more  than  J  inch,  is  not  so  great  as  to  cause  an  appre- 
ciably greater  resistance  to  the  passage  of  heat  through  it  than  that 
through  the  thin  tubes  of  tubular  boilers.  The  form  of  the  plain 
cylinder  boiler  seems,  therefore,  to  be  as  well  adapted  to  the  absorp- 
tion of  heat  as  that  of  any  other  boiler,  and  there  seems  to  be  every 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER. 


reason  to  believe  that,  as  far  as  the  absorption  of  heat  through  its 
shell  from  the  heated  gases  is  concerned,  it  should  be  quite  as  efficient 
as  the  best  of  the  boilers  tested  at  the  Centennial  exhibition,  and  that 
the  curve  expressing  its  maximum  results  would  follow  closely  the 
curve  of  maximum  results  of  the  Centennial  tests,  unless  there  is  some 
other  cause  not  yet  considered  which  would  prevent  it. 

Loss  of  Heat  by  Radiation. — There  is  such  a  cause,  and  that  brings 
us  to  the  second  assumption,  viz.,  that  the  radiation  loss  of  the  plain 
cylinder  boiler  is  very  much  greater  than  that  of  the  modern  types  of 
boiler  which  were  tested  at  the  Centennial  exhibition.  The  cylinder 
boiler,  30  ft.  long  and  30  in.  diameter  and  having  120  sq.  ft.  of  heat- 
ing surface,  will  have  approximately  120  sq.  ft.  in  the  upper  half  of  its 
shell  covered  with  a  non-conducting  covering,  more  or  less  imperfect, 
and  the  two  brick  side  walls  would  be  about  240  sq.  ft.  These  two 


FIG.  72. — BATTERY  OF  PLAIN  CYLINDER  BOILERS. 

side  walls,  however,  might  be  used  for  a  battery  of  three  or  four  boilers, 
as  in  Fig.  72.  A  return  tubular  boiler  of  double  the  diameter  and  half 
the  length  of  the  cylinder  boiler,  or  5  X  15  ft.,  would  have  only  about 
80  sq.  ft.  of  the  upper  portion  of  its  shell  covered  with  a  non-conductor, 
and  about  240  sq.  ft.  side  walls,  which  might  also  be  used  for  a  battery 
of  boilers.  But  the  tubular  boiler  might  have,  say,  60  4-in.  tubes  in- 
side of  it,  with  a  total  heating  surface  of  about  940  sq.  ft.,  which  are 
entirely  surrounded  by  water,  and  therefore  contribute  nothing  to  the 
loss  by  external  radiation.  The  total  heating  surface  of  the  tubular 
boiler  would  be  about  1100  sq.  ft.,  or  nine  times  as  great  as  that  of  the 
cylinder  boiler,  and  yet  would  expose  less  surface  to  external  radiation, 
so  that  the  loss  of  heat  by  radiation  from  the  cylinder  boiler  must  be 
much  greater  than  from  the  tubular  boiler.  How  much  greater  we 
have  no  means  of  knowing,  in  the  absence  of  direct  experiments.  Mr. 
Hale,  in  the  paper  before  mentioned,  in  discussing  tests  with  other 
boilers  than  plain  cylindrical,  says  that  the  radiation  in  some  of  these 
tests  could  not  have  been  over  2  per  cent  when  the  boilers  were 
driven  at  a  rate  of  evaporation  of  3  Ibs.  of  water  per  sq.  ft.  of  heating 
surface  per  hour,  and  that  "it  does  not  seem  possible  that  the  radiation 


280 


STEAM-BOILER  ECONOMY. 


could  in  modern  practice  have  gone  up  to  much  over  6  or  7  per  cent 
at  most,  and  it  is  probable  that  it  is  not  over  5  per  cent  if  it  is  as  much 
as  that."  The  "modern  practice"  referred  to  by  Mr.  Hale,  is  not 
practice  with  plain  cylinder  boilers,  which  latter  may  be  called  ancient 
practice,  since  plain  cylinder  boilers  are  now  used  in  only  a  few  local- 
ities. We  will  probably  not  be  far  from  correct  if  we  assume  that  the 
radiation  from  plain  cylinder  boilers  is  5  per  cent  greater  than  from 
the  boilers  tested  at  the  Centennial  exhibition,  when  the  calculation 
of  the  radiation  is  made  on  the  basis  of  the  rate  of  evaporation  being 
3  Ibs.  per  sq.  ft.  of  heating  surface  per  hour,  this  5  per  cent  being 
that  percentage  of  the  total  heating  value  of  the  pound  of  combustible. 
This  heating  value,  14,600  B.T.U.,  being  equal  to  an  evaporation  of 
15.05  Ibs.  of  water,  5  per  cent  of  this  is  0.75  lb.,  which  we  may  assume 
to  be  the  extra  loss  by  radiation  in  a  plain  cylinder  boiler  over  that  in 
a  modern  type  of  boiler  when  the  rate  of  evaporation  is  3  Ibs.  per  sq. 
ft.  of  heating  surface  per  hour.  When  the  rate  of  evaporation  is 
doubled  the  percentage  will  be  halved,  and  the  extra  loss  by  radiation 
will  then  be  0.38  lb.  If  the  rate  of  evaporation  is  less  than  3  Ibs.  the 
percentage  loss  will  be  greater.  Subtracting  the  extra  loss  as  cal- 
culated from  the  figures  already  given  as  taken  from  the  curve  of 
maximum  results  of  the  Centennial  tests,  we  have  the  following : 


MAXIMUM   ECONOMY   OF   PLAIN   CYLINDER   BOILERS:     POUNDS    WATER    EVAPORATED 

FROM    AND    AT    212°. 


Per  square  foot  heating  sur- 
face per  hour  

1.7 

3 

3.5 

4 

5 

6 

8 

Per  lb.  combustible,  max.  of 
other    boilers,    Centennial 
tests     

11.90 

12.05 

12.00 

11.85 

11.50 

10.85 

8.50 

Subtract  extra  radiation  loss 
for  cylinder  boilers  
Probable  max.  per  lb.  com- 
bustible, cylinder  boilers.  .  . 

1.32 
10.58 

.75 
11.30 

.64 
11.36 

.56 
11.29 

.45 
11.05 

.38 
10.47 

.28 

8.22 

The  figures  in  the  last  line  have  been  plotted  in  the  diagram,  Fig. 
71,  and  a  curve  drawn  through  them.  It  will  be  seen  that  the  maxi- 
mum economy  is  at  a  rate  of  evaporation  of  3.5  Ibs.  per  square  foot  of 
heating  surface, ,  that  below  this  rate  the  economy  is  decreased  on 
account  of  the  loss  by  radiation,  and  that  above  this  rate  the  economy 
falls,  at  first  slowly,  and  later  very  rapidly,  until  at  a  rate  of  evapora- 
tion of  8  Ibs.  per  square  foot  of  heating  surface  per  hour  the  evapora- 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.  281 

tion  is  only  8.22  Ibs.  per  Ib.  of  combustible,  as  compared  with  the 
maximum  of  11.35  Ibs.  at  a  rate  of  3.5  Ibs. 

Beyond  the  rate  of  8  Ibs.  per  square  foot,  the  direction  of  the  curve 
between  7  and  8  Ibs.  being  continued  in  a  straight  line,  as  the  shape  of 
the  curve  seems  to  indicate,  there  would  be  a  decrease  in  the  evapora- 
tion per  Ib.  of  combustible  of  about  1.3  Ibs.  for  every  increase  of  1  Ib. 
in  the  rate,  and  the  curve  would  cut  the  line  representing  0  Ibs.  evap- 
oration per  pound  combustible  at  a  rate  of  a  little  over  14  Ibs. 

Capacity  of  a  Plain  Cylinder  Boiler  at  Different  Rates  of  Driving. 
—We  now  have  the  data  from  which  to  calculate  the  probable 
amount  of  steam  that  will  be  made  by  the  plain  cylinder  boiler,  of  the 
size  selected,  at  different  rates  of  driving. 


PROBABLE  MAXIMUM  WORK  OF  A  PLAIN  CYLINDRICAL  BOILER  OF  120  SQ.  FT. 
HEATING  SURFACE  AND  12  SQ.  FT.  GRATE  SURFACE  AT  DIFFERENT  RATES  OF 
DRIVING. 


Rate  of  driving;    Ibs.  water  evaporated 

per  sq.  ft.  of  heating  surface  per  hour.  . 

1.7 

3 

3.5 

4 

5 

6 

8 

Total  water  evaporated  by  120  sq.  ft. 

heating  surface,  per  hour,  Ibs  

204 

360 

420 

480 

600 

720 

960 

Horse-power;  34.5  Ibs.  per  hour  =  l  H.P. 

5.83 

10.43 

12.17 

13.91 

17.39 

20.87 

27.83 

Pounds  water  evaporated  per  pound  com- 

bustible                   ... 

10.58 

11.30 

11.36 

11.29 

11.05 

10.47 

8.22 

Pounds  combustible  burned  per  hour  .... 

19.3 

31.9 

37.0 

42.6 

54.3 

68.8 

116.8 

Pounds  combustible  per  hour  per  sq.  ft. 

of  grate  

1.61 

2.66 

3.08 

3.55 

4.52 

5.73 

9.73 

Pounds  combustible  per  hour  per  horse- 

power    .                  . 

3.31 

3.06 

3.04 

3.06 

3.12 

3.30 

4.16 

From  the  figures  in  the  last  line  we  see  that  the  amount  of  fuel  re- 
quired for  a  given  horse-power  is  nearly  37  per  cent  greater  when  the 
rate  of  evaporation  is  8  Ibs.  than  when  it  is  3.5  Ibs. 

The  figures  in  the  above  table  which  represents  the  economy  of  fuel, 
viz.,  "Pounds  water  evaporated  per  pound  combustible,"  and  "Pounds 
combustible  per  hour  per  horse-power/'  are  what  may  be  called 
"maximum"  results,  and  they  are  the  highest  that  are  likely  to  be 
obtained  with  anthracite  coal  with  the  most  skillful  firing  and  with 
every  other  condition  most  favorable.  Unfavorable  conditions,  such 
as  poor  firing,  scale  on  the  inside  of  the  heating  surface,  dust  or  soot 
on  the  outside,  imperfect  protection  of  the  top  of  the  boiler  from  ra- 
diation, leaks  of  air  through  the  brickwork,  or  leaks  of  water  through 
the  blow-off  pipe,  may  greatly  reduce  these  figures. 


282  STEAM-BOILER  ECONOMY. 

Disadvantages  of  the  Plain  Cylinder  Boiler,— An  inspection  of 
the  figures  will  reveal  one  of  the  reasons  why  in  most  parts  of  the 
world  the  plain  cylinder  boiler  is  no  longer  used.  The  boiler  we  have 
selected  for  illustration  is  of  quite  large  size,  30  feet  long,  2J  feet 
wide,  occupies  a  considerable  area  of  ground,  and  requires  quite  a 
costly  setting ;  yet  when  driven  at  its  most  economical  rate,  it  develops 
only  12.17  H.P.,  or  when  driven  at  such  a  rate  that  its  fuel  consump- 
tion per  H.P.  is  37  per  cent  greater  than  at  its  most  economical  rate, 
it  develops  only  37.83  H.P.  It  can  be  made  to  develop  a  still  greater 
horse-power,  but  only  by  a  much  greater  waste  of  fuel.  Where  fuel 
has  no  marketable  value,  such  as  sawdust  and  waste  lumber  at  saw- 
mills, refuse  coal  at  coal-mines,  and  the  like,  the  question  of  fuel 
economy  is  of  no  importance;  but  even  in  such  cases,  in  which,  say, 
10  or  more  pounds  of  water  may  be  evaporated  per  square  foot  of  heat- 
ing surface  per  hour,  equal  to  35  H.P.  developed  by  a  boiler  of  120  sq. 
ft.  heating  surface,  it  is  probable  that  the  first  cost  of  the  plain 
cylinder  boiler,  including  setting,  is  greater  than  that  of  some  more 
modern  form  of  boiler.  Where  refuse  coal  is  used  as  fuel,  the  cost  of 
hauling  it  and  the  cost  of  removal  of  ashes  should  be  considered,  and 
it  may  be  found  that  these  costs  alone,  even  when  fuel  costs  nothing, 
justify  the  use  of  a  boiler  which  economizes  fuel. 

Suppose  a  plant  of  boilers  at  a  coal-mine  is  used  to  generate  1000 
H.P.  of  steam.  Refuse  coal  is  used,  and  the  boilers  are  driven  at  such 
a  rate  that  4  tons  of  coal  are  used  for  every  3  tons  that  would  be  used 
by  boilers  driven  at  an  economical  rate.  It  requires  four  men  to 
handle  the  coal  and  ashes,  while  only  three  men  .would  be  required 
with  the  economical  boiler-plant.  The  saving  of  one  man's  wages, 
say,  $450  per  year,  is  equal  to  5  per  cent  on  an  investment  of  $9000, 
or  10  per  cent  on  an  investment  of  $4500.  So,  if  the  economical 
boiler-plant  of  1000  H.P.  did  not  cost  over  $4000  above  that  of  an  un- 
economical boiler-plant,  its  purchase  would  be  justified  from  a  finan- 
cial standpoint  even  in  a  case  where  fuel  costs  nothing. 

Besides  the  objections  to  the  plain  cylinder  boiler  already  spoken 
of,  viz.,  great  first  cost  when  driven  at  an  economical  rate,  great  waste 
of  fuel  when  forced  much  beyond  this  rate,  and  excessive  ground  space 
occupied,  there  are  others,  some  of  which  the  plain  cylinder  boiler 
holds  in  common  with  other  styles.  The  first  of  these  objections, 
which  is  common  to  all  very  long  boilers,  is  the  difficulty  of  support- 
ing them  in  such  a  manner  that  excessive  strains  are  not  created  in 
the  sheets  and  rivets  by  the  weight  of  the  boiler  and  the  water  inside 


ELEMENTARY  PRINCIPLES— THE  PLAIN  CYLINDER  BOILER.   283 

of  it,  in  addition  to  the  strain  due  to  the  pressure  of  steam.  When  a 
long  boiler  is  suspended  from  two  points,  whether  located  at  the  ends 
or  at  some  distance  from  them,  the  stresses  due  to  weight,  which  tend 
to  rupture  the  boiler  by  bending  it,  may  be  calculated ;  but  when  sup- 
ported at  three  or  more  points  the  stresses  are  indeterminate- — one 
support  may  sustain  much  more  weight  than  the  other — and  the  strain 
on  some  portion  of  the  shell  or  riveted  seams  may  be  greater  than  a 
proper  regard  for  safety  would  admit.  These  strains  are  apt  to  be 
changed  in  amount  or  in  direction,  as  from  tension  to  compression,  or 
vice  versa,  with  the  changes  in  temperature  in  boiler  and  setting  which 
take  place  when  the  boiler  is  put  into  or  out  of  service.  Even  if  the 
maximum  strains  due  to  the  weight  of  the  boiler  may  not  of  themselves 
be  sufficient  to  endanger  the  safety  of  the  boiler  when  new,  their  con- 
tinuance during  a  period  of  years  may  make  the  iron  hard  and  brittle, 
and  hence  give  rise  to  danger;  or  the  iron  may  in  time  become  weak- 
ened by  corrosion,  and  then  the  strains  caused  by  weight  of  the  boiler 
may  become  dangerous. 

Saving  Waste  Heat  of  the  Plain  Cylinder  Boiler.— The  chief  faults 
of  the  plain  cylinder  boiler,  its  deficiency  of  heating  surface  and  high 
first  cost  compared  to  its  capacity  when  driven  at  anything  like  an 
economical  rate,  have  led,  as  already  stated,  to  its  general  abandon- 
ment wherever  the  cost  of  fuel  is  a  matter  of  importance.  In  some  old 
plants,  however,  where  cylindrical  boilers  are  already  in  use,  and 
when  they  are  still  in  good  condition  to  furnish  steam  of  the  pressure 
desired,  but  are  driven  at  such  a  rate  as  to  be  wasteful  in  fuel,  it  has 
been  found  economical,  instead  of  replacing  the  old  boilers  with  new 
ones,  to  add  to  them  an  "  economizer"  in  which  a  large  part  of  the 
waste  heat  may  be  saved. 

Use  of  a  Water-tube  Boiler  as  an  Addition  to  a  Cylinder  Boiler. — 
Sometimes  it  is  found  that  the  waste  gases  from  a  cylinder  boiler 
are  so  high  in  temperature  that  they  may  be  advantageously  utilized 
by  passing  them  into  another  boiler.  Several  of  the  modern  forms  of 
water-tube  boiler  may  thus  be  used.  An  instance  is  given  below: 

At  one  of  the  Philadelphia  &  Reading  collieries,  one  250  H.P. 
Cahall  vertical  boiler  was  placed  at  the  rear  of  twelve  plain  cylinder 
boilers  of  the  ordinary  dimensions  common  in  anthracite  colliery 
practice.  A  simultaneous  test  was  made,  in  1896,  by  J.  M.  Whitham, 
of  the  performance  of  the  cylinder  boilers  and  the  Cahall  boiler.  Mr. 
Whitham  summarized  his  results  as  follows: 

1.  The  cylinder  boilers  are  run  to  develop  from  33  to  35  H.P.  each. 


284  STEAM-BOILER  ECONOMY. 

2.  The  cylinder  boilers  by  themselves  evaporate  3.77  Ibs.  of  water 
from  and  at  212°  per  Ib.  of  dry  coal. 

3.  The  combination  of  cylinder  boilers  and  Cahall  boilers,  the  lat- 
ter using  waste  heat  only,  permits  an  evaporation  of  6.98  Ibs.  of  water 
from  and  at  212°  per  Ib.  of  dry  coal. 

4.  The  waste  gases  enter  the  Cahall  setting  at  about  1600°  F., 
and  leave  it  about  700°. 

5.  The  use  of  waste  gases  by  the  Cahall  boiler  increases  the  avail- 
able horse-power  of  the  plant  from  74  to  85  per  cent,  according  to  the 
number  of  boilers  used  for  supplying  the  waste  heat. 

6.  The  250-H.P.  Cahall  boiler  using  waste  gases  from  eight  cylin- 
der boilers  developed  207.6  boiler  H.P.,  and  when  supplied  by  twelve 
boilers,  it  developed  334  H. P.,  or  33.6%  above  its  rating. 

7.  The  fuel  used,  called  a  "rice  mixture,"  consisted  of  20%  slate 
pickings,  8%  buckwheat,  46%  rice-coal,  and  26%  dirt.     It  contains, 
as  used  at  this  colliery,  from  6.25  to  9.5  per  cent  moisture,  and  from 
32.4  to  34  per  cent  ash  and  refuse.     It  is  burned  with  a  strong  fan- 
blast. 


CHAPTEE  IX. 
EFFICIENCY  OF  THE  HEATING  SURFACE. 

ASSUMING  that  the  fuel  is  burned  completely  in  the  furnace,  gen- 
erating a  quantity  of  hot  gas,  which  contains  all  the  heat  produced 
by  the  combustion,  we  now  have  to  consider  what  proportion  of  this 
heat  is  absorbed  by  being  transmitted  through  the  metal  heating  sur- 
face of  the  boiler  into  the  water;  in  other  words,  what  is  the  effi- 
ciency of  the  heating  surface.  This  will  depend  not  only  on  the  na- 
ture, extent,  and  arrangement  of  the  heating  surface,  that  is,  on  the 
boiler  itself,  but  also  on  the  rate  at  which  it  is  driven,  and  on  other 
conditions  of  its  operation.  A  theoretical  discussion  of  the  subject 
will  first  be  given,  and  then  the  relation  of  the  theory  to  practice  will 
be  shown. 

NOTATION. 

S  =  area  of  heating  surface  in  sq.  ft. 
W  —  actual  water  evaporated,  Ibs.  per  hour,  reduced  to  equivalent 

evaporation  from  and  at  212°,  or  U.E.*  per  hour. 
W  =  the  same  when  radiation  is  so  small  that  it  may  be  neglected, 

or  W  -\-  radiation,  in  U.E.  per  hour. 
K  =  heating  value  of  the  fuel  in  B.T.U.  per  Ib.f 
KI  =  modified  value  of  K,  after  making  allowances  for  imperfect 

combustion  and  for  hydrogen  and  moisture  in  the  fuel. 
F  =  fuel  used,  Ibs.  per  hour. 
f  =  weight  of  dry  gases  per  Ib.  of  fuel. 

fi  =  modified  value  of  /,  allowance  being  made  for  moisture  in 
the  gases  and  for  the  specific  heat  of  superheated  steam. 
w  =  jF7/,  =  weight  of  dry  gases,  Ibs.  per  hour. 
c  =  specific  heat  of  gas,  considered  as  a  constant. 
t  =  excess  of  the  temperature  of  the  water  in  the  boiler  above 
the  atmospheric  temperature. 

*  U.E.  =  units  of  evaporation,  =970.4  B.T.U. 

t  The  "  fuel "  may  be  taken  either  as  coal  or  as  combustible. 

285 


286  STEAM-BOILER  ECONOMY. 

T  =  temperature  (above  atmospheric)  of  the  gas  in  contact  with 

some  given  portion  of  the  heating  surface. 
T\,  T2  =  initial  and  final  values  of  T. 

=  total  heat  supplied  to  the  gas  by  the  burning  of  the  fuel,  on 
the   supposition  that  all  of   the  heat  generated  is  first 
utilized  in  raising  the  temperature  of  the  gas  before  it 
comes  in  contact  with  the  heating  surface. 
=  heat  lost  in  the  gases  escaping  to  the  chimney. 
a  =  a  coefficient  of  resistance  to  transmission  of  heat,  and  of 
other  elements  of  inefficiency,  more  fully  explained  later. 
ai  =  the  coefficient  a  modified,  allowances  being  made  for  in- 
complete combustion  and  for  hydrogen  and  moisture  in 
the  coal. 

Ep  =  possible  evaporation,  in  U.E.  per  Ib.  of  fuel  if  all  the  heat- 
ing value  of  the  fuel  were  utilized. 
Ea  =  actual  evaporation,  in  U.E.  per  Ib.  of  fuel. 
Ea  —  same  when  radiation  is  not  taken  into  account,  or  Ea  -h  ra- 
diation, in  U.E.  per  Ib.  of  fuel. 

R   =  radiation  in  U.E.  per  sq.  ft.  of  heating  surface  per  hour. 
In  what  follows  we  shall  at  first  consider  the  radiation  so  small 
that  it  may  be  neglected. 

Efficiency  of  the  heating  surface  =  |^  =  Cw(Tl~  TZ)  =  ^^X     (I) 

Eip  CWl  i  1  i 

This  fraction  is  the  ratio  of  the  heat  absorbed  by  the  boiler  to  the 
heat  supplied  by  the  fuel.* 

q  =  rate  of  conduction  in  U.E.  per  hour  per  sq.  ft.  of  heating 
surface,   corresponding   to  any  difference   of  temperature 
T  —  t  of  the  gas  and  of  the  water. 
qdS  =  heat  transmitted  per  hour  through  any  small  portion  dS  of 

the  heating  surface. 

cwdT  =  heat  lost  by  the  gas  in  passing  over  the  portion  of  heating 
surface  dS;  qdS  =  cwdT. 

After  the  hot  gas  passes  over  the  elementary  portion  dS  of  the 
heating  surface,  losing  the  temperature  dT,  it  arrives  at  the  next  equal 

rri          nr\ 

*  Rankine  uses  a  different  expression  for  efficiency,  viz.,   ~ — -2,  or  the 

1  i—t 

ratio  of  the  heat  absorbed  to  the  heat  which  would  be  absorbed  if  the  gases 
were  cooled  down  to  the  temperature  of  the  water  in  the  boiler.  This  is  not 
as  convenient  as  the  expression  used  above,  and  it  is  not  in  harmony  with  the 
usual  definition  of  efficiency,  viz.,  energy  utilized-:- energy  supplied. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  287 

elementary  portion  with  a  diminished  temperature,  and  transmits  heat 
through  it  at  a  diminished  rate,  since  the  rate  of  conduction  q  de- 
creases in  some  ratio  with  the  decrease  of  the  difference  of  temperature 
T  — 1\  and  so  on,  transmitting  a  less  and  less  quantity  through  each 
successive  equal  portion  of  surface,  until  it  finally  leaves  the  heating 
surface  at  the  temperature  T2. 

For  the  whole  heating  surface  8,  and  the  corresponding  decrease 
of  temperature  of  the  hot  gas  from  T\  to  T2,  we  have  the  integral  of 
the  above  differential  expression: 

cw(Tl  -  T2)  - 
or 


9 

The  second  member  of  this  last  equation  may  be  integrated  when  we 

find  the  law  of  the  relation  of  q  to  T  —  t. 

Bankine  represents  these  principles  graphically  as  follows : 

Draw  AD,  Fig.  73,  to  represent  the  whole  heating  surface  Sf  and 

let  any  portion  of  that  line,  as  AX,  represent  s,  a  part  of  that  surface. 

Let  AB  =  qiy  the  rate  of  conduction  for  the 

initial  temperature  TV     In  DA  produced, 

cw(Ti  —  0     j.i  i 

take  AO  =  -  — ;   then  the  rectangle 

OABC  will  equal  the  whole  heat  of  the  hot 
gas  proceeding  from  the  furnace  per  hour, 
measured  above  the  temperature  t\  for 

AO  X  AB  =  AO  X  qi  =  cw(Tl  -  t).  FIG.  73. 

Let  XY  =  q  =  the  rate  of  conduction  corresponding  to  the  tem- 
perature of  the  gas  after  having  passed  over  the  portion  AX  of  the 
heating  surface,  and  let  BYE  be  a  curve  drawn  through  the  summits 
of  a  series  of  such  ordinates ;  then  the  area  of  any  part  of  that  curve, 
such  as  ABYX,  represents  the  heat  transferred  per  hour  through  the 
part  AX  of  the  heating  surface;  and  the  area  ABED  the  heat  trans- 
ferred through  the  whole  surface  AD;  and  when  the  curve  BYE  is  pro- 
duced indefinitely,  the  area  contained  between  it  and  its  asymptote, 
AD  produced,  approximates  indefinitely  to  that  of  the  rectangle 
OABC. 

The  definite  results  of  these  principles  depend  on  the  relation  be- 
tween q  and  T\. 


288  STEAM-BOILER  ECONOMY. 

For  small  differences  of  temperature  it  is  found  experimentally 
that  the  rate  of  transmission  of  heat  through  metal  plates  is  nearly 
proportional  to  the  difference  of  temperature  of  the  fluids  on  the  two 
sides  of  the  plate,  but  for  great  differences  of  temperature,  such  as 
those  existing  in  steam-boiler  furnaces,  the  transmission  increases  at  a 
faster  rate  than  the  difference  of  temperature,  so  that  it  is  nearly  pro- 
portional to  the  square  of  the  difference,  as  is  shown  by  Blechynden's 

(T  _  A2 
experiments,  which  will  be  described  later.   Rankine  gives  q  =  - —     — , 

in  which  a  is  a  coefficient  whose  value  may  be  determined  by  experi- 
ment, and  he  gives  its  value  as  from  160  to  200.  The  method  of 
deducing  the  value  of  a  from  data  of  experiments  on  steam-boilers  will 
be  given  later ;  and  it  will  also  be  shown  that  it  is  a  function  of  other 
things  besides  the  resistance  of  the  metal  to  the  transmission  of  heat. 
Using  this  value  of  q  we  have 


A     CTl  dT 

cw  =   aJTt   (T  -  O2' 


(3) 

«-"«>  JTZ    {-l     —  I)" 

Whence  * 

Cf  ~j 

O  1 


cwa        T2-t        Tl-t        (T2-  t}(Tl-  t)  ' 
By  combining  equations  (1)  and  (4)  we  may  obtain 
EJ        (T,  -  Q'2  4-  T,         (T.-t)2^  T 


in  which  equation   T2  has  disappeared.      (Appendix,   note  2.)     Let 

A;   acf 

(Ti-t)B 


tf&p   =  ha     +  ha  —~,    =  ha 


*  See  note  1,  appendix  to  this  chapter,  page  335. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  289 

wr 

which  is  the  equation  of  a  straight  line  if  Ea'  and  — r  are  variables.    It 

o 

shows  that  the  evaporation  per  pound  of  fuel  is  a  function  of  the  rate 
of  evaporation  per  square  foot  of  heating  surface,  and  is  affected  by 
two  coefficients,  A  and  B. 

B,  being  a  function  of  the  initial  temperature  of  the  gas  T19  de- 
pends on  the  heating  value  of  the  fuel  and  on  the  volume  of  gas,  that 
is,  on  the  air-supply.  Let  K  =  heat-units  developed  in  the  furnace 
per  Ib.  of  fuel  burned,  =  T\fc.  Then 


_  r,-t  _  yb_    _ K-tcf 

°   ~          m  v  TS-        )          •       •       •  \PJ 


' 


expressions  from  which  we  may  find  the  value  of  A  and  B  when  the 
heating  value  of  the  coal,  the  temperature  of  the  water  in  the  boiler, 
the  weight  of  gas  per  Ib.  of  fuel,  and  the  specific  heat  of  the  gas  are 
known.  The  value  of  A,  however,  depends  upon  that  of  the  experi- 
mental coefficient  a*  (See  Appendix,  note  3.) 

Values  of  the  Coefficients  B  and  A. 

K—  tcf  ac2f2 

If  in  the  equations  B  =  -  —  =—*-  and  A  =         ^       we  substitute 

K  K—  tcj 

assumed  numerical  values  as  follows:  K  =  13,000,  14,000,  and  15,000; 
t  =  250  and  300;  c  =  0.24;  /=  20,  30,  and  40;  a  =  200,  300,  and 
400,  we  obtain  values  of  B  and  A  as  follows  : 


Values  of  B  = 

K-tcf 

K 

For  t  =  250° 

250° 

250° 

300° 

300° 

300° 

/=  20 

30 

40 

20 

30 

40 

For  #  =  13,000,  B  =  .91 

.86 

.82 

.89 

.83 

.78 

=  14,000,  B=.  91 

.87 

.83 

.90 

.85 

.79 

=  15,000,  B  =.92 

.88 

.84 

.90 

.86 

.81 

*  Up  to  this  point  the  treatment  of  this  subject  is  based  partly  on  that  of 
Rankine  (" Steam-engine."  p. 262)  and  partly  on  that  of  Hale  (Trans.  A.  S.  M.  E., 
vol.  xviii.  p.  330).  What  follows  is  original  work  of  the  author. 


290  STEAM-BOILER  ECONOMY. 


For  J  =  250° 

250° 

250° 

300° 

300° 

300 

/=  20 

30 

40 

20 

30 

40 

For 

#  =  13,000, 

a  =  200, 

A  =  .39 

.92 

1 

.74 

.40 

.95 

1.82 

=  300, 

A  =  .59 

1 

.39 

2 

.61 

.60 

1 

.43 

2.73 

=400, 

A  =  .78 

1 

.85 

3.48 

.80 

1 

.91 

3.64 

For 

#  =  14,000, 

a  =  200, 

A  =  .36 

.85 

1 

.59 

.37 

.87 

1.66 

=  300, 

A  =  .54 

1 

.27 

2 

.38 

.55 

1 

.31 

2.48 

=  400, 

A  =  .72 

1 

.70 

3 

.18 

.73 

1 

.75 

3.31 

For 

#  =  15,000, 

a  =  200, 

A  =  .33 

.79 

1 

.46 

.34 

.81 

1.52 

=  300, 

A  =  .50 

1 

.18 

2 

19 

.51 

1 

21 

2.28 

=400, 

A  =  .67 

1 

.57 

2. 

93 

.68 

1 

61 

3.04 

Graphical  Interpretation  of  Formula  (7). — On  a  system  of  rectan- 
gular co-ordinates,  Fig.  74,  lay  out  Ep  and  BEP  as  ordinates  and  — 

S 
as  abscissa.     From  the  end  of  the  ordinate 

BEP  draw  a  straight  line  inclining  downwards 
at  an  angle  whose  tangent  is  A.    Then  for 

W 

^      any  value  of  the  abscissa  —  the  correspond- 

03  ' 

ing  value  of  Ed  will  be  the  length  of  the 

ordinate  drawn  from  the  extremity  of  —  to 
_,      7/  & 

the  inclined  line.    The  inclined  line  can  never 

W 

reach  the  axis  of  abscissas,  and  the  rate  of  evaporation  ——  can  never 

S 


be  as  great  as  ~~^-.     (Appendix,  note  4.) 
A. 

Kadiation  Considered. — In  the  above  formulas  no  account  has  been 
taken  of  radiation  into  the  atmosphere  from  the  external  walls  of  the 
boiler  and  furnace.  For  a  given  value  of  F  and  8  radiation  will  tend 
to  reduce  the  values  of  Ed  and  W.  Let  r  =  radiation  expressed  in 
units  of  evaporation  per  Ib.  of  fuel,  then  total  radiation  per  hour  =  rF, 

77T 

and  radiation  in  U.E.  per  hour  per  sq.  ft.  of  heating  surface  =  —  =  R. 

S 

Ea'  =  Ea  +  r.     W  =  W  +  RS. 
Formula  (7)  then  becomes 

E.-BE9-A&+R\-r.       .     .     .        (10) 

For  a  given  temperature  t  of  the  water  in  the  boiler  and  ordinary 
furnace  conditions,  rF  and  R  will  be  practically  constant.  They  will 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


291 


represent  but  a  small  percentage  of  the  heat  generated  in  the  furnace 
when  the  rate  of  driving  is  high,  and  a  large  percentage  when  the 
rate  becomes  very  low. 

If  RQ  =  radiation  expressed  as  a  ratio  (or  percentage  -f-  100)  of 
the  total  heat  generated  (or  of  the  possible  evaporation  Ep)  and  R,  r, 

W,  S,  and  Ea  are  as  already  defined,  R0  =  -^-  =  R— -— 2;  that  is,  the 


per  cent  loss  by  radiation  is  proportional  to  the  radiation  factor  R  and 
to  the  efficiency  Ea/EPJ  and  inversely  proportional  to  the  rate  of  driv- 
ing W/S. 

Graphical  Representation  of  Formula   (10), — Formula  (10)  may 

W 

be  expressed  Ea  =  BEP  —  A-^-  —  AR  —  r, 
»  o 

and  it  may  be  represented  graphically  as 
in  Fig.  75,  the  height  Ea  of  any  point  of 
the  curved  line  above  the  base  line  repre- 
senting the  actual  evaporation  correspond- 
ing to  a  certain  rate  of  evaporation  W/S. 
In  the  equation  there  are  three  quantities 
which  are  subtracted  from  BEP,  and  these 
are  shown  on  the  diagram:  A  R,  a  con- 
stant; AW/S,  which  increases  directly  as 
W/S',  and  r  =  RS/F,  which  increases 


rapidly  as  W/S  approaches  0.   When  W/S  and  Ea  =  0,  r 
Efficiency  when  Radiation  is  Considered.  — We  have 


FIG.  75. 

BEV  -  AR. 


RS      RSE 


smce 


rF         , 

--       and 


W 


Substituting  this  value  of  r  in  eq.  (10)  it  becomes 
W  RSE°         BE" 


1+w 


A 

-  A 


W 
-j. 


(See  note  5,  Appendix.) 


Ea 
Effidency  =  -  , 


B 


AW 
—  -  _. 

+  w 


(ID 


(12) 


An  Arithmetical  Example. — Consider  first  the  case  in  which  ra- 
diation is  so  small  that  it  may  be  neglected.    We  will  suppose  the  fol- 


292  STEAM-BOI-LER  ECONOMY. 

lowing  data  to  have  been  obtained  in  a  test  of  a  boiler,  and  assume 
that  all  the  fuel  is  completely  burned,  the  whole  of  the  heat  generated 
being  first  applied  to  raising  the  temperature  of  the  gases  of  combus- 
tion before  they  come  in  contact  with  the  heating  surface : 

Heating  value  of  the  fuel  =  K  =  13,570  B.T.U.  per  Ib. ; 
Ep  =  13,570  -f-  970.4  =  13.98  U.E.  per  Ib.  of  fuel, 

S  =  1000  sq.  f t. ;  F  =  300  Ibs.  per  hr.  ; 

W  =  75%  of  13.98  X  F  =  10.485  X  300  =  3145  Ibs.  per  hour; 

/  =  24  Ibs.  gas  per  Ib.  fuel;  c  =  0.24,  specific  heat; 

w  =  Ff  =  7200  Ibs.  gas  per  hour. 

TT         -jo  K>yr\ 

=  2356°  elevation  above  atmospheric  temperature; 


fc         5.76 

=  75%  efficiency;  T2  =  25%  of  2356  =  589°; 


-T2 


t  =  temperature  of  water  —  atmospheric  temperature, 

=  341°  F.  -  60°  =  281°; 
T1  -  T2  =  1767°;         Tl  -  t  =  2075°;         T2  -  t  =  308*°. 

We  now  have  all  the  values  required  for  substitution  in  formula  (4) 
except  a. 

Formula  (4)  is 

S  1  1  Tl  -  T2 


cwa       T2  -t       Tl  -t       (T2  -  0(7*1  -  0* 
Substituting  the  values,  we  have 

1000  J_          1  1767 

0.24  X  7200  X  a       308       2075       308  X  2075* 

Whence  a  =  209.3. 

Take  now  formula  (7),     Ea'  =  BEP  -  A^. 

o 


or,  from  „.  („,  B  -  ..-.  .„ 


EFFICIENCY  OF  THE  HEATING  SURFACE.  293 


2         209.3  X  0.242  X  242 
and  eq.  (9),          A  -      -       =  .      13?570  _  1619       =  0.581. 


EJ  =  BEP  -  A^-  =  0.8807  X  13.98  -  0.581  ^^  =  10.485. 

o  1UUU 


=  75%  efficiency. 

2.  We  will  now  assume  that  radiation  from  the  boiler  and  furnace 
amounts  to  2%  of  the  heating  value  of  the  fuel,  reducing  the  efficiency 
to  73%  instead  of  75. 

2%  of  EP  =  13.98  X  .02  =  0.280  =  r. 

rF_  0.280  X  300 
S  =  1000 

=  0.084  U.E.  per  hour  per  sq.  ft.  of  heating  surface. 
W  =  W  -  R8=  3145  -  84  =  3061. 

Itom.U  (11),  E.  =  -^fo-A%  =  °-88°7XS1f  98-0-58lf^ 
1  +  f  1  + 


10.  205  U.E.  per  Ib.  fuel. 


E  B          AW 

Formula  (12),  efficiency,  -^  =  -       —^ 


0.8807         0.581  X3061 

=  0.7o. 


1,_84_      1000X13.98 
f  3061 

NOTE. — If  the  fuel  contains  hydrogen  and  water,  the  values  of  B 

and  A  should  be  obtained  respectively  from   — ^ —  and         •       and 

1\  1\  —  t 

not  from  eqs.  (8)  and  (9),  since  the  value  of  K  in  these  equations, 
determined  from  the  analysis,  is  the  total  heating  value,  the  water  in 
products  of  combustion  being  condensed  and  cooled  to  the  atmospheric 
temperature.  The  theoretical  value  of  7\  may  be  obtained  by  the 
formula  given  on  page  31. 


294  STEAM-BOILER  ECONOMY. 

General  Formulas  for  Efficiency.  —  If  in  eq.  (11), 

BE,  W 

&a   =  -  «-    —  A  -7, 


we  substitute  the  values  of  B  and  A  from  eqs.  (8)  and  (9),  viz., 


we  obtain 


an  equation  in  which,  if  we  consider  c,  the  specific  heat  of  the  flue- 
gases,  as  a  constant,  =  0.24,  there  are  no  less  than  six  variables,  viz., 
K,  t,  j,  r,  W/S,  and  a.    For  a  given  fuel  and  a  given  steam-pressure 
in  the  boiler  K  and  t  may  also  be  taken  as  constants. 
Since  EP  =  K  -5-  970.4,  we  may  write 


_          K-tcf         _     ac*f*      W 
' 


970.4(1+4)      (* 
Also  the  efficiency 

#a  K-tcf  970.4      qc2/2      Tf 


Interpretation  of  Equation  (13).  —  For  a  given  fuel,  completely 
burned  in  the  furnace,  and  a  given  steam-pressure,  the  evaporation 
per  pound  of  combustible  will  depend  — 

1.  On  the  heating  value  of  the  combustible,  or  K. 

2.  On  the  elevation  of  the  temperature  of  the  water  in  the  boiler 
above  the  atmospheric  temperature,  or  t. 

3.  On  /,  the  weight  of  flue-gases  per  pound  of  combustible,  which 
depends  on  the  force  of  the  draft  and  on  the  thickness  of  the  bed  of 
fuel  and  other  obstructions  to  the  draft,  such  as  choked  air  or  gas 
passages,  clinker  on  the  grates,  etc. 

4.  On  the  rate  of  driving,  W/S,  which  depends  on  the  quantity  of 
fuel  burned  per  square  foot  of  heating  surface. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  295 

5.  On  the  loss  by  radiation,  which  may  be  reduced  to  a  small 
amount  by  diminishing  the  extent  of  radiating  surface  and  by  clothing 
it  with  non-conducting  material. 

6.  On  the  value  of  the  coefficient  a,  which  is  not  merely  a  coefficient 
of  the  resistance  to  conduction  of  heat  through  the  metal  plates  of  the 
boiler,  as  it  has  hitherto  been  considered  in  theoretical  discussions  of 
the  subject,  but  is  also  a  function  of  the  method  in  which  the  gases 
pass  over  the  heating  surface,  and  of  the  proportion  of  the  whole 
heating  surface  which  is  properly  covered  by  the  currents  of  hot  gas 
as  they  pass  from  the  furnace  to  the  chimney-flue,  not  being  "short- 
circuited"  or  covered  by  eddies  of  cool  gas.    If  a  boiler  has  its  heating 
surface  of  moderate  thickness,  clean  inside  and  out,  and  the  water  on 
one  side  has  a  circulation  sufficient  to  sweep  away  steam  or  air-bubbles 
as  fast  as  they  form  on  it,  the  value  of  the  coefficient  a  should  be  low ; 
but  if  under  these  favorable  conditions  the  gas-passages  have  such  an 
arrangement  or  such  proportions  as  to  allow  of  the  short-circuiting  of 
the  current  of  gas  or  the  formation  of  eddies  of  cool  gas,  then  the 
value  of  a  may  be  high.     It  should  be  noted  that  the  coefficient  a  as 
here  used  is  not  a  "constant  of  nature"  whose  value  is  derived  from 
direct  experiments  on  heat  transmission,  but  is  only  the  result  of  com- 
putation of  a  complex  formula  (see  eq.  16)  which  contains  six  other 
variables.    Any  error  in  the  observed  data  which  affects  the  value  of 
any  of  these  variables  will  therefore  affect  the  computed  value  of  a. 

Large  values  of  /,  R,  and  W/S  indicate  losses  of  heat  due  respec- 
tively to  excessive  supply  of  air,  to  excessive  radiation,  and  to  exces- 
sive rate  of  driving.  A  large  value  of  a  indicates  a  loss  of  heat  which 
may  be  due  to  one  or  more  of  several  causes,  such  as  excessive  thick- 
ness or  defective  conducting  power  of  the  metal,  coatings  of  scale  or 
grease  on  one  side  of  the  metal,  or  of  soot  or  dust  on  the  other,  short- 
circuiting  of  the  gases,  or  imperfect  combustion.  The  multifarious- 
ness  of  this  coefficient,  therefore,  may  cause  it  to  have  a  very  wide 
range  of  values,  say  from  100  to  600,  instead  of  the  narrow  range,  160 
to  200,  given  by  Eankine. 

The  Coefficient  a  as  a  Criterion  of  Boiler  Performance. — If  we  have 
the  following  data  obtained  from  the  test  of  a  boiler: 

K  =  heating  value  per  Ib.  of  combustible ; 
W/S  =  evaporation  per  sq.ft.  of  heating  surface  per  hour; 

t  =  temperature  of  the  steam ; 
Ea  =  evaporation  from  and  at  212°  per  Ib.  combustible, 


296  STEAM-BOILER  ECONOMY. 

we  may  form  an  approximate  estimate  of  whether  or  not  the  perform- 
ance is  high  for  the  given  rate  of  driving  by  the  following  method: 
From  formula  (14)  we  obtain 


a  = 


K-tcf  I  c*P       W 

/"*    \  -f^  Q,     I  •  s~-r-r  '         7T"          ^*    . 


. 
9701  +R 


(16) 


For  a  high  evaporation  with  given  values  of  K,  £,  and  W/S  it  is 
necessary  that  /and  R  be  low,  say/  =  20  and  R  =  0.1.  Substitut- 
ing these  values  in  the  above  equation  and  taking  c  =  0.24,  we  obtain 


a  = 


K-t.8t  23.04       W 


970(1  +  0.1 1) 


If,  on  substituting  in  this  equation  the  observed  values  of  K,  t, 
W/S,  and  Ea,  the  value  of  a  comes  between  200  and  400,  the  per- 
formance may  be  considered  high;  if  much  above  400,  it  is  from 
fair  to  low.  The  cause  of  low  performance  may  be  low  temperature 
of  furnace,  due  either  to  imperfect  combustion  or  to  excessive  air- 
supply;  short-circuiting  of  the  gases,  rendering  the  heating  surface 
ineffective;  air-leaks  into  the  setting;  moisture  in  the  coal  or  in  the 
air;  unclean  heating  surface;  or  excessive  radiation.  Examples  of 
the  use  of  this  criterion  will  be  found  in  the  chapter  on  Eesults  of 
Steam  Boiler  Trials. 

W 

Effect  on  Ea  of  Variations  of  f,  R,    —  ,  and  a.  —  We  shall  now 

*S 

make  some  computations  of  different  values  of  Ea,  or  the  evaporation 
from  and  at  212°  per  pound  of  combustible,  based  on  assumed  con- 
stant values  of  K,  t,  and  c,  and  various  values  of  /,  R,  a,  and  W/S. 
Assume  that  the  coal  is  anthracite,  with  a  heating  value  of  K  =  14,800 
B.T.U.  per  Ib.  combustible;  that  £  =  300°,  corresponding  to  steam 
of  140  Ibs.  gauge  pressure,  and  atmospheric  temperature  of  60°;  and 
c,  the  specific  heat  of  the  flue-gases,  =  0.24.  Then  tc  =  72  ; 


EP  =  14,800  -5-  970.4  =  15.251; 
14,800-72/ 


W 


14,800  -?2 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


297 


Now  assume  that  /  =  20  and  a  =  200,  and  with  four  different 
values  of  E,  viz.,  0,  0.05,  0.1,  and  0.2,  calculate  the  effect  of  radiation 
upon  the  values  of  the  actual  evaporation  per  Ib.  combustible,  Ea,  and 
the  efficiency,  Ea  -5-  Ep,  for  different  rates  of  driving,  W+  S.  The 
results  are  as  below  : 

Values  of  Ea  and  Ea/EP  with  K 

W/S=  I 

#  =  0,       Ea        =lbs.  13.422 

Ea/Ep  =  %    88.01 
#=0.05,  #a        =lbs.  12.767 

"       Ea/Ep  =  %    83.71 
#=0.1,    Ea        =lbs.  12.171 

Ea/Ep  =  %    79.80 

#  =  0.2,    Ea        =lbs.  11.128 

«       Ea/Ep  =  %    72.97 

To  determine  the  effect  of  various  values  of  /,  or  the  weight  of 
dry  chimney-gas.es  per  pound  of  combustible,  upon  the  evaporation 
and  efficiency,  take  R  =  0.1,  a  =  200,  and  /  =  20,  25,  30,  and  35. 
The  computation  gives  the  results  below: 


ith  K  =  14,800,  t  =  300,  /  =  20, 

a  =  200. 

2 

3 

4 

6 

8 

13.077 

12.732 

12.387 

11.698 

11.008 

85.74 

83.48 

81.22 

76.70 

72.18 

12.742 

12.507 

12.217 

11.583 

10.923 

83.55 

82.01 

80.11 

75.95 

71.62 

12.422 

12.292 

12.052 

11.473 

10.838 

81.45 

80.60 

79.02 

75.23 

71.06 

11.823 

11.872 

11.732 

11.258 

10.673 

77.54 

77.84 

76.93 

73.82 

69.98 

w/s 

/=20, 

(  i 

/  =  25, 

1 1 

/=30, 

<  i 

/=35, 


Values  of  Ea  and  Ea/Ep  with  K  =  14,800,  t  =  300,  R  =0.1, 


Ea        =lbs.  12.171 
Ea/Ep  =  %    79.80 
Ea        =lbs.  11.625 
Ea/Ep  =  %    76.22 
Ea        =lbs.  11.021 
Ea/Ep  =  %    72.26 
Ea        =lbs.  10.356 
Ea/Ep  =  %    67.90 


=  200,  /=  20  to  35. 

2 

3 

4 

6 

8 

12.422 

12.292 

12.052 

11.473 

10.838 

81.45 

80.60 

79.02 

75.23 

71.06 

11.651 

11.302 

10.855 

9.854 

8.800 

76.39 

74.11 

71.11 

64.61 

57.70 

10.765 

10.145 

9.428 

7.891 

6.303 

70.59 

66.52 

61.82 

51.74 

41.33 

9.754 

8.799 

7.751 

5.553 

3.306 

63.96 

57.69 

50.82 

36.41 

21.68 

In  like  manner,  we  obtain  the  effect  of  variations  in  the  value  of 
the  coefficient  a  as  follows : 

Values  ofEa  and  Ea/Ep  with  K  =  14,800,  *  =  300,  #=0.1, 


/= 20,  a  =  100  to  400. 


W/S=  1 

a  =  100,  Ea        =lbs.  12.344 
"       Ea/Ep  =  %    80.94 
a  =  200,  #a        =lbs.  12.171 
11       Ea/Ep  =  %    79.80 
a =300,  #a        =lbs.  12.000 
Ea/Ep  =  %    78.68 


2 

3 

4 

6 

8 

12.767 

12.810 

12.742 

12.507 

12.217 

83.71 

83.99 

83.58 

82.01 

80.11 

12.422 

12.292 

12.052 

11.473 

10.835 

81.45 

80.60 

79.02 

75.23 

71.06 

12.077 

11.775 

11.362 

10.438 

9.458 

79.19 

77.21 

74.50 

68.44 

62.02 

a  =  400,  Ea 


:lbs.  11.826        11.732        11.258 


Ea/EP  =  %    77.54         7693 


73.82 


10.673 
69.98 


9.403 
61.65 


8.078 
52.97 


298 


STEAM-BOILER  ECONOMY. 


The  values  of  the  efficiency  Ea/Ep  given  in  the  tables  are  plotted 
in  the  diagrams  on  the  following  pages. 

The  Effect  of  Variation  in  the  Steam-pressure,  giving  different 
values  of  t,  the  elevation  of  the  temperature  of  the  steam  above  that 
of  the  atmosphere,  is  shown  below : 


Values  of  Ea  and  Ea/Ep  with  K  =  14,800,  /  =  20,  #=0.1,  a  =  200,  and  J  =  150°, 
250°,  and  300°,  corresponding  respectively  to  steam-gauge  pressures  of  0,  65, 
and  142  Ibs.,  and  atmospheric  temperature  of  62°  F. 

W/S=  1 

«  =  150°,  Ea        =lbs.  12.863 

Ea/Ep  =  %  84.34 

*  =  250°,  Ea        =lbs.  12.402 

Ea/Ep  =  %     81.32 

*  =  300°,  #«        =lbs.  12.171 

Ea/Ep  =  %    79.80 


2 

3 

4 

6 

8 

13.164 

13.059 

12.847 

12.308 

11.712 

86.32 

85.63 

84.24 

80.70 

76.79 

12.669 

12.547 

12.318 

11.752 

11.132 

83.01 

82.27 

80.77 

77.06 

72.99 

12.422 

12.292 

12.052 

11.473 

10.838 

81.45 

80.60 

79.02 

75.23 

71.06 

FIG.  76. — EFFECT  OF  STEAM-PRESSURE  UPON  EFFICIENCY. 


Effect  of  Heating  Value  of  Fuel  on  Efficiency. — The  value  of  K, 
or  B.T.U.  per  Ib.  combustible,  may  vary  from  about  20,000  for  petro- 
leum to  about  6000  for  wood.  The  formula  (13)  will  not  apply  with- 
out modification  to  either  of  these  fuels,  since  another  term  would  have 
to  be  subtracted,  representing  the  heat  lost  in  the  superheated  steam 
in  the  chimney-gases,  derived  from  the  combustion  of  the  hydrogen 
in  both  fuels  and  from  the  moisture  in  the  wood.  Neglecting  this 
subtractive  term  and  taking  two  hydrogenous  coals,  one  with  a  heating 
value  of  16,000  B.T.U.  per  Ib.  combustible,  about  the  highest  figure 
for  semi-bituminous  coal,  and  the  other  with  13,600  B.T.U.,  corres- 
ponding to  a  highly  volatile  Illinois  coal,  assuming  /  =  20,  a  =  200, 
c  =  0.24,  t  =  300,  and  substituting  these  values  in  equation  (13),  we 
obtain  the  following: 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


299 


£  52 
.^  50 

£« 

46 
<M 

42 
40 
38 
36 
34 
3E 
30 
28 
£6 
Z4 
22 
20 


r/77^/7  C/7 


5  77/Y/7 


Gzlloway. 


\  E  3  4-  5  6  7  8 

Lbs.  Water  Evaporated  from  and  at  2I2°F.  per  sq.-ft.  of  Heatina, Surface perHour. 

FIG.  77. — CURVES    OF    CALCULATED    EFFICIENCIES    FOR   DIFFERENT    RATES 

OF  DRIVING,  for  K=  14,800,  R  =  0.1,  t  =  300  (except  one  curve,  t  =  250) 

/=  20  to  35,  a  =  100  to  400. 


70 


=     I  23  567 

FIG.  78.— EFFECT  OF  RADIATION  UPON  EFFICIENCY. 


300 


STEAM-BOILER  ECONOMY. 


2 

3 

4 

6 

8 

11.176 

10.989 

10.709 

10.051 

9.344 

79.74 

78.41 

76.34 

71.72 

66.67 

12.422 

12.292 

12.052 

11.473 

10.838 

81.45 

80.60 

79.02 

75.23 

71.06 

13.656 

13.576 

13.372 

12.859 

12.287 

82.82 

82.34 

81.10 

78.00 

74.52 

Values  of  Ea  and  Ea/Ep  corresponding  to  #  =  13,600,  14,800,  and  16,000,  no 
allowance  being  made  for  heat  lost  in  superheated  steam  in  the  chimney-gases. 

W/S=  1 

#  =  13,600,  Ea       =lbs.  11.013 

Ea/Ep  =  %    78.58 

#  =  14,800,  Ea        =lbs.  12.171 

Ea/Ep  =  %    79.80 

#  =  16,000,  Ea       =lbs.  13.325 

Ea/Ep  =  %    80.82 

This  table  shows  that,  other  conditions  being  equal,  the  highest  effi- 
ciency may  be  obtained  from  the  fuels  of  the  highest  heating  value; 
also  that  the  decrease  of  efficiency  due  to  rapid  rates  of  driving  is 
greatest  with  fuels  of  the  lowest  heating  value. 

Effect  of  Hydrogen  and  Moisture. — For  hydrogenous  fuels  and 
fuels  containing  moisture  some  deduction,  amounting  usually  to 
upwards  of  4%,  must  be  made  from  the  possible  efficiency  calculated 
by  the  formula,  on  account  of  loss  due  to  superheated  steam  in  the 
chimney-gases.  The  highest  efficiency  therefore  will  be  obtained  from 


vys  =     i  2.  3  4  5 

FIG.  79. — EFFECT  OF  HEATING  VALUE  OP  COAL  UPON  EFFICIENCY. 

anthracite,  although  the  semi-bituminous  coals  have  a  higher  heat- 
ing value  than  anthracite.  (See  Belation  of  Quality  of  Coal  to  Econ- 
omy, page  77.) 

Loss  of  Efficiency  due  to  Moisture  in  Air. — Each  pound  of  air 
supplied  to  the  furnace  carries  with  it  a  quantity  of  vapor  of  water, 
which  depends  on  the  temperature  of  the  air  and  its  relative  humidity. 
The  following  figures  show  the  amount  of  moisture  in  1  Ib.  of  air 
that  is  fully  saturated  at  the  several  temperatures  named : 


Temp.0  F 

Moisture,  Ib .  .  . 


32      I     42 
003741.00555 


52     ;|      62 
.00812    .01171 


72 
.01669 


82 
02353 


92 
.03288 


102 
.04555 


112    I    122 
06281 1.08629 


Each  pound  of  water  vapor  has  a  total  heat   (including  latent 
heat)  above  water  at  32°  of  from  1073.4  B.T.U.  at  32°  to  1113.4  at 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


301 


122°.  Assuming  that  the  vapor  is  carried  into  the  chimney  flue  as 
superheated  steam  at  612°  F.,  each  pound  then  has  a  total  heat  of 
1336.4,  and  the  differences  between  the  heat  per  pound  when  supplied 
to  the  furnace  and  when  passing  into  the  flue  are  as  follows : 


Initial  Temp.0  F 

Gain  in  heat  at  612°,  B.T.U 


32 
263 


42 
258.6 


52 


62 


254.1  I  249. 6 


72 
245.2 


82 
240.7 


92 
236.3 


102 


112 


231.9  227.4 


122 
223 


Multiplying  these  figures  by  the  moisture  per  pound  of  saturated 
air  gives  the  B.T.U.  lost  per  pound  of  saturated  air.  Multiplying  the 
product  by  the  number  of  pounds  of  air  supplied  per  pound  of  fuel 
gives  the  B.T.U.  loss  per  pound  of  fuel  due  to  moisture  in  the  air,  if 
the  air  is  saturated,  relative  humidity  =  100% ;  and  dividing  this 
product  by  the  heating  value  per  pound  of  fuel  gives  the  loss  of  ef- 
ficiency. Taking  the  heating  value  per  pound  of  fuel  at  15,000,  the 
temperature  of  the  chimney  gas  at  612°  F.,  and  the  pounds  of  air 
supplied  per  pound  of  fuel  at  12,  16,  20  and  24,  the  air  being 
saturated,  we  obtain  the  following : 

PER   CENT  LOSS   OF   EFFICIENCY   DUE   TO   MOISTURE   IN  SATURATED   AIR. 


Temp  °  F 

32 

42 

52 

62 

72 

82 

92 

102 

112 

122 

Air  per  Ib.  fuel  12 

0.08 
0.11 
0.13 
0.16 

0.11 
0.15 
0.19 
0.23 

0.17 
0.22 
0.28 
0.33 

0.23 
0.31 
0.39 
0.47 

0.33 
0.44 
0.55 
0.66 

0.45 
0.60 
0.76 
0.91 

0.62 
0.83 
1.04 
1.24 

0.85 
1.13 
1.41 
1.69 

1.14 
1.52 
1.90 
2.29 

1.54 
2.05 
2.57 
3.08 

"    16 
"    20 
"    .                 24 

For  lower  humidity  than  100%  the  loss  will  be  proportionately 
lower. 

For  lower  heating  value  of  the  fuel  than  15,000  the  loss  will  be 
proportionately  higher. 

Conclusions  from  a  Study  of  the  Diagrams. — The  values  of  effi- 
ciency given  in  the  tables  on  pages  297  to  300  are  plotted  on  the 
diagrams  accompanying  them.  In  Fig.  77  there  are  also  plotted 
the  values  of  the  highest  results  obtained  at  different  rates  of  evapor- 
ation in  the  boiler  tests  at  the  Centennial  Exhibition  (Philadelphia, 
1876),  and,  for  comparison,  some  of  the  lowest  results  at  different 
rates  of  evaporation  in  the  same  tests. 

A  study  of  the  diagrams  leads  to  several  important  conclusions : 

1.  The  results  of  seven  Centennial  tests,  F,  L,  E,  B,  S,  and  GGf 
which  are  the  highest  reliable  results  ever  obtained  with  anthracite 
coal  for  the  rates  of  evaporation  shown,  lie  a  little  below  the  curve  of 
R  =  0.1,  /  =:  20,  a  =  200. 


302  STEAM-BOILER  ECONOMY. 

2.  The  curve  of  R  =  0.1,  /  =  20,  and  a  =  100,  lies  so  much  above 
the  curve  of  these  Centennial  tests  as  to  make  the  value  a  =  100 
highly  improbable. 

3.  The  effect  of  radiation  on  the  evaporation  is  comparatively 
small  for  values  of  R  between  0.05  and  0.2   (which  is  probably  as 
high   a   range   as   is   found   in   practice   when   the   boilers   are   well 
covered)    when   the   rate   of   evaporation   is   over   3   Ibs.   per   square 
foot  of  heating  surface  per  hour,  but  it  increases  rapidly  at  low  rates 
of  evaporation. 

4.  The  effect  of  variations  of  a  within  the  limits  of  a  =  100  and 
a  —  300  increases  rapidly  with  the  increase  of  rate  of  evaporation; 
but  the  effect  of  increase  of  a  is  not  nearly  so  important  as  the  effect 
of  increase  of  /. 

5.  The  effect  of  increase  of  /,  which  is  a  measure  of  the  air-supply 
per  pound  of  combustible,  is  of  extreme  importance,  especially  at 
high  rates  of  driving.     With  R  =  0.1  and  a  =  200  the  effect  on  Ea 
of  increase  of  /  with  different  values  of  W/S  is  shown  in  the  following 
figures : 

/=20  /=30  /=35 

TF/S  =  2,#a  =  12.42  10.76  9.75 

"     =4,  "  =12.05  9.43  7.75 

"    =6,  "  =  11.47  7.89  5.55 

A  value  of  /  =  20,  corresponding  to  19  Ibs.  of  air  supplied  per  pound 
of  combustible,  is  about  as  low  as  can  be  obtained  in  practice  without 
incomplete  combustion  of  a  part  of  the  fuel,  resulting  in  some  CO  in 
the  furnace-gases.  The  rapid  decrease  in  economy  as  the  air-supply 
is  increased  shows  how  important  it  is  to  so  regulate  the  thickness 
of  the  bed  of  coal,  as  related  to  the  force  of  draft,  as  to  keep  the  supply 
of  air  at  or  near  19  Ibs.  per  Ib.  of  combustible. 

Value  of  c. — In  all  the  above  calculations  we  have  taken  c,  the 
specific  heat  of  the  flue-gases,  as  constant,  =  0.24.  The  actual  specific 
heat  of  a  mixed  gas  is  found  by  multiplying  the  percentage  by  weight 
of  each  constituent  by  its  specific  heat,  adding  the  products  and  divid- 
ing by  100.  The  specific  heats  of  the  constituents  of  flue-gases 
are,  according  to  Eegnault,  0,  0.2175;  N,  0.2438;  CO,  0.2479;  C02, 
0.217.  The  calculated  specific  heat  of  flue-gases  usually  ranges 
between  0.235  and  0.24.  If  0.235  were  used  instead  of  0.24  in 
computations  of  eq.  (13),  the  results  would  be  higher  by  about  half 
of  one  per  cent.  It  is  probabLe,  however,  that  the  figures  for  the 
specific  heat  of  the  constituent  gases  given  above,  which  are  those 


EFFICIENCY  OF  THE  HEATING  SURFACE.  303 

given  in  most  text-books  as  the  specific  heats  of  gases  at  ordinary 
atmospheric  temperatures,  are  much  too  low  for  hot  gases. 

If  the  specific  heat  is  taken  a  variable  increasing  as  some  func- 
tion of  the  temperature,  the  computation  would  be  extremely  difficult. 
In  view  of  the  inexactness  of  the  two  assumptions  made  in  establishing 
formula  (13),  viz.,  that  the  transmission  of  heat  is  proportional  to 
the  square  of  the  temperature  difference  (-between  the  hot  gases  and 
the  water)  and  2,  that  the  specific  heat  of  the  gases  is  a  constant,  the 
formula  and  the  tables  and  diagrams  derived  from  it  should  be  con- 
sidered only  as  empirical  and  tentative.  The  results  obtained  from  it, 
however,  show  a  remarkable  agreement  with  the  best  results  obtained 
in  modern  boiler  practice. 

See  Appendix,  Note  6,  page  340. 

Practical  Conclusions  derived  from  the  above  Theoretical  Dis- 
cussion.— Many  important  deductions  may  be  made  from  a  study  of 
the  figures  derived  from  equation  (13)  and  of  the  diagrams  plotted 
therefrom.  It  may  be  well  first  to  restate  the  notation  of  that 
formula : 

Ea  =  Ibs.  water  actually  evaporated  from  and  at  212°  (or  U.E.) 

per  Ib.  of  combustible ; 

Ep  =  theoretically  possible  evaporation  in  U.E.  per  Ib.  of  com- 
bustible, =  K+  970.4; 
Ea/Ep  =  efficiency,  usually  expressed  as  a  percentage; 

K  =  heating  value  of  the  fuel,  in  B.T.U.  per  Ib.  combustible; 
t  =  temperature  of  the  water  in  the  boiler,  minus  the  tempera- 
ture of  the  air-supply; 

c  =  specific  heat  of  the  gases,  taken  as  a  constant  =  0.24; 
/  =  Ibs.  of  gas  per  Ib.  of  combustible; 

R  =  radiation,  in  U.E.  per  sq.ft.  of  heating  surface  per  hour; 
W/S  =  rate  of  driving,  U.E.  per  hour  per  sq.ft.  of  heating  surface; 
a  =  an  experimental  coefficient  expressing  the  resistance  of  the 
plates  and  tubes  of  the  boiler  to  the  transmission  of  heat, 
together   with   certain   losses   of  efficiency  due  to  short- 
circuiting  of  the  gases,  to  eddies  of  cool  gas,  etc. 

The  formula  is 

K  -tcf 

K     ~  ac*f*      W 

Ea=  ^____    ....     (13) 


304  STEAM-BOILER  ECONOMY, 

The  fifst  deduction  from  the  study  already  made  is  that  the  effi- 
ciency of  a  boiler  is  an  exceedingly  variable  quantity,  depending  on 
no  less  than  six  variable  factors,  K,  t,  f,  R,  W/S,  and  a.  Only  one 
of  these  factors,  viz.  a,  is  related  to  the  construction  of  the  boiler  and 
to  the  condition  of  its  heating  surface,  and  this  only  partly,  for  to 
some  extent  it  depends  on  the  rate  of  driving,  since  short-circuiting  of 
the  currents  of  hot  gas  may  be  influenced  by  the  rate  of  driving.  The 
value  of  R  depends  upon  the  effectiveness  of  the  protection  of  the 
boiler  and  furnace  from  loss  by  radiation.  All  of  the  other  factors  are 
functions  of  the  conditions  under  which  the  boiler  is  operated. 

The  importance  of  the  factor  a  upon  the  efficiency,  as  shown  in 
the  diagram  Fig.  77,  leads  to  the  conclusion  that,  so  far  as  possible,  the 
metal  of  the  heating  surfaces  should  be  thin;  they  should  be  kept 
clean  inside  and  out;  the  gas-passages  should  be  so  constructed  that 
the  currents  of  hot  gas  will  pass  uniformly  over  the  whole  extent  of 
heating  surface,  avoiding  short-circuiting  and  eddies,  or  the  passage 
at  greater  speed  over  some  portions  than  over  others;  the  circulation 
of  water  should  be  sufficient  to  wipe  off  bubbles  of  air  or  steam  as  fast 
as  formed;  and  the  combustion  should  be  complete. 

The  effect  of  K  on  the  efficiency,  as  shown  in  Fig.  79,  indicates 
that  the  heating  value  of  a  fuel  is  not  exactly  a  measure  of  its  practical 
value.  For  a  rate  of  driving  W/8  =  3  we  have  found,  with  /  =  20 
and  a  —  200,  the  values  of  K  being  per  Ib.  combustible : 

For  K= 13,600  14,800  16,000 

Ea/Ep  =  per  cent 78.41  80.60  82.34 

KXEa/Ep= 10,664  11,929  13,174 

While  the  heating  values  are  in  the  ratio 91.9  100  108.1 

The  practical  values  are  in  the  ratio 89.5  100  110.4 

If  coal  of  14,800  B.T.U.  per  Ib.  is  worth  $1  per  ton,  coal  of 
13,600  B.T.U.  is  worth,  not  91.9  cents,  but  89.5  cents,  if  the  rate  of 
driving  of  the  boiler  is  3  Ibs.  per  sq.ft.  of  heating  surface  per  hour, 
and  still  less  if  the  rate  is  greater.* 

The  effect  of  the  rate  of  driving,  W/S,  shown  in  the  diagrams, 
indicates  that  for  practically  all  values  of  the  other  variables  the 

*The  calculation  is  based  on  /  =  20  in  each  case.  The  coal  of  #  =  13,600 
would  be  high  in  oxygen  and  water,  and  with  it  /  might  be  less  than  20  without- 
causing  CO  in  the  gases.  A  lower  value  of  /  would  cause  the  efficiency  to  be 
higher  than  in  the  figure  given  in  the  table.  The  coal  of  K  =  16,000  would  be 
high  in  hydrogen,  which  would  cause  a  decrease  in  efficiency  of  about  3  to  4%. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  305 

evaporation  and  the  efficiency  are  a  maximum  when  the  rate  of  driving 
is  about  2  Ibs.  evaporation  per  sq.  ft.  of  heating  surface  per  hour;  but 
that  under  fairly  good  conditions,  as  when  /  =  20,  a  =  200,  the 
efficiency  is  but  slightly  less  at  3  Ibs.  If  3000  Ibs.  of  water  per  hour 
are  to  be  evaporated,  a  boiler  of  1000  sq.  ft.  of  heating  surface  will  be 
almost  as  economical  of  fuel  as  one  of  1500  sq.  ft.,  provided  the 
boiler  is  well  constructed,  so  that  a  may  be  200  or  less,  the  coal  is  of 
good  quality,  say  K  =  14,800,  and  the  management  of  the  fire  and 
draft  good,  so  that  /  —  about  20 ;  but  if  these  conditions  are  unfavor- 
able, then  the  boiler  of  1500  sq.  ft.  may  be  much  more  economical 
than  one  of  1000  sq.  ft.  When  good  operating  conditions  are  obtain- 
able the  small  saving  in  fuel  by  the  larger  boiler  will  probably  be  more 
than  offset  by  its  greater  cost,  so  that  practically  boilers  pro- 
portioned for  a  rate  of  driving  of  3  Ibs.  per  sq.  ft.  of  heating  surface 
per  hour  will  give  about  the  maximum  economy  of  all  costs,  including 
\nterest  on  investment,  depreciation,  etc.  When  fuel  is  of  very  low 
cost,  as  near  a  coal-mine,  or  when  a  boiler  is  to  be  run  at  full  capacity 
only  a  few  hours  per  day,  as  in  electric-lighting  plants,  boilers  pro- 
portioned for  a  much  higher  rate  of  driving  may  be  the  most  econom- 
ical in  total  cost. 

The  effect  of  R  on  evaporation  is  seen  to  be  very  slight  at  all  rates 
of  driving  above  2  Ibs.,  but  it  increases  rapidly  at  lower  rates.  When 
the  rate  is  below  1J  Ibs.,  and  there  are  two  boilers  in  a  plant,  it  will 
usually  pay  to  shut  down  one  of  them,  driving  the  other  at  a  3-lb.  rate, 
thereby  saving  half  of  the  loss  due  to  radiation. 

The  effect  of  high  values  of  /,  or  excessive  air-supply,  is  seen  to  be 
more  important  than  that  of  any  other  of  the  variable  factors  in  the 
equation.  It  is  therefore  of  the  utmost  importance  to  so  regulate  the 
draft  and  the  firing  that  the  air-supply  shall  be  no  more  than  sufficient 
to  maintain  complete  combustion.  A  very  high  furnace  temperature 
is  generally  an  indication  of  the  best  furnace  conditions,  although  it 
is  possible  to  have  a  high  temperature  and  a  considerable  loss  of  heat 
due  to  incomplete  combustion.  (See  the  table  on  page  28  and  the 
diagram,  Fig.  1,  on  page  29.) 

The  effect  of  the  temperature  of  the  water  in  the  boiler  upon  the 
efficiency  is  not  important  within  the  limits  of  ordinary  steam-boiler 
practice ;  but  a  gain  of  about  8  per  cent  in  the  evaporation,  when  the 
rate  of  driving  is  about  3  Ibs.  per  sq.ft.  of  heating  surface  per  hour, 
might  be  effected  if  it  were  possible  to  have  the  water  in  the  boiler  of 
a  temperature  as  low  as  212°  F.  Boiler-tests  have  sometimes  been 


306  STEAM-BOILER  ECONOMY. 

made  with  the  water  evaporated  at  atmospheric  pressure.  Records  of 
efficiency  obtained  in  such  tests  are  not  a  fair  measure  of  the  efficiency 
which  would  be  obtained  at  customary  steam-pressures.  The  Centen- 
nial tests  were  made  with  steam  of  70  Ibs.  gauge  pressure,  correspond- 
ing to  t  —  about  250°.  If  they  had  been  made  with  steam  of  140  Ibs., 
the  evaporation  per  Ib.  of  combustible  would  probably  have  been 
0.25  Ib.  less  in  those  tests  which  gave  the  highest  results,  reducing 
their  record  of  about  12  Ibs.  from  and  at  212°  per  Ib.  combustible  to 
about  11.75  Ibs. 

Results  corresponding  to  f  =  20  and  a  —  200,  and  an  efficiency  of 
80  per  cent  are  rarely  possible.  The  highest  results  obtained  in  the 
Centennial  tests  are  shown  on  the  plotted  diagram,  and  no  higher 
results  with  anthracite  have  ever  been  obtained  in  competitive  tests 
made  by  disinterested  experts  since  1876 :  all  fall  below  80%  efficiency, 
and  considerably  below  the  plotted  line  of  /  =  20,  a  =  200,  and  t  = 
250°.  It  is  possible  to  obtain  a  value  of  a  as  low  as  200  in  a  boiler  so 
designed  and  proportioned  as  to  avoid  all  short-circuiting  of  the  gases, 
and  it  is  also  possible  to  obtain  nearly  perfect  combustion  with  /  as  low 
as  20  Ibs.  per  Ib.  of  combustible,  but  it  is  difficult  to  have  both  /  and  a 
at  these  low  values  at  the  same  time.  Boilers  must  be  designed  with 
flues  or  other  gas-passages  of  ample  area  to  insure  against  choking  of 
the  draft,  and  to  allow  of  the  boiler  being  driven  beyond  its  normal 
rating,  but  large  gas-passages  are  apt  to  lead  to  more  or  less  short- 
circuiting,  hence  to  inefficiency  of  some  portions  of  the  heating  sur- 
face, corresponding  to  high  values  of  a.  The  line  on  the  diagram  /— 
20,  a  =  200,  must  therefore  be  considered  as  one  which  may  some- 
times, under  the  most  favorable  conditions,  be  nearly  but  never  quite 
reached,  and  an  efficiency  of  80  per  cent  as  a  little  beyond  the  best 
result  that  may  be  reached  in  practice.  With  semi-bituminous  and 
bituminous  coal  there  is  a  necessary  loss  of  efficiency  due  to  the  hydro- 
gen in  the  coal,  and  the  consequent  loss  of  heat  in  superheated  steam  in 
the  chimney-gases.  This  loss  is  rarely  less  than  3  % . .  We  may  there- 
fore conclude  that  about  79%  is  the  highest  efficiency  that  can  be 
reached  in  practice  using  hand-fired  furnaces,  with  anthracite  coal 
and  76%  with  bituminous  or  semi-bituminous. 

Much  higher  figures  than  these  are  sometimes  published,  but  they 
are  due  either  to  errors  in  the  boiler  test  or  to  too  low  figures  for  the 
heating  value  of  the  coal. 

With  mechanical  stokers  and  with  the  air-supply  controlled  in  ac- 
cordance with  the  indications  of  gas  analyses  82%  may  be  considered 


EFFICIENCY  OF  THE  HEATING  SURFACE.  307 

the  maximum  limit  of  efficiency  in  boilers  not  provided  with  econo- 
mizers. 

The  theoretical  values  of  efficiency  given  in  the  foregoing  tables 
and  plotted  on  the  diagrams  are  all  based  on  the  supposition  that  the 
combustion  is  perfect  and  that  the  air-  supply  and  the  furnace  temper- 
ature are  constant.  It  is  impossible  to  realize  these  conditions  with 
hand-firing,  since  the  opening  of  the  fire-door  and  the  firing  of  fresh 
coal  always  chill  the  furnace.  The  fresh  coal,  if  small  in  size,  checks 
the  air-supply  to  some  extent  and  tends  to  make  the  combustion  im- 
perfect for  a  short  time  after  it  is  fired.  After  the  fresh  coal  has  been 
partly  burned  away  the  air-supply  is  apt  to  be  excessive.  All  these 
causes  tend  to  make  the  efficiency  less  than  that  given  by  the  theoret- 
ical calculation.  With  automatic  stokers,  however,  and  with  the  air- 
supply  checked  by  analyses  of  the  chimney-gases,  it  is  possible  to 
obtain  greater  uniformity  of  conditions,  and  consequently  a  closer 
approximation  to  the  theoretical  efficiencies. 

Low  Temperature  of  Furnace  may  cause  High  Flue  Temperature. 
—With  high  rates  of  driving  and  excessive  supply  of  air  per  pound  of 
fuel  a  large  proportion  of  the  heating  value  of  the  fuel  is  used  in 
heating  air  which  is  carried  into  the  chimney  instead  of  in  generating 
steam.  Excessive  air-supply  causes  not  only  a  low  temperature  of 
the  furnace,  but  it  may  also  cause  a  high  temperature  of  the  chimney- 
gases,  as  is  shown  by  the  following  calculation  :  Take  from  the  above 
tables  the  case  of  K  =  14,800,  c  =  0.24,  t  =  300,  a  =  200,  R  =  0.1, 
and  W/S  =  6,  with  four  different  values  of/,  viz., 

/=  ...............................       20  25  30              35 

Ea  =  lbs  .........................  ...  11.473  9.854  7.891  5.553 

Efficiency,  Ea/Ep  =  per  cent  ..........  75  .  23  _  64  .  61  51  .  74  36  .  41 

Elev.  of  temp,  of  fire,  Tl=K+cf=  .....      3083°  2467°  2056°  1762° 

We  have  ^  -  -~-^-,  whence  flue  temperature  T2  =  2\  f  1  -  ^Y 

J^P          J-i  \       -&P/ 

but  Ea'  is  what  the  evaporation  would  be  if  there  were  no  radiation. 
It  differs  from  Ea,  the  actual  evaporation,  by  the  quantity 

BE,        AW'-W_      BEP 

JUa    —  &a  —  JD&p  ~  ^^,          **  rr  Tjr  •"•**» 


1  4-  ±  1  +  — 

W  SR 

(derived  from  equations  7  and  11).    We  have,  therefore, 


308  STEAM-BOILER  ECONOMY. 

For  /  = 20       25  30     35 

Ea-EP= 0.195     0.171  0.144   0.112 

Ea'         = 11.668          10.025  8.035        5.665 

#a'-^  =  per  cent 76.51            65.73  52.68        37.14 

T2  =  T1(l-Ea'/Ep)  = : 724°              845°  973°         1108° 

The  calculation  assumes  that  there  are  no  air-leaks  through  the 

setting  between  the  furnace  and  chimney  which  would  lower  the 

temperature  of  the  chimney-gases  and  decrease  the  efficiency. 

At  low  rates  of  driving,  excessive  air-supply  does  not  cause  so 
great  a  rise  in  the  flue  temperature;  thus  for  W/S  =  Z,  and  other 
conditions  as  above,  we  have : 

For/      = 20                 25  30                  35 

Ea          = 12.422          11.651  10.765             9.754 

Ea+Ep  =  per  cent 81.45            76.39  70.59              63.96 

T7!           = 3083°             2467°  2056°              1762° 

Ea'-Ep= 0.624            0.589  0.550             0.507 

Ear        =  13.046          12.240  11.315           10.261 

Ea'+Ep  =  per  cent 85.54            80.26  74.19              67.28 

T2           = 446°              487°  533°                 577° 


Relation  of  Furnace  Temperature  to  Extent  of  Heating  Surface 

7 

, 

S 


required  for  Good  Economy.  —  From  the  formulas  Ea'  =  BEP  —  A 


B  =  —  ^  —  ,  and  A  =  ^  ,  ,  it  is  evident  that  the  actual  evapora- 
li  l\  —  t 

tion  per  pound  of  fuel,  for  a  given  rate  of  driving  W'/S,  depends  on 
the  furnace  temperature  T.  This  temperature  depends  not  only  on 
the  quantity  of  air  supplied  per  pound  of  fuel,  but  also  on  the  thor- 
oughness of  the  combustion  effected  by  it,  as  well  as  on  the  dryness  of 
the  coal  and  air  and  on  the  amount  of  direct  radiation.  An  air-supply 
of  18  Ibs.  per  Ib.  of  carbon,  making  nearly  19  Ibs.  of  gas,  will  usually 
produce  the  maximum  efficiency,  a  lesser  supply  tending  to  make 
the  combustion  imperfect,  and  a  greater  causing  excessive  dilution  of 
the  gases,  both  of  which  diminish  the  efficiency.  With  the  proper 
supply  of  air,  however,  combustion  may  still  be  imperfect  and  the 
temperature  low,  on  account  of  imperfect  mixing  of  the  air  with  the 
gas  distilled  from  the  coal,  irregular  firing,  too  small  space  for  com- 
bustion in  the  furnace,  or  other  causes. 

1.  Consider  a  case  in  which  combustion  is  perfect,  with  Ep  =  15, 
Ti  =  3000°,  t  =  300,  a  =  200,  c  =  0.24,  /  =20,  W'/S  =  3,  and 
radiation  negligible. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  309 

Ti-t       3000  -  300       __ 
~TT          "3000"         °'9; 

acf          200  X  0.24  X  20 
=  ~T^t  =          -2700-  °'356; 

W 

Ea'  =  BEP  -  A-g-  =  0.9  X  15  -  0.356  X  3  =  12.432. 

2.   With  other  conditions  the  same  as  above  let  TI  =  2000°,  being 
reduced  by  imperfect  combustion.     Then 


.EV  =  0.85  X  15  -  0.565  X  3  =  11.055. 

This  is  a  decrease  of  over  1  1  per  cent  in  evaporation. 

3.  Find  the  value  of  W'/S  which  with  TI  =  2000°  will  give  an 
evaporation  of  12.432. 

W  W 

Ea'  =  BEP-  A~~',     12.432  =  0.85  X  15  -  0.565^-; 
o  o 

whence  W'S  =  0.318  -  0.565  =  0.563. 

This  means  that  in  order  to  obtain  the  same  capacity  and  the  same 
economy  combined  from  a  boiler  with  a  furnace  temperature  of  2000° 
as  can  be  obtained  with  3000°,  under  the  conditions  named,  it  would 
be  necessary  to  increase  the  heating  surface  in  the  ratio  of  3  to  0.563, 
or  over  five  times.  The  case  is  still  worse  if  radiation  is  taken  into 
account,  for  the  loss  by  radiation  per  pound  of  fuel  burned  is  much 
greater  at  very  low  than  at  moderate  rates  of  driving.  Let  r  =  loss 
by  radiation,  in  units  of  evaporation  per  pound  of  fuel,  then  Ed  -f-  r 

W 

=  BEP  -  A-z-.     If  r  in  the  last  case  =  0.32,  then  Ea'  =  12.43  +  0.32 

o 

W 
=  12.75  -  0.565—    whence   W'/S  =  0;    that   is,    the    evaporation 

of  12.43  U.E.  per  Ib.  fuel  could  not  be  reached  by  any  enlargement  of 
heating  surface  whatever  if  the  furnace  temperature  were  as  low  as 
2000°. 

4.  Suppose  the  furnace  temperature  is  reduced  not  by  imperfect 
combustion  but  by  excessive  air-supply.     Let  /  =  30  Ibs.  and  T  = 
2000°. 


310 


STEAM-BOILER  ECONOMY. 


B  =  0.85  as  before;  A  = 


acf 


200  X  24  X  30 


=  0.847; 


Tl  -  t  1700 

Ea  ==  0.85  X  15  -  0.847  X  3  =  10.21  for  W'/S  =  3. 

5.  With/  -  30,  required  W'/S  to  make  Ep  =  12.43. 
12.43  =  0.35  X  15  -  0.847  W'/S] 
W'/S  =  (12,75  -  12.43)  -  0.847  =  0.37, 

a  figure  which  would  probably  be  reduced  to  0  by  radiation. 

Examples  3  and  5  show  that  high  furnace  temperature  is  even  a 
more  important  factor  of  economy  than  extent  of  heating  surface. 

Effect  of  Increasing  the  Heating  Surface. — Heat  Transmitted  by 
Successive  Portions  of  the  Surf  ace  .—Suppose  we  have  a  horizontal 
fire-tube  boiler,  Fig.  80,  with  an  external  furnace  in  which  com- 


FIG.  80. — BOILER  DIVIDED  IN  SECTIONS. 

bustion  is  completed  before  the  hot  gases  reach  the  heating  surface. 
Conceive  that  the  heating  surface  is  divided  by  vertical  planes  into  a 
number  of  equal  sections.  It  is  desired  to  find  the  temperature  at 
the  end  of  each  section,,  the  efficiency  of  each  section  in  transmitting 
heat,  and  the  efficiency  of  the  boiler  when  made  of  1,  2,  3,  etc.,  up 
to  20  sections,  the  amount  of  fuel  burned  per  hour  being  the  same 
in  each  case. 

For  convenience  of  calculation,  assume  that  the  boiler  has  50 
tubes,  each  of  1  ft.  interior  circumference,  and  that  each  section 
is  1  ft.  long  and  has  1  sq.  ft.  of  heating  surface.  The  combustible 
burned  per  hour  is  taken  at  244  Ibs.,  or  4.88  Ibs.  for  each  tube,  and 
its  heating  value  is  14,800  B.T.U.  per  Ib.  Assume  that  the  Aveight 
of  ga&es  per  Ib.  of  fuel  is  20  and  30  Ibs.  in  two  cases  considered, 
that  the  specific  heat  of  the  gases  is  0.24,  that  the  temperature  of 
the  water  in  the  boiler  is  300°  F.  above  the  temperature  of  the 
atmosphere,  and  that  the  value  of  the  experimental  coefficient  a 
is  200.  Considering  only  one  tube  we  have  then 

#  =  14,800;     ^-4.88;    c  =  0.24;    «  =  200;     ^  300;    /=  20 or 30; 
S  =  1,  2,  3,  etc.,  up  to  20.     Radiation  R  is  taken  as  0. 


EFFICIENCY  OF  THE  HEATING  SURFACE.  311 

The  temperature   (above  atmospheric)   of  the  gas  in  the  furnace, 
assuming  no  loss  by  radiation,  is 

T!  =  K+fc  =  14,800  -  4.8  or  7.2,   =  3080°  or  2056°. 

The  efficiency  of  a  boiler  of  any  number  of  sections,  that  is,  the 
ratio  of  the  heat  transmitted  by  it  to  the  heat  which  it  receives,  may 

E  '       (TA—t\2  —  rl\ 
be  found  by  formula  (5)  -^r=  -  - — ^.    For  the  first  section, 

fi    '  OTQA2    •    QAQA 

8  =  1,  we  have  •=£ 


E    1*1- 

27802-^-3080 
2780+  468~5 


8 


From  eqiiation 


-—-)  =  3080X0.6639  =2045°. 


Ep  T\  \       up  i ^ 

For  the  water  evaporated,  corresponding  to  any  given  efficiency^ 

we  have 


=  74.427— 


15.851;    JF'  =  4.88  X  15.251 


Tf 


In    the    way    described    above    the    following    results    have    been 
obtained : 


s 

T2 

Efficiency,  Per  cent 

w 

w/s. 

/  =  20. 

/=30. 

/=20. 

/  =  30. 

/=20. 

/  =  30. 

/  =  20. 

/=30. 

0 

3080° 

2056° 

1 

2045 

1705 

33.61 

17.08 

25.02 

12.71 

25.02 

12.71 

2 

1571 

1471 

49.00 

28.45 

36.47 

21.17 

18.23 

10.59 

3 

1300 

1304 

57.79 

36.58 

43.01 

27.22 

14.34 

9.07 

4 

1125 

1178 

63.47 

42.70 

47.24 

31.78 

11.81 

7.95 

5 

1001 

1079 

67.50 

47.52 

50.24 

35.37 

10.05 

7.07 

6 

910 

1001 

70.46 

51.31 

52.44 

38.19 

8.74 

6.36 

7 

844 

937 

72.60 

54.43 

54.03 

40.51 

7.72 

5.79 

8 

787 

884 

74.45 

57.00 

55.41 

42.42 

6.93 

5.30 

9 

741 

839 

75.94 

59.19 

56.52 

44.05 

6.28 

4.89 

10 

703 

800 

77.37 

61.09 

57  .  58 

45.47 

5.76 

4.55 

12 

645 

738 

79.06 

64.11 

58.84 

47.71 

4.90 

3.98 

14 

600 

689 

80.52 

66.49 

59.93 

49.49 

4.28 

3.53 

16 

566 

650 

81.62 

68.39 

60.75 

50.90 

3.80 

3.18 

18 

539 

618 

82.50 

69.94 

61.40 

52.05 

3.41 

2.88 

20 

517 

591 

83.22 

71.25 

61.94 

53.03 

3.10 

2.65 

The  results  may  be  summarized  as  follows :  A  boiler  is  made  up 
of  20  equal  sections  added  one  after  another.  A  constant  quantity 
of  fuel  is  burned  per  hour.  When  the  air  supply  is  such  as  to  make 


312 


STEAM-BOILER  ECONOMY. 


20  Ibs.  of  gas  per  Ib.  of  fuel  the  initial  temperature  is  3080°,  the 
temperature  at  the  end  of  the  first  section  is  2045°,  and  it  drops  as 
successive  sections  are  added,  to  517;  while  if  the  gases  are  30  Ibs. 
per  Ib.  of  fuel,  the  initial  temperature  is  only  2056°,  but  the  final 
temperature  at  the  end  of  the  20th  section  is  reduced  only  to  591°. 


»ouu 
2400 

rau 

2300 

na 

2200 

I 

2000 

\ 

10 

^^ 

.  —  -* 

—  —  ' 

80 

1900 

\ 
\ 

\ 

^ 



~o 

1800 

\ 

\ 
\ 

\ 

x 

^ 

-- 



—  * 

1700 

\ 
\ 

\ 

/ 

x 

5* 

.^ 

^--" 

-"" 

no 

\\ 

/ 

' 

^i^ 

>^xx 

5**  1*00 

\ 

\y 

§3  1400 

/ 

A 

x/ 

s 

§  1300 

I 

\ 

f, 

x  . 

10 

1200 

1 

\ 

1  100 

/ 

\ 

\ 

in 

1000 

j 

\ 

\ 

000 

: 

\ 

X 

°0 

800 

1 

X 

^ 

-2? 

-£*®^ 

^r- 

7QO 

>v- 

^ 

--^2 
» 

^ 

30 

10 

fsno 

^~^*^, 

"*"> 

•~~-^. 

•  —  ^_ 

-—. 

.^____ 

500 

—-   .. 



"•    — 



10  12  14 

Sq.  ft.  Heating  Surface  per  Tube 


16 


18 


FIG.  81. — INCREASE  OF  EFFICIENCY  AND  DECREASE  OF  FLUE  GAS  TEMPERATURE 
DUE  TO  INCREASE  OF  HEATING  SURFACE. 

The  efficiency  increases  as  the  sections  are  added,  from  33.61%  to 
83.22%  when/=  20,  and  from  17.08%  to  71.25%  when/=  30.  Six 
square  feet  of  heating  surface  with/  =  20  gives  a  greater  evaporation 
and  a  greater  efficiency  than  18  sq.  ft.  when/  =•  30,  and  7  sq.  ft.  when 
/=  20  gives  a  greater  evaporation  than  20  sq.  ft.  when/ =  30.  Increas- 
ing the  heating  surface  from  10  to  20  sq.ft.  increases  the  efficiency 
from  77.37  to  83.22%  or  5.85%,  when/  =  20,  and  from  61.09  to 
71.25%,  or  10.16%  when./=  30.  With  10  sq.  ft.  of 'heating  surface, 
/=  30  and  efficiency  =61. 09%, doubling  the  heating  surface  will  in- 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


313 


crease  the  efficiency  to  71.25%,  but  reducing  /  to  20,  without  increas- 
ing the  heating  surface,  will  increase  the  efficiency  to  77.37%. 

The  water  evaporated  per  hour  increases  from  25.02  in  one  section 
to  61.94  in  20  sections  when /=  20,  and  from  12.71  to  53.03  when 
/=  30.  The  successive  differences  in  the  figures  in  the  columns 
headed  W  show  the  amount  evaporated  by  each  successive  section. 
The  last  two  columns  show  how  the  rate  of  evaporation  per  square 
foot  of  heating  surface  decreases  as  the  sections  are  added. 

The  most  important  fact  to  be  learned  from  these  results  is  the 
great  falling  off  both  in  capacity  and  efficiency  when  the  air  supply 
is  increased  from  19  Ibs.  to  29  Ibs.  (corresponding  to  an  increase  of 


. 

•^ 

/ 

/ 

-I  jinn 

\. 

^ 

x 

'^ 

. 

y 

x 

\'/ 

% 

^ 

^ 

/ 

s^;. 

- 

<s^ 

^x 

^x 

1  4.00 

s.1'" 

/• 

v^- 

•^ 

X 

iqrin 

^ 

Kf^ 

'• 

/ 

X" 

\ 

^ 

r> 

1200 

> 

, 

<:''/ 

X 

^ 

~^' 

r. 

^ 

x 

\ 

0 

1000 

& 

? 

\ 

X 

X" 

^ 

^ 

qnfl 

"•c/ 

/ 

^x 

^^ 

X 

ROO 

A* 

^ 

x 

\ 

700 

/ 

/ 

\ 

fiOO 

* 

/ 

, 

x 

\ 

/ 

^ 

inn 

FIG. 


4          6          8         10        12        14        16        18        20        22        24        26 
Water  Evaporated  from  and  at  212°  per  sq.  ft.  Heating  Surface  per  Hour 

82.  —  RELATION  OF  FLUE  GAS  TEMPERATURE  AND  EFFICIENCY  TO  RATE 
OF  DRIVING. 


/  from  20  to  30)  per  pound  of  combustible.  With/=  20  a  rate  of 
driving  of  4.90  Ibs.  per  sq.  ft.  of  heating  surface  gives  an  evaporation 
of  58.84  Ibs.  and  an  efficiency  of  79.06%,  while  when/=  30,  the  same 
rate  of  driving  (4.89  Ibs.)  gives  an  evaporation  of  only  44.05  Ibs.  and 
an  efficiency  of  only  59.19%. 

The  figures  in  the  table  are  plotted  in  Fig.  81,  on  the  basis  of  the 
number  of  square  feet  of  heating  surface  per  tube.  The  figures  for 
efficiency  are  plotted  also  in  Fig.  82,  on  the  basis  of  the  rate  of 
evaporation  per  square  foot  of  heating  surface.  The  efficiency  figures 
for  the  larger  heating  surfaces  and  slower  rate  of  evaporation  per 
sq.  ft.  of  heating  surface  might  be  considerably  reduced  if  radiation 
had  been  considered. 

Chart  and  Table  Showing  Efficiencies  and  Flue  Temperatures 
for  Varying  Air  Supply  and  Rate  of  Driving.  —  Using  the  same  data 


314 


STEAM-BOILER  ECONOMY. 


as  those  given  above,  except  that  /  is  taken  at  18,  21,  24,  27,  30  and 
36  and  S  at  3,  4,  5?  6,  9  and  12,  the  following  table  has  been  calcu- 
lated and  Fig.  83  plotted  therefrom,  showing  how  with  a  constant 
weight  of  fuel  but  with  the  heating  surface  and  the  .air  supply  varied, 
the  efficiencies,  the  rates  of  driving  and  the  flue  temperatures  vary. 
With  radiation  taken  at  0,  the  chart  consists  of  two  sets  of  straight 
lines  crossing  each  other,  one  set  giving  the  heating  surface  and  the 
fuel  burned  per  hour  per  square  foot  of  heating  surface;  the  other 
giving  the  pounds  of  gas  per  pound  of  fuel.  At  the  intersections  of 
these  lines  'are  given  the  flue  temperatures  corresponding  to  the  sev- 
eral conditions.  Two  dotted  line  curves  are  given  in  addition,  show- 
100 

90 


01         2         34         56         7         8         9        10       11      12       13       14       15      16 
Rate  of  Driving,  Ib.  of  water  evaporated  from  and  at  212°  per  sq.  ft.  H.S.  per  hr. 

FIG.  83. — EFFECT  OF  AIR  SUPPLY  AND  RATE  OF  DRIVING  ON  EFFICIENCY. 
ing  the  efficiencies  with  /  =  18  and  /  =  30  when  a  radiation  factor 
R  =  0.1  is  used.  At  the  lower  right  hand  of  the  chart  there  is  a 
small  diagram  showing  the  relation  of  the  flue  temperatures,  T«, 
to  the  air  supply  with  different  amounts  of  heating  surface.  With 
large  heating  surface,  S  =  12,  the  temperature  increases  as  the 
air  supply  increases,  but  with  small  heating  surface  the  temperature 
is  a  maximum  when  /  is  about  24. 

The  formulae  required  are  repeated  here  for  convenience. 
Temperature  of  furnace,  T\  =  K  -=-  fc, 

™  .  Ea'         (T,  -  tY  +  Ti 

Efficiency, 


Ep 


acft'  ' 
S 


V 


EFFICIENCY  OF  THE  HEATING  SURFACE.  315 

Temperature  at  the  end  of  any  section,      T2  =  Ti(l  —  Ea/Ep). 
Water  evaporated,  W  =  F~  X  g^g^- 

The  chart  emphasizes  most  strongly  the  fact  that  high  efficiencies 
can  be  obtained  with  high  rates  of  driving  only  when  the  air  supply 
is  kept  at  the  lowest  figure  consistent  with  complete  combustion,  cor- 
responding to  f  =  18  or  thereabouts. 

FLUE  TEMPERATURES,   RATES  OF  DRIVING,   AND  EFFICIENCIES,   CORRESPONDING  TO 
VARYING    EXTENT    OF    HEATING    SURFACE    AND    VARYING    AIR    SUPPLY 


/  = 

18 
3426° 

21 
2936° 

24 
2569° 

27 

2284° 

30 
2056° 

36 
1713° 

c 

T2  = 

1210° 

1310° 

1326° 

1321° 

1304° 

1240° 

5=3 

Wi/S  = 

15.61 

13.74 

12.00 

10.46 

9.07 

6.85 

F/S-1.627J 

Ea/Ep  = 

62.94 

55.38 

48.37 

42.16 

36.58 

27.60 

5=4.5      ( 

T2  = 

1021° 

1073° 

1105° 

1122° 

1127° 

1105° 

F/S  =  1  .  084  j 

f  Wi/S  = 

11.61 

10.49 

9.43 

8.41 

7.48 

5.87 

Ea/Ep  = 

70.19 

63.45 

56.99 

50.57 

45.21 

35.48 

5=6          f 

T2  = 

874° 

925° 

963° 

987° 

1001° 

1005° 

F/S  =0.813] 

tWi/S  = 

9.24 

8.50 

7.75 

7.04 

6.36 

5.13 

Ea/Ep  = 

74.48 

68.51 

62.51 

56.77 

51.31 

41.35 

5  =9          ( 

Tz  = 

707° 

752° 

790° 

817° 

839° 

863° 

F/S  =0.  542  1 

Wi/S  = 

6.56 
79.34 

6.15 
74.40 

5.73 
69.26 

5.31 
64.18 

4.89 
59.19 

4.10 
49.60 

5=12        f 

Tz  = 

617° 

654° 

688° 

715° 

738° 

769° 

"                I 
F/S  =0.407  j 

Wi/S  = 

5.09 

4.82 

4.56 

4.26 

3.97 

3.42 

Ea/Ep  = 

82.01 

77.73 

73.21 

68.86 

64.11 

55.10 

Modification  of  Formula  (15)  for  Incomplete  Combustion  and  for 
Moisture. — Let  C,  H  and  M  be  respectively  the  percentages  of  carbon, 
hydrogen  and  moisture  in  a  fuel,  K  the  total  heating  value  per  pound, 
and  ,/  the  pounds  of  dry  gas  per  pound  of  fuel.  The  heat  per  pound 
of  fuel  that  is  available  in  the  furnace  for  raising  the  temperature 
of  the  gases  of  combustion  is  less  than  K  if  part  of  the  C  is  burned  to 
CO  instead  of  to  C02  and  it  is  further  diminished  by  the  amount  of 
the  latent  heat  of  the  steam  formed  from  the  hydrogen  and  moisture 
in  the  fuel. 

The  loss  of  heat  per  pound  of  fuel  due  to  incomplete  combustion 

CO 

of  the  carbon  is  101.5  C  X  ^r~t 

(u(J  -j-  Cw2 

spectively  percentages  by  volume  of  the  dry  gases.     The  loss  due  to 
the  latent  heat  of  steam  in  the  gases  is 

M)  X  970.4  -7-  100  «  970.4(0.09/7+  0.01J/), 


„  ,   in  which  CO  and   C02  are  re- 
\j(J< 


316  STEAM-BOILER  ECONOMY. 

i 

We  have,  therefore,  for  the  available  heating  value 

PO 

KI  =  JT-101.5  Onn   ,  "        -970.4(0.09#  +  O.OlJJf). 
L>U  -f-  UU2 

The  heat  lost  per  pound  of  fuel  in  the  gases  escaping  at  the 
temperature  (measured  above  atmospheric  temperature)  of  the  water 
in  the  boiler,  represented  in  equation  (15)  by  t  c  f  is  increased  by 
the  heat  of  the  superheated  steam  in  these  gases,  measured  above 
the  atmospheric  temperature  ta,  or 

(0.09#+  0.  01  M)  [212  -ta  +  970.4  -f  0.48(^  +  ^-212)]; 

but  the  loss  due  to  latent  heat,  970.4  B.T.U.  per  Ib.  steam,  has  already 
been  taken  account  of  in  the  furnace  losses,  and  the  remaining  loss  at 
the  temperature  t  -f-  ta  is 


&-0.52k-f  110.84). 

If  we  take  t  —  300  and  ta  =  62°  for  average  conditions,  this  reduces  to 

(0.09#  +  O.OUf)  X222, 

and  fc/i  =  tcf+  222(0.09#  +  O.OlM). 

If  t  =  300  and  c  =  0.24,  tc  =  72;  222  -=-  72  =  3.  08,  and  we  may  write 

fc/i  =  tc[f  +  3.08(0.09#  +  0.01  Jf), 
or  /i  =  /  +  0.  28#  +  0.  03  Jf, 

which  is  a  sufficiently  close  approximation  for  all  ordinary  values  of 
t  and  ta. 

Formula   (15)   thus  modified  for  incomplete  combustion  of  car- 
bon and  for  latent  heat  of  the  steam  in  the  gases  thus  becomes 


Ea        Ei-to  970.4   fljg2!2    W  ,     . 

' 


and,  similarly  formula  (16)  for  the  value  of  a  becomes 

70. 
K 


[     K.-tcf,        EJ  .  970.4     «!»/!»     W 
"  ' 


VI  1     i     7? 

A     I     1    -f    K-^r 


No  account  is  taken   in  the  above   calculation   of  any  loss  due 

to   unconsumed   hydrogen    or   hydrocarbons,   nor   of    absorption   of 

heat   by    decomposition    of   moisture    in   the    coal    by   the   reaction 


EFFICIENCY  OF   THE  HEATING  SURFACE.  317 

=  2H-J-CO.  Serious  losses  may  be  due  to  these  causes  if 
the  air  supply  is  deficient  and  the  furnace  temperature  low,  from 
the  firing  of  a  thick  layer  of  fresh  and  moist  coal,  or  if  the  combustible 
gases  are  chilled  by  the  surface  of  the  boiler  to  a  temperature  below 
that  of  ignition.  No  account,  either,  has  been  taken  of  the  loss  due 
to  moisture  in  the  air,  which  is  considered  on  page  300. 

Example. — Required  the  efficiency  of  a  boiler  using  moist  wood 
as  fuel,  the  wood  having  the  composition,  Ash  1 ;  Moisture  24 ;  C,  38 ; 
H,  5;  0,  32.  Heating  value  per  Ib.  6168  B.T.U.  Let  R=  0.1,  av  = 

W 
200,  C  =  0.24,  and  t=  300.     Solve  for  —  =  3,  4  and  6,  and/=  8  and 

12  Ibs.'per  Ib.  of  wood,  =  10.67  and  16  Ibs.  per  Ib.  combustible. 
/!=/  +  0.28tf  +  0.02Af=  10.12  and  14.12;  /i*=  102.4  and  199.4. 
A"x  =  K  -  970.4(0.09#  +  0.01J/)  =  5498. 

Ea      5498-300X0.24/1       970.4^     11.52/!*    W 
Formula  (18    — °  =  -  -=-       -^      —--,  X  ^     -^. 

E»        1  +  0.1^X6168 
Results  /  =  8  /  =  12. 

^=3  4  6  3  4  6. 

o 

f?  (per  cent)  =63.11       59.93      52.77         46.09       38.77      22.78. 
tip 

This  example  shows  that  there  is  a  rapid  loss  of  efficiency  with 
moist  fuel  at  increased  rates  of  driving  when  the  air  supply  is  even 
moderately  excessive.  The  theoretical  air  supply  required  is  0.38X 
11.52  +  (5  -4)  X  34.56=  7.834;  /  =  12  Ibs.  is  only  53%  in  excess. 

Meaning  of  the  Coefficient  a\. — The  coefficient  a±  is  an  empirical 
coefficient  of  performance  obtained  from  the  results  of  efficiency  tests 
in  which  the  following  values  are  known  or  assumed :  (1)  the  analysis 
and  the  heating  value  of  the  fuel;  (2)  the  analysis  of  the  waste 
gases;  (3)  the  rate  of  driving;  (4)  the  temperature  of  the  water  in 
the  boiler  above  atmospheric  temperature ;  ( 5 )  the  specific  heat  of 
the  gases;  (6)  the  loss  by  radiation;  (7)  the  efficiency.  It  takes 
into  account  the  loss  due  to  latent  heat  of  the  moisture  in  the  steam 
formed  from  the  combustion  of  the  hydrogen  and  the  moisture  in 
the  fuel,  and  the  loss  due  to  incomplete  combustion  of  the  carbon, 
these  losses  being  computed  from  the  analyses,  but  does  not  take 


318  STEAM-BOILER  ECONOMY. 

into  account  losses  due  to  the  escape  of  unburned  hydrogen  or  hydro- 
carbons, or  to  moisture  in  the  air.  It  may  be  considered  as  a  co- 
efficient of  resistance  of  the  boiler  surfaces  to  transmission  of  heat, 
and  its  value  will  be  increased  by  the  coating  of  these  surfaces  with 
scale  or  soot,  and  by  the  short-circuiting  of  the  gases,  which  renders 
a  portion  of  the  surface  ineffective.  Its  value  is,  moreover,  affected 
by  all  the  errors  of  measurement  of  test  and  by  the  errors  of  analyses 
and  of  inaccurate  sampling  of  the  fuel  and  of  the  gases,  and  by  fuel 
blown  out  of  the  chimney  if  no  record  is  made  of  it. 

The  value  of  the  coefficient  is  in  the  neighborhood  of  200  when 
the  boiler  performance  is  from  good  to  excellent.  Values  from  160 
to  240  may  be  obtained  in  duplicate  tests  in  which  all  the  conditions 
as  far  as  known  are  identical,  the  difference  between  individual  and 
average  values  being  due  probably  to  errors.  Values  above  300,  if 
not  due  to  errors,  represent  defective  performance  which  may  be 
due  to  short-circuiting  or  to  unclean  heating  surfaces. 

The  equation  for  the  value  of  %  may  be  solved  conveniently  with 
the  aid  of  a  table  of  four-place  logarithms,  as  in  the  following 
example : 

Let  K  =  14,800;  #1  =  14,200;  t  =  300;  c  =  0.24;  /i  =  18; 
W/S  =  3;  R  =0.1;  Ea/Ep  =  78  per  cent, 

ai  ==  [K(l  +  RS/W)  ~WP\  X  970.4c2/!2  W/S' 
Ki-ttft     =12,904,  log=  4.1107 

K  =  14,800,  log  =  4 . 1703 
1+RS/W  =  1.033,  log   =  0.0141 

Sum=  4.1844 

Difference  =  1.9263 

No.=  0  8440 

Subtract  Ea/EP  0 . 7800 


Quantity  in  brackets  =  0 . 0640 

log.=  2.8062 

.]og.Jr(JTi-#i)  =  8.2810 

7.0872 

log.  970. 4c2  =  1.7473 

log./!2        =2.5105 

log.  W/S      =0.4771 

4.7349 
Difference  =  2 . 3523 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


319 


Values  of  ai  Calculated  from  Results  of  Boiler  Trials. — From  the 

results  of  six  series  of  boiler  trials,  47  tests  in  all,  the  values  of  a\ 
have  been  computed  by  means  of  formula  (18).  The  general  results 
of  these  trials  are  given  in  Chapter  XVII.  They  include  13  tests 
of  Babcock  &  Wilcox  marine  boilers  built  for  the  IT.  S.  cruisers  "Cin- 
cinnati" and  "Wyoming;"  18  tests  of  a  locomotive  at  the  locomotive 
testing  laboratory  of  Purdue  University,  Lafayette,  Ind.,  11  with 
bituminous  and  7  with  semi-bituminous  coal;  and  16  tests  of  Stirling 
boilers  at  the  Delray  station  of  the  Detroit  Edison  Co.,  9  with  a  Roney 
stoker  and  7  with  a  Taylor  stoker.  The  following  table  gives  the 
values  of  a±  for  different  rates  of  driving,  W/S,  and  the  values  are 
plotted  in  Fig.  261,  page  622.  They  justify  the  use  of  the  figure  200 
as  the  approximate  average  value  of  at  under  the  best  conditions  of 
modern  practice. 

VALUES   OF   0i    IN   47   BOILER   TESTS 

Marine  Boilers. 


( 

Cincinnati. 

i 

SVyoming. 

No. 

W/S 

ai 

No. 

W/S 

ai 

1 

5.18 

241 

1 

3.88 

326 

2 

5.57 

209 

2 

6.43 

237 

3 

8.42 

255 

3 

9.03 

175 

4 

8.75 

197 

4 

10.52 

161 

6 

9.58 

359 

6 

10.52 

181 

5 

10.07 

150 

5 

14.76 

145 

7. 

13.67 

185 





Av  

204 

Av 

228 

Omitting  No.  1 

Av.'  .'.'.'.". 

180 

Omitting  No.  6 

Av  

206 

Locomotive. 


Bituminous  Coal. 

Semi-bituminous  Coal. 

No. 

w/s 

ai 

No. 

W/S 

ai 

12 

4 
11 
7 
10 
8 
3 
2 
5 
1 

Av  

7.02 
9.43 
10.07 
10.89 
11.26 
11.47 
11.51 
13.08 
13.18 
13.69 

203 
200 
154 
189 
158 
196 
198 
190 
168 
205 

186 

18 
9 
16 
15 
6 
14 
13 

Av 

5.12 
7.16 
9.30 
9.90 
10.82 
12.77 
13.30 

197 
157 
187 
193 
251 
189 
210 

198 

320 


STEAM-BOILER  ECONOMY. 


Stirling  Boiler. 


Honey  Stoker. 

Taylor  Stoker. 

No. 

W/S 

ai 

No. 

W/S 

01 

2 
5 
16 
1 
3 
6 
4 
17| 
18 

2.78 
3.24 
3.40 
3.63 
3.92 
5.20 
5.26 
6.67 
6.75 

274 
166 
184 
194 
258 
291 
261 
224 
221 

10 
8 
12 
7 
9 
14 
11 

Av.  . 

3.22 
3.72 
4.18 
5.22 
5.62 
6.40 
7.29 

251 
184 
210 
207 
237 
231 
256 

225  / 

Av  
Omitt'g  274 

and29i,'Av. 

230 
215 

Calculations  of  Efficiency  by  the  Revised  Formula  (18) . — Take 
a  Pittsburgh  bituminous  coal,  having  a  composition,  free  from  sul- 
phur and  ash,  of  83  C,  5.5  H,  8  0,  1.5  N",  and  2  Moisture,  and  a  heat- 
ing value  of  14,908  B.T.U.  per  Ib.fuel  =  15,222  B.T.U.  per  Ib.  com- 
bustible, and  assume  it  to  be  burned  with  different  quantities  of  air, 
as  in  the  table  below,  we  may  compute  the  weight  of  air  supplied 
per  pound  of  fuel  and  per  pound  of  carbon,  and  the  analysis  by 
volume  of  the  gases,  by  the  synthetic  method  shown  on  page  34,  giving 
results  as  follows : 


Case. 

Percent 
of  C 
Burned 
to  CO. 

Per  cent 
Excess 
Air. 

Dry  Gas 

per  Ib. 
Fuel 
=/. 

Dry  Gas 
per  Ib. 
Carbon. 

Analysis  of  Dry  Gas  by  -Volume. 

C02 

CO 

o  - 

N 

(1).. 

0 

0 
0 
0 
5 
5 

10 

20 

0 
20 
50 
100 
0 
20 
0 
0 

11.60 
13.83 
17.16 
22.72 
11.36 
13.23 
11.12 
10.65 

13.98 
16.66 
20.67 
27.37 
13.69 
15.93 
13.40 
12.83 

18.45 

15  30 
12.18 
9.10 
17.85 
15.18 
17.21 
15.88 

0 
0 
0 
0 
0.94 
0.80 
1.92 
3.97 

0 
3.56 
7.09 
10.57 
0 
3.12 
0 
0 

81.55 
81.14 
80.73 
80.33 
81.21 
80.90] 
80.87 

80.15 
.j 

(2) 

(3  .. 

(4)  : 

A  

B.  . 

C.... 

D  

H20  in  gases  per  Ib.  fuel  =  0.09#  +  O.Ollf,  in  all  cases  =  0.515. 
Case  (1)  is  an  ideal  but  not  a  practicable  case,  since  it  is  not 
possible  in  practice  to  burn  all  the  C  to  C02  without  excess  of 
air.  Cases  (2),  (3),  (4),  A  and  B  are  all  within  the  range  of  ordinary 
practice  (which  sometimes  shows  200%  or  more  excess  air)  and 
cases  C  and  D  represent  either  the  condition  of  too  heavy  firing  and 
choked  air  supply,  or  the  condition  existing  for  a  minute  or  two 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


321 


after  firing  of  fine  moist  slack  coal,  which  temporarily  chokes  the 
air  supply  and  causes  the  formation  of  a  great  volume  of  smoky  gas. 
Cases  2  and  A  represent  the  best  possible  practice,  reached  only 
when  all  conditions  are  most  favorable. 

Applying  formula  (18),  we  take ^  =  14,908;  £  =  300;  c  =  0.24;  R 
=  0.1 ;  «i  =  200;  /=  the  values  given  in  the  table;  K\  and  /i  =  values 
given  by  the  formulae  in  the  preceding  paragraph,  and  W/S  dif- 


"0          1          2          3         4          5         6          7          8          9         10        11         12        13        U 
W/s=Lbs.  Evaporated  from  and  at  212°  per  sq.  ft.  Heating  Surface  per  Hour 

FIG.  84. — THEORETICAL  EFFICIENCIES  UNDER  DIFFERENT  CONDITIONS. 
ferent  values  from  0.5  to   14,  we  obtain  the  theoretical  efficiencies 
given  in  the  table  below : 

THEORETICAL  EFFICIENCIES  WITH  PITTSBURGH  COAL  UNDER  DIFFERENT  CONDITIONS. 


Case  ... 

(1) 

(2) 

(3) 

(4) 

A 

B 

C 

D 

Per  cent  C  to 

CO 

0 

0 

0 

0 

5 

5 

10 

20 

Per  cent  ex- 

cess air.  .  . 

0 

20 

50 

100 

0 

20 

0 

0 

W/S  = 

EFFICIENCIES,    PER   CENT 

0.5 

74.76 

73.68 

72.05 

68.97 

72.53 

71.61 

69.77 

65.79 

1 

81.13 

79.78 

77.73 

73.72 

78.69 

77.54 

76.23 

71.34 

2 

84.06 

82.30 

79.60 

73.90 

81.53 

80.02 

78.98 

73.87 

3 

84.49 

82.34 

79.02 

71.72 

81.91 

80.09 

79.35 

74.16 

4 

84.24 

81.71 

77.79 

68.91 

81.64 

79.50 

79.09 

73.85 

6 

83.03 

79.76 

74.65 

62.60 

80.43 

77.65 

77.91 

72.64 

8 

81.47 

77.45 

71.17 

55.87 

78.87 

75.48 

76.39 

71.11 

10 

79.77 

75.01 

67.55 

49.20 

77.17 

73.15 

74.74 

69.45 

12 

77.99 

72.48 

63.86 

42.37 

75.41 

70.76 

73.02 

67.72 

14 

76.16 

69.92 

60.12 

35.48 

73.58 

68.32 

71.27 

65.97 

322 


STEAM-BOILER  ECONOMY. 


The  figures  in  the  above  table  are  plotted  in  Fig.  84,  which 
clearly  shows  the  great  falling  off  in  efficiency  at  high  rates  of 
driving  when  the  air  supply  is  excessive,  and  the  necessity  of  gas 
analysis  (or  of  a  C02  or  an  oxygen  indicator)  if  high  efficiencies 
are  to  be  obtained  at  high  rates  of  driving. 

Effect  of  duality  of  Coal  upon  Efficiency. — Calculations  have  been 
made,  using  formula  (18),  of  the  theoretical  efficiencies  obtainable 
from  five  different  kinds  of  coal  and  an  average  fuel  oil,  the  analyses 
of  which  are  given  below,  on  the  assumption  of  complete  combus- 
tion with  20  per  cent  excess  air  supply,  at  =  200,  t  =  300,  c  —0.24 
and  rates  of  driving  W/S  from  1  to  14  Ibs.  The  results  are  shown 
in  the  table. 

ANALYSES    OF    FUELS 


Anthracite  Dry  and 
Free  from  Ash. 

Semi-bit. 

Pittsburgh 
Ash  and  S 
Free. 

Illinois. 

Lignite. 

California 
Fuel  Oil. 

C            94  .  3 
H              2.3 
O               2.4 

N              1.0 

Moist.           1  .  7 
N.S.Ash     4.6 
C          85.0 
H            4.5 
O            3.2 

Moist.     2  .  0 
C        83.0 
H          5.5 
O          8.0 
N          1.0 

Moist.  10.8 
C      61.0 
H        4.2 
O        9.6 
N        1.2 
Ash,  S  13.2 

Moist.  27.0 
C  47.4 
H  3.3 
O  12.0 
N  1.0 

0.2 
84.9 
11.9 
1.9 
S  1.1 

B.T.U.  per  Ib.  15,000 

14,950 

14,908 

10,640  ' 

8250 

19,600 

RELATION    OF    EFFICIENCY    TO    QUALITY    OF    COAL. 


Rate  of 
Driving,  W/S 

l 

2 

3 

4 

6 

8 

10 

12 

14 

Anthracite.  .  . 
Semi-bit  
Pittsb^.  bit. 
Illinois  • 
Lignite. 

81.85 
80.41 
79.78 
78.28 
75.83 
78.78 

84.56 
82.96 
82.30 
80.59 
77.76 
81.61 

E 

84.71 
83.00 
82.34 
80.44 
77.51 
82.01 

fficienc 
84.16 
82.38 
81.71 
79.64 
76.52 
81.74 

ies 
82.39 
80.42 
79.76 
77.34 
73.98 
80.52 

80.25 
78.10 
77.45 
74.71 
70.90 
78.97 

77.95 
75.64 
75.01 
71.93 
67.79 
77.26 

75.59 
73.12 

72.48 
69.09 
64.62 
75.48 

73.19 
70.54 
69.92 
66.20 
61.40 
73.58 

Fuel  oil 

The  efficiencies  in  the  above  table  are  plotted  in  Fig.  85. 

Efficiencies  Obtained  in  Practice. — In  the  best  modern  practice, 
under  the  most  favorable  furnace  conditions,  the  highest  figures  in 
the  above  tables  have  almost  been  reached,  as  is  shown  in  the  chapter 
on  Eesults  of  Boiler  Tests.  A  few  tests  with  fuel  oil  have  shown 
figures  slightly  higher  than  those  given  above.  The  best  record  yet 
obtained  with  coal  is  that  of  the  ten  best  out  of  the  sixteen  tests 
at  the  Delray  station  of  the  Detroit  Edison  Co.,  reported^  by  D.  S. 
Jacobus  in  Trans.  A.  S.  M.  E.,  1911.  A  straight  line  drawn  through 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


323 


the  plotting  of  these  tests  corresponds  to  the  formula  E  =  81  — 1.33 
(W/8-3). 


.78 
§76 


Sfii 


64 


234  567  8  9          10         11         12         13 

Lbs.  Water  Evaporated  per  sq.ft.  Heating  Surface  per  Hour 

FIG.  85. — RELATION  OF  EFFICIENCY  TO  QUALITY  OF  COAL. 


T 


The  Straight-line  Formula  for  Efficiency. — An  examination  of 
the  curves  in  Fig.  84  shows  that  when  the  rate  of  driving  is  in 
excess  of  3  Ibs.  per  sq.  ft.  of  heating  surface  per  hour,  and  the 
effect  of  the  radiation  loss  is  therefore  of  small  importance,  the 
curves  become  approximately  straight  lines,  the  formula  of  which  is 
E  =  Emax  —  C(W/S  —  3),  in  which  E  is  the  efficiency  at  any  rate  of 
driving  above  W/S  =  3,  Emay_  is  the  efficiency  when  W/S  =  3, 
and  C  is  a  constant  which  depends  on  the  quality  of  the  coal  and 
on  the  furnace  conditions.  Taking  from  the  curves  on  page  321  the 
efficiencies  at  W/S  =  3  and  W/S  =  14  and  calculating  the  value  of 
C  in  the  above  equation  of  a  straight  line  between  these  points,  we  ob- 
tain the  following  formulae  for  efficiency  for  the  several  cases  named : 


Case 

Per  Cent 
C  to  CO2 

Per  Cent 

Excess  Air. 

Formula 

1 

0 

0 

#=84 

5-0.76(^/^-3) 

2 

0 

20 

#=82 

3  —  1  .  \3(W/S  —  3) 

3 

0 

50 

#  =  79 

O  i  72,(W/S  3) 

4 

0 

100 

#  =  71 

7-3.290F/S-3) 

A 

5 

0 

#=81 

9-0.76(TF/S-3) 

B 

5 

20 

#=80 

1  —  1  .  07(W/$  3) 

C 
D 

10 
20 

0 
0 

#  =  79 
#  =  74 

4-0.73(^/^-3) 
2-0.74(TF/£-3) 

324  STEAM-BOILER  ECONOMY. 

Efficiencies  calculated  from  these  formula?,  for  values  of  W/S  above 
3,  are  in  all  cases  within  1  per  cent  of  those  given  in  the  table,  always 
lower,  as  the  curves  plotted  from  the  figures  in  the  table  lie  a  trifle 
above  the  lines  of  the  straight-line  formula. 

The  figures  given  the  table  represent  the  maximum  results  that 
can  be  obtained  under  the  several  conditions  named,  and  they  make 
no  allowance  for  moisture  in  air  nor  for  unburned  hydrogen  and 
hydrocarbons.  In  practice  it  is  not  to  be  expected  that  figures  quite 
as  high  as  these  can  be  obtained.  The  nearest  approach  to  them 
in  any  long  series  of  tests  in  which  the  greatest  precautions  were 
taken  to  secure  accuracy,  are  those  given  in  the  report  of  the  tests 
made  by  Dr.  D.  S.  Jacobus  at  the  Delray  station  of  the  Detroit 
Edison  Co.,  in  1911.  (Trans.  A.  S.  M.  E.,  vol.  33.)  The  ten  best 
tests  out  of  sixteen  give  the  formulae  E  =  81  —  1.33  ( W/S  —  3) . 

The  straight  line  formula?  corresponding  to  the  curves  in  Fig.  85, 
showing  the  theoretical  efficiencies  with  different  kinds  of  fuel  are  as 
follows : 

Anthracite #=84.7-1.05(TF/S-3) 

Semi-bituminous #=83.0-1.13(TF/S-3) 

Pittsburgh  bituminous #  =  82.3-1.13(TF/S-3) 

Illinois  bituminous #=80.4-1.2907/3-3) 

Lignite E  =  77.5-lA6(W/S-3) 

Fuel  oil E  =  82. 0-0. 77 (W/S -3) 

Deductions  from  the  Straight-line  Formula.—  If  we  take  the  formula 
obtained  from  the  ten  best  tests  at  Detroit,  E  =  81  —  1.33(  W/S—  3)  as 
representing  the  maximum  results  that  may  be  expected  from  any 
type  of  boiler  (not  provided  with  an  -economizer)  when  all  conditions, 
such  as  quality  and  dryness  of  coal,  abundant  volume  of  combustion 
space,  uniformity  of  depth  of  fire,  air  supply,  etc.,  are  most  favorable, 
then,  by  calculation  from  the  formula  the  following  results  will 
be  obtained  for  different  rates  of  driving.  It  is  assumed  for  the 
purpose  of  the  calculation  that  the  fuel  burned  per  hour  is  a  constant 
quantity,  sufficient  to  evaporate  100  Ibs.  of  water  per  hour  from  and 
at  212°  if  the  efficiency  =  100%.  For  any  other  efficiency  the 
pounds  evaporated  =  per  cent  efficiency,  or  W  =  E;  then  W  =  84  — 
1.Z3W/S. 

In  ordinary  practice  the  figures  given  in  the  table  for  E  when  W/S 
=  10  to  20  can  rarely  be  obtained,  on  account  of  the  difficulty  of  pro- 
viding a  sufficiently  large  volume  of  combustion  chamber  for  the 
complete  burning  of  the  gases  and  of  providing  a  grate  surface  large 
enough  to  develop  the  capacity  without  having  an  excessive  draft 
pressure  which  will  blow  unburned  fuel  into  the  chimney. 


EFFICIENCY  OF  THE  HEATING  SURFACE. 


325 


RELATION  OF  EFFICIENCY  TO  RATE  OF  DRIVING  UNDER  BEST  FURNACE  CONDITIONS. 


w/s 

S/H.P. 

E  or  W. 

S 

F 

W/F 

3 

11.50 

81.00 

27.00 

1.235 

8.10 

4 

8.62 

79.67 

19.92 

1.255 

7.97 

5 

6.90 

78.34 

15.67 

1.276 

7.83 

6 

5.75 

77.01 

12.84 

1.299 

7.70 

7 

4.93 

75.68 

10.81 

1.321 

7.57 

8 

4.31 

74.35 

9.29 

1.345 

7.43 

9 

3.83 

73.02 

8.11 

1.369 

7.30 

10 

3.45 

71.69 

7.17 

1.395 

7.17 

11 

3.14 

70.36 

6.40 

1.421 

7.04 

12 

2.87 

69.03 

5.75 

1.449 

6.90 

13 

2.65 

67.70 

5.21 

1.477 

6.77 

14 

2.46 

66.37 

4.74 

1.507 

6.64 

15 

2.30 

65.04 

4.34 

1.537 

6.50 

16 

2.16 

63.71 

3.98 

1.570 

6.37 

17 

2.03 

62.38 

3.68 

1.603 

6.24 

18 

1.92 

61.05 

3.39 

1.638 

6.10 

19 

1.82 

59.72 

3.14 

1.674 

5.97 

20 

1.72 

58.39 

2.92 

1.712 

5.84 

W/S  =  evaporation  from  and  at  212°  per  sq.ft.  heating  surface  per  hour. 
$/H.P.  =  sq.ft.  of  heating  surface  per  horsepower. 
E  =  per  cent  boiler  efficiency. 

S  =  sq.ft.  of  surface  required  to  evaporate  W  Ibs.  when  efficiency  =E. 
F  =  relative  quantity  of  fuel  required  if  1  Ib.  represents  an  efficiency  of 

100  per  cent,  =  reciprocal  of  (E  +  1QQ). 

W/F= relative  water  evaporated  per  Ib.  of  fuel  if  W/F  =  W  Ibs.  when  E  = 
100  per  cent. 

A.  Blechynden's  Experiments  on  Transmission  of  Heat  through 
plates  from  hot  gases  on  one  side,  to  water  on  the  other.*  In  these 
experiments  the  water  was  contained  in  a  cylindrical  iron  vessel  of 
tinned  iron  plate,  24  W.  G.  in  thickness,  with  the  steel  plate  to  be 
tested  soldered  in  the  bottom.  The  vessel,  .protected  from  radiation 
by  air-spaces  and  asbestos  felt,  was  placed  above  a  fire-brick  furnace, 
the  lower  half  of  which  was  filled  with  asbestos  lumps  or  balls,  covered 
with  wire  gauze.  Jets  of  gas  were  burned  among  these  balls,  gener- 
ating a  high  temperature  in  the  products  of  combustion  in  the  upper 
part  of  the  furnace.  The  hot  gases  were  allowed  to  escape  through 
four  small  horizontal  pipes  at  the  top  of  the  furnace,  on  four  sides,  so 
that  the  plate  was  exposed  on  its  bottom  surface  to  hot  gas  at  a 
•practically  uniform  temperature. 

Experiments  were  made  on  five  plates  of  different  thicknesses,  viz., 
plate  A,  originally  1.1875  in.  thick,  and  reduced  in  four  successive 
operations,  by  machining,  to  0.125  in.  thick;  plate  B,  four  thick- 

*  Trans.  Inst.  Naval  Architects,  1894;  also  Donkin's  "  Heat  Efficiency  of 
Steam-boilers,"  p.  145. 


326 


STEAM-BOILER  ECONOMY. 


nesses,  from  0.4688  in.  thick  to  0.1562  in.  thick;  plate  C,  0.8125  in.; 
plate  D,  0.5  in.;  plate  E,  1.1875  in.,  and  0.1875  in.  Plates  A,  B 
and  D  had  one  side  machined,  and  the  other  side  (that  exposed  to  the 
fire)  left  with  the  natural  surface  as  it  came  from  the  mill.  Plate  C 
had  both  sides  untouched,  and  plate  E  both  sides  machined. 

The  temperature  of  the  furnace  was  determined  by  a  Siemens 
copper-ball  pyrometer.  In  some  cases  an  iron  ball  was  used  instead. 
The  specific  heats  of  both  were  compared  with  that  of  a  piece  of  plati- 
num, and  the  temperatures  recorded  depend  upon  Pouillefs  determin- 
ation of  the  specific  heat  of  platinum,  as  in  the  following  table: 


Temp.  C. 

Temp.  F. 

Platinum, 
Sp.  Ht. 
(Pouillet). 

Iron, 
Sp.  Ht. 

Copper, 
Sp.  Ht. 

Between  0  and    100  .  . 
0    '        300  
0    '        500  
"         0    '         700 

32  and    212 
32    '        572 
32    '        932 
32    '      1292 
32    '      1832 
32    '      2192 

0.0335 
.0343 
.0352 
.0360 
.0373 
.0382 

0.1095 

.1189 
.1279 
.1374 

0.0961 
.0997 
.1032 
.1068 
melts. 

<  < 
<  < 

0    '      1000  

0    '      1200  

The  following  results  were  obtained  in  the  experiments:  T  —  / 
being  the  difference  between  the  temperature  F,  of  the  gas  below 
the  plate  and  the  water  above  it,  q,  the  quantity  of  heat  transmitted 
in  British  thermal  units  per  hour  per  square  foot,  and  a,  coefficient 
of  transmission  calculated  from  the  formula 


-  t\2 


(T-t) 


-   t\2 


or     a  = 


(T-t) 


PLATE    A. 


Thickness, 
Inch. 

1.187  ( 

T-t  = 
a  = 

T-t  = 



848 
66.6 

626 

993 
66.8 

788 

1,013 
66.3 

913 

1,213 
64.7 

1,058 

1,228 
61.6 

1,233 

1,278 
61.0 

0.75   < 

a  = 

57.2 

56.9 

56.9 

55.2 

56.1 

T-t  = 

563 

708 

963 

1,148 

0  .  562  | 

a  = 
T-t  = 

47.2 
503 

49.1 
646 

47.7 
723 

44.6 

828 

893 

978 

0.25   ( 

a  = 

42.6 

45.2 

44.0 

44.5 

44.2 

42,3 

0.125  | 

T-t  = 

a  = 

738 
44.7 

908 
43.7 

993 
41.1 

1,083 
42.5 

1,123 
41.2 

1,133 
41.5 

1,138 
41.3 

1,318 
38.5 

EFFICIENCY  OF   THE  HEATING  SURFACE. 


327 


PLATE  B. 


Thickness, 

Inch. 

T-t  = 

413 

638 

643 

993 

1,028 

1,123 

1,128 

1,148 

0  .  469      < 

a  = 

39.8 

44.3 

44.2 

41.9 

41.4 

41.1 

41.2 

41.3 

OO*7  C 

T-t  = 

650 

656 

958 

968 

1,108 

1,288 

1,308 

.375     < 

a  = 

44.3 

41.4 

40.9 

42.3 

41.0 

40.0 

39.7 

OOK 

T-t  = 

373 

513 

773 

823 

848 

855 

1,108 

1,128 

1,268 

.25 

a  = 

38.7 

40.1 

40.7 

39.3 

39.3 

38.4 

39.1 

38.4 

36.7 

0.156     • 

T-t  = 

a  = 

543 
39.0 

738 
40.2 

973 

38.4 

1,058 

38.7 

1,123 
38.3 

1,248 
38.2 

1,263 
37.4 

0.812 


0.5 


PLATE  C. 
652 

54.9 


763 
53.6 


PLATE  D. 


439 

45.2 


755 
43.2 


738 
41.6 

PLATE  E. 


744 
40.8 


773 
52.4 


768 
42.2 


778 
58.0 


847 
44.3 


778 
54.2 


879 
41.3 


848 
57.6 


910 
40.6 


( 

T-t- 

301 

440 

644 

1  073 

1.187  < 

a  — 

62  9 

70  0 

79  4 

71  3 

[ 

T  —  t- 

322 

559 

743 

1  128 

0.187  <^ 

a=  .  . 

52.4 

52.1 

53  .  5 

51  1 

AVERAGE  VALUES  OF  THE  COEFFICIENT  a. 


Plate  A,  Thickness 

1  .  1875  in. 

0.75  in. 

0.5625  in. 

0.25  in. 

0.125  in. 

a  = 

64.5 

56.5 

47.1 

43.8 

41.9 

Plate  B,  Thickness 

0.4687 

0.375 

0.25 

0.156 

a  = 

41.9 

41.4 

39.0 

38.6 

Plate  C,  Thickness 

0.8125 

a  = 

55.1' 

Plate  D,  Thickness 

0.5 

a  = 

42.4 

Plate  E,  Thickness 

1  .  1875 

0.1875 

a  = 

71.9 

52.3 

Mr.  Blechynden  says :  "The  broad  general  fact  is  evident  that  the 
heat  transmitted  through  any  of  the  plates  per  degree  of  difference  of 
temperature  of  the  water  and  the  fire  is  proportional  to  that  differ- 
ence ;  or  In  other  words,  the  heat  transmitted  is  proportional  to  the 
square  of  the  difference  between  the  temperature  at  the  two  sides  of 
the  plate,  or 


Heat  transmitted  per  sq.  ft. 


=  a  constant 


(Difference  of  temperature)2 
for  each  plate  within  the  limits  of  the  experiments." 


328  STEAM-BOILER  ECONOMY. 

Mr.  Blechynden  gives  this  constant,  or  modulus,  for  each  plate. 
It  is  the  reciprocal  of  the  coefficient  a,  which  has  been  calculated  by 
the  author  from  the  average  results,  for  the  purpose  of  comparing  it 
with  the  similar  coefficient  used  by  Rankine  and  others,  and  adopted 
in  the  preceding  discussion  on  the  efficiency  of  heating  surface. 

Mr.  Blechynden  further  says:  "The  table  shows  that  there  is  a 
general  rise  in  the  value  of  the  moduli  [a  decrease  of  a}  with  decrease 
of  thickness,  but  there  are  considerable  irregularities  in  the  curves 
joining  the  various  points  for  each  plate.  This  is  perhaps  no  more 
than  might  be  expected,  because  of  the  great  difficulty  of  machining 
all  the  surfaces  to  the  same  degree  of  smoothness,  and  notwithstand- 
ing the  precautions  taken,  the  difficulty  in  maintaining  the  surfaces 
uniformly  clean.  It  was  found  that  the  very  slightest  traces  of  grease 
caused  a  very  large  fall  in  the  rate  of  transmission;  even  wiping  the 
surface  of  the  plate  with  a  piece  of  rag  or  waste  was  sufficient  to 
influence  the  result  detrimentally.  That  the  smoothness  of  the  sur- 
faces was  an  important  factor  will  be  readily  seen  when  the  position 
of  the  points  for  the  plate  E  are  compared  with  the  others.  The  dif- 
ferences are  due  to  A  and  B  having  the  same  receiving  surface  as 
from  the  mill,  while  E  was  very  smoothly  machined. 

"The  results  of  these  experiments  certainly  point  to  the  conclusion 
that  the  thinner  the  plates  forming  part  of  the  heating  surface  of  a 
boiler  the  higher  should  be  the  boiler  efficiency,  always  provided  that 
the  plates  are  clean,  but  it  will  be  evident  that  if  the  plates  be  coated 
with  a  covering  of  scale,  or  some  bad  conductor,  then  the  less  must 
be  the  influence  of  the  thickness  on  the  efficiency,  while  with  a  thick 
coat  of  oil  the  influence  might  become  practically  unimportant.  The 
fact  that  the  heat  transmission  is  proportional  to  the  square  of  the 
difference  of  temperature  of  the  two  sides  of  the  plate  shows  the 
importance  of  high  furnace  temperatures." 

The  average  values  of  the  coefficient  a  obtained  from  Blechynden's 
experiments  have  been  plotted  in  the  adjoining  diagram,  Fig.  86.  It 
will  be  seen  that  each  plate  has  a  law  of  rate  of  transmission  of  its  own. 
Plates  A  and  C  have  about  the  average  values  for  the  different  thick- 
nesses, and  a  line  plotted  from  the  formula  a  =  40  +  %0t  is  near  to  all 
the  values  obtained  from  plate  A.  The  formula  a  =  40  +  2Qt  =b  10 
covers  the  whole  range  of  the  experiments. 

The  very  low  values  of  a  deduced  from  Blechyn  den's  experiments, 
viz.,  38.6  to  71.9,  as  compared  with  the  values  200  to  400,  commonly 
obtained  in  steam-boiler  tests,  are  no  doubt  due  to  the  exceptionally 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


329 


favorable  conditions  under  which  his  experiments  were  made,  all 
portions  of  the  plate  being  clean  and  equally  exposed  to  radiation 
and  to  contact  with  the  hot  gases,  while  in  steam-boilers  only  a  small 
fraction  of  the  heating  surface  receives  radiation  from  the  incan- 
descent fuel  or  from  glowing  fire-brick,  the  surface  is  apt  to  be  more 
or  less  covered  with  soot,  dust,  scale,  or  grease,  and  the  whole  heating 


75 


70 


C65 

eo 


40 


•* 


-*< 


025 


050  0.75  100 

Thickness  of  Plate,  Inches. 


125 


FIG.  86. — VALUES  OF  a,  FROM  BLECHYNDEN'S  EXPERIMENTS. 

surface  is  not  equally  effective,  part  of  it  being  short-circuited  and  in 
contact  with  eddies  of  comparatively  cool  gas. 

Durston's  Experiments  on  the  Transmission  of  Heat  through 
Plates.* — A.  J.  Durston  describes  some  experiments  made  to  deter- 
mine the  temperature  of  the  hot  side  of  a  plate,  exposed  to  hot  gases, 
when  the  other  side  was  covered  with  boiling  water.  The  tempera- 
ture was  determined  by  the  melting  of  fusible  solders  on  the  hot  side 
of  the  plate.  The  following  is  a  summary  of  the  results : 

1.  Temperature  of.  hot  side  of  a  clean  plate  exposed  to  gases  at 

about  1500°  F. about  240°  F. 

2.  Same  with  a  layer  of  grease  ^  in.  thick  over  inside  of  vessel. .     "      330° 

3.  Temperature  at  the  centre  of  thickness  of  a  plate between 

290°  and  336° 

4.  Loss  of  efficiency  of  heating  surface  of  boiler-tubes  due  to  a 

thin  coating  of  grease,  8  to  15  per  cent;   mean  of  several 
experiments,  11%. 

5.  Temperature  of  hot  side  of  plates  where  boiling  water  in  an 

open  vessel  under  various  conditions;   a  flanged  dish  2  ft. 
diameter,  2j  in.  deep,  j  in.  thick: 

*  Trans.  Inst.  Naval  Architects,  1893,  also  Donkin,  "  Heat  Efficiency  of 
Steam-boilers,"  p.  157. 


330 


STEAM-BOILER  ECONOMY. 


Temperature 
of  Fire. 

Temp.  Hot 
Side  of  Plate. 

Clean  fresh  water  

2200° 

280° 

Mineral  oil  gradually  added  up  to  5%. 

2300° 

310° 

Fresh  water  with  1\%  of  paraffine  

2100° 

330° 

Fresh  water  with  2|%  of  methylated  spirits 

2500° 

300° 

A  greasy  deposit  j£  in.  thick  on  the  plate.  .  . 
Other  experiments  with   greasy   deposits 

2500° 

about  550° 

showed  that  the  temperature  varied  greatly, 

depending  on  the  nature  and  thickness  of 

the  deposit. 

6.  Temperature  of  plates  when  boiling  water  in  a  closed  vessel  at  a 
higher  temperature  than  212°;   using  clean  water: 


Temp.  Hot 
Side  of  Plate. 

Temp,  of 
Water. 

Difference. 

Over  Bunsen  burner  

430° 

363° 

67° 

Over  blast  forge,  full  blast  

430° 

344  5° 

85   5° 

7.  Same,  bottom  of  vessel  coated  with  grease  : 
Over  forge-fire,  grease  1/16  in.  thick 

510° 

359° 

151° 

Over  grease  drier,  or  earthier  

550° 

351° 

199° 

Over  and  spreading  the  grease  up 

the  sides  of  the  vessel  

617° 

80° 

537° 

8.  Experiments  to  determine  whether  at  higher  steam  pressures  there  is  any 
marked  addition  to  the  excess  of  temperature  of  the  hot  side  of  the  plate 
over  that  of  the  water  showed  no  marked  addition. 

Effect  of  Circulation  upon  Economy. — In  the  above  discussions 
concerning  the  several  conditions  which  have  an  influence  on  the 
economy  of  a  steam-boiler,  nothing  has  been  said  of  the  effect  of  cir- 
culation of  the  water.  It  is  contended  by  some  writers  that  some 
boilers  have  a  more  active  circulation  of  water  than  others,  and  that 
the  transmission  of  heat,  and  therefore  the  efficiency  of  the  heating 
surface,  is  greater  the  more  rapid  the  circulation;  but  the  author  is 
not  aware  that  this  view  is  supported  by  the  results  of  trials  of 
steam-boilers.  It  is  well  known  that  a  steam-radiator  used  for  heat- 
ing air  transmits  a  .vastly  greater  quantity  of  heat  when  the  air  is 
blown  upon  by  it  by  a  fan  than  when  the -air  surrounding  it  is  com- 
paratively still — that  is,  merely  moving  upward  at  the  velocity  of  the 
ascending  column  of  heated  air;  also  that  a  coil  used  for  heating 
water  is  more  effective  when  the  water  is  given  a  rapid  motion;  the 
reason  being  that  the  rapid  circulation  of  the  air,  or  water,  constantly 
removes  from  the  heating  surface  the  heated  body  and  replaces  it 
with  a  cool  one,  and  the  rate  of  transmission  increases  approximately 


EFFICIENCY  OF   THE  HEATING  SURFACE.  331 

as  the  square  of  the  difference  of  temperature  on  the  inside  and  out- 
side of  the  coil.  The  case  is  entirely  different  with  steam-boilers. 
There  is  in  all  modern  forms  of  boilers  a  rapidity  of  circulation  suf- 
ficient to  keep  all  the  water  surrounding  the  heating  surfaces  at 
nearly  the  same  temperature  of  the  steam,  so  that  the  difference  of 
temperature  on  the  two  sides  of  a  square  foot  of  heating  surface,  with 
uniform  furnace  conditions,  remains  practically  constant. 

If  there  should  be  a  film  of  steam,  or  a  "steam-pocket,"  on  one 
side  of  the  surface,  keeping  the  water  from  wetting  it,  the  transmis- 
sion of  heat  would  be  greatly  diminished,  so  that  there  might  even 
be  danger  of  the  plate  becoming  overheated;  but  this  condition  is 
unlikely  to  happen  in  boilers  of  any  of  the  ordinary  forms. 

Upon  this  subject  Charles  Whiting  Baker  writes  as  follows:* 

So  far  as  the  transmission  of  heat  upon  the  boiler  in  making  steam 
is  concerned,  the  circulation  of  the  water  in  boilers  is  of  a  good  deal 
less  consequence  than  has  sometimes  been  claimed.  I  do  not  mean 
by  this  that  it  is  not  worth  while  to  make  proper  provision  for  circu- 
lation. There  are  possibly  some  boilers  worked  with  forced  draft, 
such  as  the  tube-plates  of  marine  boilers,  where  it  is  so  difficult  for 
the  steam-bubbles  to  get  away  fast  enough  that  we  have  a  mass  of 
foam  instead  of  water  in  contact  with  the  plate.  Under  such  condi- 
tions, of  course,  the  plate  is  bound  to  be  heated;  but  I  know  of  no 
evidence  that  this  is  any  other  than  a  rare  occurrence,  even  in  boilers 
which  are  pushed  most  severely.  .  .  .  Let  it  be  understood  that  I 
am  referring  to  circulation  only  as  affecting  the  transfer  of  heat  and 
the  consequent  economy  and  capacity  of  the  boiler.  Good  circulation 
is  desirable  to  prevent  unequal  heating  of  the  boiler  and  consequent 
straining,  and  it  may  be  desirable  in  preventing  deposits  of  scale  and 
mud  in  places  where  they  are  least  desirable;  but  that  it  has  any 
appreciable  effect  on  economy  and  capacity  is  not  proved  and  prob- 
ably cannot  be. 

Dr.  Charles  E.  Emery  in  a  discussion  on  "Tubulous  Boilers/' 
says:f 

Our  original  conception  of  "convection"  or  "circulation"  is  ex- 
emplified in  all  boilers  of  ordinary  type.  Multiplication  and  various 
arrangements  of  the  tubes  make  this  circulation  more  and  more  active 
without  changing  its  nature  until,  with  the  very  small  tubes  referred 
to  by  Mr.  Thornycroft,  the  action  becomes  violent  and  somewhat  in- 
termittent, like  a  geyser. 

*  Trans.  A.  S.  M.  E.,  vol.  xix,  p.  579. 

t  Journal  Am.  Soc.  of  Naval  Engineers,  vol.  ii.  No.  3. 


332  STEAM-BOILER  ECONOMY. 

We  then  have  this  progression:  a  boiler  in  which  the  circulation 
is  like  that  in  a  kettle,  with  steam  and  water  rising  at  the  centre  and 
water  descending  at  the  sides,  will  operate  satisfactorily;  so,  also, 
special  and  sectional  boilers  provided  with  water  up-takes  and  down- 
takes,  from  the  heating  surface  to  a  separate  drum,  will  circulate  on 
the  same  principles  and  operate  satisfactorily.  Curiously,  this  will  be 
the  case  whether  the  up-takes  be  large  or  considerably  contracted. 
We  know  that  vertical  boilers  will  operate  well  when  there  is  a  large 
space  around  the  tubes  for  circulation;  but  the  naval  launch  boilers 
and  Mr.  Manning's  modification  of  the  same,  where  the  shell  is 
brought  in  close  to  the  tubes  till  it  acts  like  a  corset  to  prevent  free 
circulation,  also  operates  well.  So,  also,  a  locomotive  boiler,  with 
plenty  of  room  around  the  tubes,  operates  well,  and  it  also  operates 
well  when  there  is  very  little  room  around  the  tubes;  the  fact  being 
that,  with  a  large  area  of  down-take,  a  large  quantity  of  water  is 
moved  at  a  slow  velocity,  while  with  less  area  a  less  quantity  of  water 
is  moved,  but  at  a  higher  velocity,  produced  by  a  greater  head,  due  to 
the  fact  that  less  water  is  mixed  with  the  steam  during  its  upward 
movement  and  the  density  of  the  column  is  less.  The  extreme  of  this 
progression  is  a  tube  so  long  and  narrow  that,  with  solid  water  fed 
into  the  bottom,  the.  greater  part  of  the  tube  will  be  a  mass  of  foam, 
and  mixed  steam  and  water  be  discharged  continuously  or  spasmodi- 
cally at  the  upper  end.  It  is,  moreover,  found  that  the  steam  and 
water  of  which  the  foam  is  composed  can  be  separated  in  smaller 
space  than  is  required  with  less  vigorous  ebullition.  In  other  words, 
contrary  to  our  old  ideas  of  large  steam-space,  large  disengaging  sur- 
face and  quiet  ebullition  to  prevent  foaming,  we  can  apparently 
obtain  as  good  results  in  a  boiler  composed  of  long,  narrow  tubes, 
each  of  which  foams  vigorously,  perhaps  spasmodically,  in  true  geyser 
style,  though  not  foaming  in  the  sense  ordinarily  understood  where 
water  is  carried  to  the  engine. 

In  ordinary  boilers  the  steam  passes  upward  and  bubbles  through 
the  water  at  the  disengaging  surface,  which  plan  operates  satisfac- 
torily, but  with  the  geyser  type  of  boilers  there  are  differences  of 
opinion  whether  or  not  it  is  best  to  discharge  the  upward  current  of 
mixed  steam  and  water  under  the  surface  of  the  water  in  the  drum 
or  entirely  above  it.  Mr.  Thornycroft  advocates  the  latter,  and  this 
system  is  adopted  with  modifications  in  the  Ward  and  Belleville 
boilers. 

A  gentleman  discussing  Mr.  Thornycroft's  paper  claims,  how- 
ever, that  it  is  better  to  discharge  the  water  and  steam  from  small 
tubes  below  the  water-level  in  the  separating-drum.  It  may  still  be 
considered  doubtful  which  system  will  carry  least  water  to  the  steam- 
pipe.  In  the  end -it  will  probably  be  found  that  each  mode  of  opera- 
tion is  adapted  to  a  particular  set  of  conditions. 

Efficiency  does  not  Depend  on  the  Type  of  Boiler. — It  will  be 
shown  in  the  chapter  on  Eesults  of  Trials  of  Steam-boilers  that  boilers 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


333 


of  a  great  variety  of  types  have  all  given  practically  identical  economic 
results,  approaching  the  maximum  possible  results  when  the  operat- 
ing conditions  are  favorable,  but  the  following  extract  from  the  same 
discussion  of  Dr.  Emery,  quoted  above,  may  be  given  here: 

The  economy  of  a  boiler  does  not  depend  upon  its  type,  or  the 
particular  way  the  water  is  circulated,  but  upon  the  simple  prin- 
ciple that  when  there  is  proper  circulation  of  both  the  water  and  the 
products  of  combustion,  the  economic  result  is  a  function  of  the 
average  quantity  of  combustible  burned  per  square  foot  of  heating  sur- 
face. It  is  important  that  there  be  proper  circulation,  not  only  of 
the  water,  but  of  the  products  of  combustion.  Many  special  boilers 
have  large  chambers  and  curious-shaped  passages,  so  arranged  that 
the  products  of  combustion  do  not  necessarily  pass  over  all  portions 
of  the  heating  surface ;  the  current  takes  the  lines  of  least  resistance, 
and  while  the  surface  actually  passed  over  is  very  efficient,  the  average 
efficiency  is  low. 

It  being  settled  that  the  economy  of  the  different  types  of  boiler  is 
based  on  the  same  law,  the  efficiency  is  frequently  very  low,  which  is 
due  generally  to  the  improper  distribution  of  the  heated  gases  over 
the  heating  surfaces,  whereby  a  large  portion  of  the  gases  can  take  a 
short  circuit  to  the  stack.  This  difficulty  is  easily  overcome  in  ordi- 
nary boilers  by  reducing  the  cross-area  for  draft,  so  that  the  whole 
heating  surface  becomes  efficient,  which  can  be  done  if  the  products 
of  combustion  either  pass  through  fire-tubes  or  between  water-tubes. 
With  tubulous  boilers  it  is  more  difficult,  as  all  possibility  of  direct 
access  must  be  given  up  if  the  tubes  are  massed  closely  together  in  a 
flue.  In  the  writer's  opinion,  the  best  form  of  boiler  for  reasonable 
rates  of  combustion  is  one  with  inclined  tubes  connected  by  up-takes 
and  down-takes  to  a  chamber  or  drum  above,  as  in  many  sectional 
boilers. 

Comparison  of  Lancashire  and  Multitubular  Boilers. — Chas. 
Erith,  in  Engineering,  Feb.  4,  1913,  gives  the  following  dimensions 
of  a  Lancashire  and  of  a  horizontal  return  tubular  boiler,  each  of 
which,  he  says,  is  equally  capable  of  the  rating  of  300  American 
boiler  horsepower  or  10,350  Ibs.  hourly  equivalent  evaporation  from 
and  at  212°  F. 


Shell 
Dimensions. 

Heating 
Surface. 

Gas  Flues,  Number 
and  Size. 

Furnace 
Width. 

Multitubular.  .  .  . 
Lancashire  

20X7  ft. 
30X8  ft. 

3056  sq.ft. 
1000 

192,  3  in.  X  20  ft. 
2,  39  in.  X  30  ft. 

7  ft,  1  in. 
6  ft.  1  in. 

"With  correct  combustion  and  good  coal,"  says  Mr.  Erith,  "either 
boiler  should  give  say  72%  efficiency  without,  or  say  78%  with,  an 
economizer."  His  conclusion  is  that  the  Lancashire  boiler  with  only 


334  STEAM-BOILER  ECONOMY. 

1000  sq.  ft.  heating  surface,  is  the  equal,  both  in  capacity  and 
efficiency,  of  a  multitubular  boiler  of  3056  sq.  ft.  heating  surface. 
The  fact  is  that  with  good  coal  and  "correct  combustion"  (that  is 
combustion  in  a  fire  brick  chamber  and  with  the  air  supply  controlled 
by  gas  analysis)  and  proper  protection  against  air  leaks  and  radia- 
tion, the  multitubular  boiler  could  be  driven  to  2%  times  its  rating, 
or  750  H.P.  without  the  efficiency  falling  below  72%.  It  would 
then  be  driven  at  the  rate  of  (750X34.5) -7-3056=8.47  Ibs.  from  and 
at  212°  per  sq.  ft.  of  heating  surface,  as  compared  with  10.35  Ibs.  for 
the  Lancashire  when  operating  at  only  300  H.P.  There  is  no 
reason  to  believe  that  a  square  foot  of  surface  of  the  multitubula-r 
boiler  is  any  less  efficient  in  transmission  of  heat  than  a  square  foot 
of  Lancashire  boiler,  while  the  latter  has  the  disadvantage  of  greatly 
increased  radiating  surface,  greater  cost  of  boiler  and  setting  and  of 
space  occupied,  and  narrower  furnace  width.  These  reasons  have 
prevented  the  introduction  of  the  Lancashire  boiler  in  the  United 
States,  and  will  in  time  no  doubt  cause  its  disappearance  in  England. 

It  is  interesting  to  note  that  the  total  area  of  the  two  39-in. 
gas  flues  of  the  Lancashire  boiler  is  16.6  sq.  ft.  while  that  of  the  192 
tubes  of  the  multitubular  boiler  is  only  8.1  sq.  ft.  If  both  boilers 
were  driven  at  the  same  rate,  using  the  same  amount  of  coal  and  the 
same  air  supply  the  velocity  of  the  gases  in  the  tubular  boiler 
would  be  more  than  double  the  velocity  in  the  Lancashire,  and 
if  the  American  boiler  were  driven  to  750  H.P.  the  velocity 
would  be  more  than  five  times  as  great.  The  fact  that  the  two  boilers 
give  about  the  same  efficiency  is  strong  indication  that,  contrary  to 
the  opinions  of  some  recent  writers,  the  velocity  of  the  gases  has 
little  if  anything  to  do  with  boiler  efficiency. 

Effect  of  Velocity  of  Gases  on  Efficiency. — The  velocity  of  the 
gases  varies  not  only  with  the  weight  of  coal  burned  and  inversely 
as  the  area  of  the  gas  passage,  but  also  with  the  weight  of  gas  per 
pound  of  coal  and  with  the  volume  in  cubic  feet  per  pound  of  gas, 
which  varies  with  the  temperature  from  the  fire-box  to  the  chimney 
flue.  To  eliminate  some  of  these  variables  let  us  assume  that  the 
weight  of  gas  is  20  Ibs.  per  Ib.  of  coal  burned  and  that  the  velocity 
is  measured  at  a  point  in  the  gas  passage  where  the  temperature  is 
about  1000°  F.  and  where  its  volume  is  36  cu.  ft.  per  Ib.  Then 
20X36-^-3600  =  0.2  cu.  ft.  of  gas  per  second  per  pound  of  coal  burned 
per  hour.  If  F=  Ibs.  coal  per  hour  and  A=  area  of  gas  passage  in 
sq.  ft.  then  0.2F/A  —  velocity  of  the  gas  in  feet  per  second,  which 
gives  us  a  rough  approximation  by  which  we  may  estimate  the 
relative  velocity  of  the  gases  in  different  boilers.  For  the  purpose 
of  comparison  we  may  take  the  Lancashire  and  multitubular  boilers 
above  referred  to,  the  former  evaporating  10,350  and  the  latter 
750X34.5  =  25,875  Ibs.  water  from  and  at  212°  per  hour,  and  each 
evaporating  10  Ibs.  water  per  Ib.  of  coal.  We  may  also  take  the  Galloway 
(a  modified  Lancashire)  boiler  tested  at  the  Centennial  Exhibition 
in  1876  for  maximum  economy  with  semi-bituminous  coal,  and  two 


EFFICIENCY  OF   THE  HEATING  SURFACE. 


335 


tests  of  a  locomotive  reported  by  Prof.  W.  F.  M.  Goss,  in  Bulletin 
402  of  the  U.  S.  Geological  Survey,  1909,  in  .the  latter  case  using 
combustible  instead  of  coal  burned,  on  account  of  the  loss  of  cinders 
in  the  smoke-box  and  stack.  The  data  are  as  follows : 


Equivalent. 

Boiler. 

H.P. 

Developed. 

Fuel  Burned 
perHr.,    * 
Lbs. 

Area  of  Gas 
Passage, 
Sq.ft. 

Velocity  of 
Gas,  Ft. 
per  Sec. 

Efficiency. 

Evapora- 
tion 
per  Sq.ft. 
H.S.  per 

Hr.,  Lba. 

Galloway  

103 

284 

11.9 

4.8 

74.5 

3.20 

Lancashire.  .  .  . 

300 

1035 

16.6 

12.5 

72 

10.35 

Multitubular.  . 

750 

•  2588 

8.1 

64 

72 

8.47 

Locomotive  .  .  . 

181 

504 

3.4 

28 

74.1 

5.12 

i  i 

469 

1569 

3.4 

92 

62.7 

13.30 

The  first  of  the  two  locomotive  tests  and  the  test  of  the  Galloway 
boiler  both  show  high  efficiency  for  hand  firing,  but  in  the  former  the 
velocity  of  gases  is  5.8  times  that  in  the  latter.  The  second  of 
the  locomotive  tests  shows  a  velocity  of  gas  19  times  that  in  the 
Galloway  boiler,  but  the  efficiency  was  low,  on  account  of  the  high 
rate  of  driving,  and.  probably  also  on  account  of  imperfect  combus- 
tion,, as  the  unaccounted  for  loss  in  the  heat  balance  was  10.6  per 
cent.  It  will  be  difficult  to  derive  from  the  figures  in  the  above 
table  any  confirmation  of  the  belief  that  velocity  of  the  gases  is  an 
important  factor  of  efficiency. 


APPENDIX  TO  CHAPTER  IX. 

NOTE  1,  p.  288. — The  integration  may  be  done  as  follows : 
Let  (T  -  0  =  x,  d(T  -  t)  =  dT  =  dx,  t  being  a  constant. 


dT 


(T  - 


rTi 

;  ( 

JT, 


S 
acw 


T2  -t       Tl  -t' 


After  finding  this  formula  Eankine  proceeds  as  follows  ("Steam- 
engine,"  p.  265)  : 


Efficiency  = 


TI    ~ 


S(Tl  -  t) 


-  t 


S(Ti  -  t)   +  cwa 


Let  H  =  expenditure  of  heat  in  raising  the  temperature  of  the  hot 
gas  above  that  of  the  water.     Then  TI  —  t  =  H  -i-  cw,  whence 


SH/cw 


S 


-  t 


SH/cw  +  acw      S+  ac2w2/H' 


336  STEAM-BOILER  ECONOMY. 


Again,  p.  293,  Rankine  says: 

"Let  E  =  theoretical  evaporative  power  and  E\  =  available 
evaporative  power  of  1  lb..  fuel,  in  a  boiler  in  which  the  area  of  heat- 
ing surface  is  S.  Then 

77T  Ci 

^-=B.       s 


E  S+  ac2w2/H' 

where  B  is  a  fractional  multiplier  to  allow  for  various  losses  of  heat, 
whose  value  is  to  be  found  by  experiment.  Now  c2  w2  is  proportional 
to  F2  V02,  where  F  =  Ibs.  of  fuel  burned  in  the  furnace  in  a  given 
time,,  and  F0  is  the  volume  at  32°  of  the  air  supplied  per  lb.  of  fuel. 
Also  H  oc  F  X  a  constant.  Hence  it  may  be  expected  that  the 
efficiency  of  a  furnace  will  be  expressed  to  an  approximate  degree  of 
accuracy  by 

EI  BS 

E     "  S  +  AF* 

where  A  is  a  constant  to  be  found  empirically,  and  is  probably  pro- 
portional approximately  to  the  square  of  the  quantity  of  air  per  lb. 
of  fuel/' 

This  is  Rankine's  formula  for  efficiency  as  a  function  of  the  heat- 
ing surface,  which  is  often  quoted,  but  it  is  not  generally  known  that 

ET  rri       _    rp 

his  so-called  "  efficiency,"  -=r  =—&  --  T,  is  quite  different  from  the 

Ci  1  I    —    t 

Ei  /  rp       _    rp 

efficiency  as  defined  by  Hale  and  others,  viz.,  —  -  =     1    —  -,    which 

hiv  T\ 

corresponds  to  what  is  commonly  known  as  "the  efficiency  of  a 
boiler."  Suppose  in  a  given  case  TI  =  2400,  T2  =  600,  t  =  300.  Then 

Ea  -/I    —    -/  2          1800          Mf  /v>    •  i   -I      T-»       i  •        »     j 

=  ^T^.  =  75  per  cent  efficiency,  while  Rankine  s  for- 


iLp  1 

mula  would  give  1800  -=-  2100  =  85.7  per  cent.     The  coefficients  A 
and  B  are  given  by  Rankine  as  follows  : 

B        A 

Boiler  Class  I.    The  convection  taking  place  in  the  best  manner,  either 
by  introducing  the  water  at  the  coolest  part  of  the  boiler  and  mak- 
ing it  travel  gradually  to  the  hottest,  or  by  heating  the  feed-water 
in  a  set  of  tubes  in  the  up-take;  the  draft  produced  by  a  chimney  1         0.5 
Boiler  Class    II.    Ordinary  convection,  chimney  draft  ..............     -H     0.5 

Boiler  Class  III.    Best  convection,  forced  draft  ....................    1         0.3 

Boiler  Class  IV.    Ordinary  convection,  forced  draft  ................     M     0.3 

No  satisfactory  reason  is  given  for  the  adoption  of  these  values. 
These  coefficients  of  Rankine  are  quite  different  from  the  A  and  B  of 
the  formulae  (8)  and  (9)  on  page  289. 

"True  Efficiency."—  In  the  reports  of  the  tests  of  the  U.  S. 
Geological  Survey  at  St.  Louis  in  1904  (see  Bulletin  325,  U.  S.  G.  S., 
1907,  also  Bulletin  18  of  the  U.  S.  Bureau  of  Mines,  1912)  the  term 


EFFICIENCY  OF  THE  HEATING  SURFACE.  337 

"true  efficiency"  is  used  to  denote  the  ratio  (Tx—  T2}-:-(Tf—  t),  in 
which  Tj  is  the  furnace  temperature,  T2  the  temperature  of  the 
chimney  gases  and  t  the  temperature  of  the  water  in  the  boiler.  The 
relation  of  this  ratio  to  that  of  the  one  commonly  accepted, 
(T1—T2)^-T1)  is  T1-7-(T1—  t},  which  is  a  constant,  independent 
of  Tz  whe.n  T1  and  t  are  constant.  The  introduction  of  this  new 
term  therefore  serves  no  useful  purpose.  For  a  detailed  criticism 
of  it  and  of  the  conclusions  of  the  writers  of  these  reports  concerning 
boiler  performance,  see  the  author's  article  on  Steam  Boiler  Ef- 
ficiencies in  Industrial  Engineering,  Oct.  1912,  p.  145. 
NOTE  2,  p.  288.  —  To  obtain  formula  (5)  we  have 

Eg'  _Tl-T2  _S_  T,-T2 

Ep  ~        Tl  cwa      (T2  -  ' 


T,Ea'  =  T,EP  -  T2EP-  T2  =  T,  (Ep  ~  Ea' 

uv 

Substituting  this  value  of  T2  in  (4), 

-  ' 


E 


CWa 


'      A       (^ 
/ 


TjEg' 


(Tt  -  t)2Ep  -  (T,  - 

Put  ~  =  P,  and  (Tl  -  0  =  T3. 
o 


Then      P  =          *~*;    (PTt  +  T9Ti)E.'  =  T<?E, 

i  l&a 

E^_  T3*  T32+  T,  _(T,  -t)*+  T, 

EP       PT±  +  T3T!  "   T3  +  P     "    „,        ...  acw 

(1  1  —  t)  -\  —g~ 

NOTE  3,  p.  289.  —  Is  the  rate  of  transmission  directly  proportional 
to  the  temperature  difference?  Equations  (3)  to  (16)  are  based  on  the 
hypothesis  (according  to  Rankine)  that  the  rate  of  transmission  q 

(T—t}2 

varies  as  the  square  of  (T—t),  or  that  q  =  -  --  —  ,  a  being  a  constant. 

a 

This  hypothesis  has  been  objected  to  by  some  writers,  who  hold  that 
the  transmission  varies  directly  as  the  temperature  difference  instead 

(T—t] 
of  as  the  square,  or  q  =  ^7  —  ^,  in  which  ~b  is  a  constant.    Let  us  test 

the  validity  of  this  formula. 


338  STEAM-BOILER  ECONOMY 

Referring  to  eq.  (3),  we  have 


Integrating, 


cio 

_S_ 
cwb 


\    T-f 
=  hyp.  log.  -i 


From  eq.  (1),  we  obtain 


&f?  /  rp         j. 

whence        j^  =  hyp.  log 


log.   h-^L\Tl-t 


JF' 


If  all  the  quantities  in  the  second  member  of  this  equation  are 
known,  b  can  be  found,  but  if  b  is  given  and  Eaf  is  required,  the 
latter  cannot  be  found  by  direct  algebraic  process. 

Referring  to  the  diagram  Fig.  77,  page  299,  the  line  corresponding 
to/ =  20,  £=300,  72=0.1  corresponds  nearly  to  the  actual  maximum 
results  obtained  in  good  boiler  practice,  and  it  may  safely  be  assumed 
that  the  line  R  =  0  in  Fig.  78  closely  approximates  the  highest  possible 
results  with  /  =  20,  if  the  radiation  loss  were  entirely  suppressed. 
This  line  gives  us  values  for  Ea'/Ep  which  may  be  substituted  in  the 
above  formula,  in  order  to  obtain  the  value  of  b. 

From  the  table  on  page  297  we  find  that  with  K  =  14,800,  t  =  300, 
Ti  =  3083,  /  =  20,  c  =  0.24,  a  =  200,  K  =  0,  the  values  of  Ea'  and 
Ea/Ep  and  the  corresponding  values  of  b  are  as  follows: 


w 

1 

2 

3 

4 

6 

8 

S 

Ea'  = 

13.422 

13.077 

12.732 

12.387 

11.698 

11.008 

Ea'/Ep  = 

88.01 

85.74 

83.48 

81.22 

76.70 

72.18 

6  = 

0.759 

0.455 

0.340 

0.281 

0.214 

0.178 

1-5-6  = 

1.318 

2.198 

2.941 

3.589 

4.673 

5.618 

It  thus  appears  that  b  is  not  a  constant  but  a  variable,  varying  as 
some  decreasing  function  of  W'/S.  The  reciprocal  of  6,  or  1  -j-  b,  is 
also  a  decreasing  function  of  W/S.  We  therefore  conclude  that  the 
assumption  that  q  =  (T  —  t)  -f-  6,  or  that  the  rate  of  transmission 
varies  directly  as  the  difference  of  temperature,  is  incorrect. 


EFFICIENCY  OF   THE  HEATING  SURFACE.  339 

F.  Kingsley  (Eng.  Record,  Aug.  29,  1908)  discusses  at  length 
the  question  whether  the  rate  of  heat  transmission  varies  directly 
as  the  difference  of  temperatures  or  as  the  square  of  that  difference. 
He  shows  mathematically  that  if  the  transmission  varies  directly 
as  the  temperature  difference,  then  in  a  boiler  divided  into  four 
sections  of  equal  heating  surface  the  ratios  between  the  evaporation 
in  each  two  adjoining  sections  would  be  respectively  0.50,  0.50,  0.50; 
while  if  the  transmission  varies  as  the  square  of  the  temperature 
difference,  the  ratios  would  be  0.50,  0.60,  0.667.  He  calculates  these 
ratios  for  two  series  of  tests  used  by  M.  Havrez  (Proc.  Inst.  Civ. 
Engrs.,  vol.39)  to  demonstrate  that  the  heat  transfer  varied  directly 
as  the  temperature  difference,  and  three  series  of  tests  cited  by  Prof. 
Perry  in  his  book  on  steam  engines  to  substantiate  his  theory  based 
on  the  same  assumption.  The  average  figures  for  the  five  series 
of  tests  gives  for  the  three  successive  ratios  0.504,  0.589,  0.670, 
which  are  remarkably  close  to  the  figures  corresponding  to  the  as- 
sumption that  the  transmission  varies  as  the  square  of  the  tempera- 
ture difference. 

W 
NOTE  4,  p.  290.  —  Interpretation  of  formula  (7),  Ear  =  BEP—  A-~-. 

W 
—  If  —  =0.  Eaf  =  BE  p.     That  is,  the  evaporation  per  Ib.  of  fuel 

S 

will  be  the  greatest  when  the  evaporation  per  sq.  ft.  of  heating  surface 
is  least.     (This  will  not  be  true  when  radiation  is  considered.) 

If  A^-=BEP,  or  ^  =  ^  Ea'  =  0.    This  seems  to  be  a  paradox, 
o  o  A 

for  can  there  be  any  rate  of  evaporation  at  which  the  economy,  or  the 
evaporation  per  Ib.  of  fuel,  will  be  0?     Substituting  for  W  its  value 

4  F  'F  A  F  V  fl 

=  BE    -  ~^-'  and  for  Ea'  =  0BEP  *  " 


P 

o 

which,  if  BEp,  A,  and  S  are  finite  quantities,  can  only  be  true  if 
F  =  oo.  That  is,  when  W'/S  =  BEP/A,  a  finite  quantity,  the  fuel 
consumption  is  infinite,  and  any  actual  evaporation,  as  TF,  divided  by 
infinite  F  =  0. 

The  conclusion  is  that  a  rate  of  evaporation  per  sq.  ft.  of  heating 
surface  equivalent  to  W'/S  =  BEP/  A  can  never  be  reached  until  the 
fuel  consumption  F  is  so  great  that  the  final  temperature  of  the  gases 
T2  equals  their  initial  temperature  T19  which  can  occur  only  with  no 
transmission  of  heat  through  the  heating  surface,  or  with  an  infinite 
fuel  consumption. 

NOTE  5,  p.  291.  —  Development  of  equation  (11). 


Ea+       Ea  =  BE 


-  4  (^  +  fl); 


340 


STEAM-BOILER  ECONOMY. 


BE^ 
RS 


TFF          1  + 


RS 
W 


W 


The  last  term  equals  A-~-;     therefore   E 


NOTE  6,  p.  303.  —  Variable  Specific  Heats.  —  From  a  table  of  the 
thermal  capacity  of  various  gases  at  different  temperatures,  given  in 
Damour's  Industrial  Furnaces  (M.  E.  Pocket-book,  p.  537),  the  follow- 
ing figures  for  the  mean  specific  heat  (between  32°  F.  and  the  temper- 
atures named)  of  a  furnace  gas  consisting  of  12C02,  80,  SON  (cor- 
responding to  23  Ibs.  of  gas  per  Ib.  of  carbon),  have  been  computed: 


3000°  F. 

2800 

2600 

2400 

2200 


0.283 
0.279 
0.276 
0.273 
0.273 


2000°  F. 

1800 

1600 

1400 

1200 


0.266 
0.262 
0.258 
0.254 
0.251 


1000 c 
800 
600 
400 


F. 


0.249 
0.247 
0.246 
0.245 


Assuming  0.275  as  the  specific  heat  of  the  gas  in  a  furnace,  the 
computed  elevation  of  temperature  above  that  of  the  atmosphere, 
with  23  Ibs.  of  gas  per  Ib.  of  fuel,  and  a  heating  value  of  14,800 
B.T.U.  per  Ib.,  is  14,800-^(0.275  X  23)  =  2340°.  As  a  temperature 
of  3000°,  as  measured  by  pyrometers,  is  often  obtained  in  boiler 
furnaces,  it  is  probable  that  the  above  figures  for  specific  heats  at 
the  higher  temperatures  are  too  high. 

The  temperatures  T2  and  the  efficiencies  found  for  the  boiler  of 
20  sections  have  been  recalculated  on  the  basis  of  variable  specific 
heat,  with  /  =  20,  and  the  results  are  given  below,  compared  with 
those  found  in  the  original  computation  with  c  taken  at  0.24: 


Section  No 

1 

2 

3 

4 

5 

6 

7 

Value  of  C 

0.268 
1800 
2045 
32.61 
33.61 

0.257 
1456 
1571 
45.54 
49.00 

0.251 
1286 
1300 
53.80 
57.79 

0.250 
1120 
1125 
59.76 
63.47 

0.249 
1002 
1001 
64.01 
67.50 

0.248 
913 
910 
67.21 
70.46 

0.247 
844 
844 
69.69 
72.60 

Temperature  T-> 

Temperature  original 

Efficiency,  per  cent  

Efficiency,  original  

Section  No                   .    .        

8 

10 

12 

14 

16 

18 

20 

Temperature  T% 

789 
787 
71.66 
74.45 

714 
703 
74.63 
77.37 

653 
645 
76.79 
79.06 

608 
600 
78.40 
80.52 

573 
566 
79.64 
81.62 

545 
539 
80.63 
82.50 

522 
517 
81.44 
83.22 

Temperature  original 

Efficiency  per  cent 

Efficiency,  original  

The  difference  between  the  revised  and  the  original  results  are  not 
of  sufficient  importance  to  warrant  the  adoption  of  variable  specific 
heats  in  computations  of  boiler  efficiency,  especially  as  their  value 
at  the  different  temperatures  is  not  well  established. 


CHAPTER  X. 


TYPES  OF   STEAM-BOILERS. 

Evolution  of  Different  Forms  of  Boiler. — The  first  stage  in  the 
development  of  steam-boiler  construction  beyond  the  plain  cylinder 
boiler  was  the  recognition  of  the  fact  that  it  is  defective  in  providing 
too  little  heating  surface  for  its  first  cost,  for  the  ground  space  it 
occupies,  and  for  the  expense  of  its  setting.  Only  about  one-half  of 
its  whole  shell  surface  is  available  as  heating  surface;  the  remainder 
serves  only  to  hold  the  steam.  Increase  of  its  diameter  involves  in- 
crease of  the  thickness  of  its  shell,  and  hence  greater  cost  per  square 
foot  of  heating  surface,  as  well  as  increase  of  area  occupied.  Increase 
of  its  length  involves  equal  increase  of  ground  space  and  of  cost  of 


H    H    H    H    H    H    H 


h- 1    I— I    I— I    i-J 


FIG.  87. — DOUBLE-CYLINDER  BOILER. 

setting,  besides  increasing  the  difficulty  of  suspending  it  in  such  a 
manner  as  to  avoid  dangerous  strains.  Some  radical  change  of  form 
must  then  be  found.  In  the  United  States  the  first  departure  from 
the  plain  cylinder  boiler  was  made  in  two  different  directions  in  dif- 
ferent localities.  In  blast-furnaces  additional  heating  surface  was 
provided  by  hanging  one  cylindrical  shell  below  another,  joining  the 
two  by  short  legs.  Such  a  construction  is  shown  in  Fig.  87.  The 
upper  cylinder  was  generally  made  of  larger  diameter  than  the  lower. 
On  the  Ohio  and  Mississippi  rivers,  steamboat  boilers  were  made  by 
enlarging  the  diameter  of  the  cylinder  and  by  putting  two  flues  inside 
of  it,  the  gases  passing  under  the  boiler  and  then  returning  through 
the  two  flues  to  the  chimney,  which  was  placed  at  the  front  of  the 
boiler.  This  form  is  shown  in  Fig.  88.  This  boiler  came  into  univer- 
sal use  on  the  western  rivers,  and  into  quite  general  use  in  the  cities 
and  towns  located  along  these  rivers.  Until  about  the  year  1880  scarcely 

341 


342 


STEAM-BOILER  ECONOMY. 


any  other  kind  of  boiler  was  in  use  in  the  large  iron-mills  and  in  the 
mines  in  and  around  Pittsburg,  such  is  the  force  of  local  custom  and 
prejudice.  Now,  however,  it  is  rapidly  being  displaced  on  land  by 


FIG.  88. — TWO-FLUE  BOILER. 

modern  water-tube   boilers,   although  it   still  holds   its   own   on  the 
steamboats. 

Evolution  of  the  Steam-boiler  in  France  and  England. — In  France 
the  development  from  the  plain  cylinder  boiler  took  a  form  similar 


FIG.  89. — THE  "  ELEPHANT  "  BOILER. 


to  that  of  the  double-cylinder  boiler,  but  with  two  lower  cylinders 
hanging  from  the  upper  one,  as  shown  in  Fig.  89.  This  boiler  is 
commonly  called  the  "elephant"  boiler. 

In  England  the  plain  cylinder  boiler  developed  into  the  Cornish 
boiler,  in  which  the  cylinder  is  made  of  larger  diameter  and  a  large 


FIG.  90. — THE  CORNISH  BOILER. 

central  flue  is  built  into  it,  in  one  end  of  which  the  grate  is  placed. 
This  boiler  is  shown  in  Fig.  90.  A  modification  of  the  Cornish 
boiler  is  the  Lancashire,  containing  two  internal  furnaces  and  flues, 
shown  in  Fig.  91.  Another  modification  is  the  Galloway  boiler,  in 
which  the  two  internal  furnaces  lead  into  one  large  flue,  oblong  in 
cross-section,  crossed  by  a  number  of  conical-shaped  water-tubes, 


TYPES  OF  STEAM-BOILERS. 


343 


which  circulate  the  water  from  the  space  below  to  the  space  above 
the  flue,  baffle  the  course  of  the  gases  through  the  flue,  and  provide 
increased  heating  surface,  as  is  shown  in  Fig.  92.  The  Lancashire 
boiler  is  now  often  built  with  Galloway  tubes  crossing  each  of  its 


FIG.  91. — THE  LANCASHIRE  BOILER. 


FIG.  92.— THE  GALLOWAY 
BOILER. 


flues,  as  shown  in  Fig.  93.  This  cut  also  shows,  in  cross-section, 
the  common  form  of  setting  of  Galloway  and  Lancashire  boilers. 
The  gases  first  pass  through  the  internal  flues,  then  return  in  the 
two  external  flues  along  each  side,  and  finally  pass  through  the 


FIG.  93. — LANCASHIRE  BOILER  WITH  GALLOWAY  TUBES. 

single  flue  under  the  shell  of  the  boiler.  Sometimes  the  gases  are 
made  to  pass  to  the  front  under  one  side  of  the  shell  and  then  return 
to  the  rear  under  the  other  side.  All  of  the  boilers  above  described 
are  open,  although  to  a  smaller  degree,  to  the  same  objection  that 
has  been  raised  against  the  plain  cylinder  boiler — that  of  providing 
too  small  an  amount  of  heating  surface  for  their  cost  and  for  the 
ground  space  occupied.  The  objection  applies  less  to  the  Galloway 
than  to  the  other  forms. 


344 


STEAM-BOILER  ECONOMY. 


The  Horizontal  Return  Tubular  Boiler, — The  American  two-flue 
externally  fired  boiler  has  developed  through  the  stages  of  five  and  ten 


1 


FIG.  94. — HORIZONTAL  RETURN  TUBULAR  BOILER. 


FIG.  95. — RETURN  TUBULAR  BOILER  WITH  SETTING. 

flues  into  the  modern  American  horizontal  multitubular  externally 
fired  fire-tube  boiler,  containing  often  100  tubes  or  more,  of  3  or  4 
inches  diameter,  shown  in  Figs.  94  and  95. 


TYPES  OF  STEAM-BOILERS.  345 

Fig.  94  shows  the  most  recent  form  of  this  boiler  with  butt  and 
strap  riveting  on  the  longitudinal  seams,  adapted  for  high  pressures. 
Fig.  95  shows  an  earlier  form  for  moderate  pressures,  with  the 
common  style  of  setting.  The  steam-drum  shown  on  this  boiler  is 
now  generally  abandoned,  being  considered  a  useless  and  even  dan- 
gerous appendage. 

In  the  return  tubular  boiler  the  objection  of  insufficient  heating 
surface  in  proportion  to  space  occupied,  is  removed  to  a  greater  extent 
than  in  any  other  boiler  with  the  exception  of  some  forms  of  water- 
tube  boilers,  and  in  regard  to  cost  it  is  about  the  .cheapest  of  all 
boilers  for  a  given  extent  of  heating  surface.  It  is  probably  in  more 
general  use  in  the  United  States  than  any  other  form  of  boiler.  As 
already  stated,  it  is  practically  not  used  at  all  in  England,  where 
there  is  a  strong  prejudice  against  it  and  in  favor  of  the  internally 
fired  Lancashire  and  Galloway  boilers.  Its  extensive  introduction 
into  this  country  is  no  doubt  due  to  its  low  first  cost.  When  well 
made  of  good  material,  when  the  water  used  is  reasonably  free  from 
scale-forming  substances,  and  when  it  is  carefully  handled  and  fre- 
quently inspected,  it  may  give  satisfaction  for  long  periods  of  time, 
and  so  justify  the  favor  in  which  it  is  held.  This  type  of  boiler  is, 
however,  very  liable  to  explosion,  and  many  lives  are  lost  by  its  use 
every  year.  The  shell  of  the  horizontal  tubular  boiler  being  directly 
exposed  to  the  fire,  it  is  especially  liable  to  be  burned  or  weakened 
when  there  are  deposits  of  scale  or  grease  upon  it.  The  circular 
rivet-seams,  and  the  double  thickness  of  plates  at  the  seams  being 
exposed  to  the  fire,  are  also  elements  of  weakness. 

As  to  economy  of  fuel,  the  horizontal  tubular  boiler  is  subject  to 
the  same  rules  as  all  other  boilers.  Maximum  economy  may  be  ob- 
tained from  it  if  the  furnace  is  of  a  kind  which  will  burn  the  coal 
thoroughly,  if  the  extent  of  heating  surface  is  sufficient  for  the 
amount  of  coal  burned,  and  if  the  passages  through  the  flues  are  so 
restricted  in  area  that  the.  gases  traverse  the  upper  and  lower  rows 
with  approximately  the  same  velocity.  It  is  in  this  latter  condition 
that  the  horizontal  tubular  boiler  is  usually  defective.  There  is  a 
tendency  of  the  hot  gases  to  pass  through  the  upper  rows  of  tubes 
instead  of  through  all  the  tubes  alike.  This  is  easily  proved  by  in- 
serting a  stick  of  wood,  say  1  X'2  X  10  inches,  set  edgewise,  in  the 
end  of  each  tube  in  a  vertical  row,  nearest  the  chimney,  and  leaving 
it  there  for  say  half  an  hour.  The  sticks  in  the  upper  tubes  will 
usually  be  found  to  be  burned  up,  while  those  in  the  lower  tubes  will 


346 


STEAM-BOILER  ECONOMY. 


be  only  charred.  This  short-circuiting  of  the  gases  may  be  avoided 
by  partially  restricting  the  flow  through  the  upper  tubes,  but  it  would 
require  considerable  experimenting,  by  placing  thermometers  in  several 
of  the  tubes,  and  varying  the  relative  obstruction  to  the  current  in 
the  different  tubes  until  all  of  the  thermometers  showed  the  same 
temperature.  Actual  tests  of  tubular  boilers  show  results  varying  all 
the  way  from  about  11^  Ibs.  of  water  from  and  at  212°  per  Ib.  of 
combustible,  down  to  8  pounds,  or  about  30  per  cent,  with  no  differ- 
ence in  the  coal,  the  rate  of  combustion  or  the  character  of  the  firing 
to  explain  the  variation.  It  is  probable  that  in  such  cases  some  of  the 
low  figures  are  due  to  short  circuiting  of  the  gases,  which  might  be 
avoided  by  properly  retarding  the  flow  through  the  upper  tubes. 

The  Vertical  Tubular  Boiler. — If  a  horizontal  tubular  boiler  is 
filled  with  tubes,  turned  up  on  end  and  set  over  a  furnace,  it  becomes 


~ 


FIG.  96. — VERTICAL  TUBULAR 
BOILER. 


FIG.  97. — VERTICAL  BOILER  WITH 
SUBMERGED  TUBES. 


a  vertical  fire-tube  boiler.  It  is  more  common,  however,  to  build  this 
type  of  boiler  with  an  internal  fire-box  from  2  to  4  ft.  in  height.  The 
annular  space,  2  or  3  in.  wide,  between  the  fire-box  and  the  shell,  is 
known  as  the  water-leg.  The  roof  of  the  fire-box,  a  flat  sheet  into 
which  the  lower  ends  of  the  tubes  are  expanded,  is  called  the  crown- 
sheet,  and  the  flat  sheet  on  top  of  the  boiler  into  which  the  upper  ends 
of  the  tubes  are  expanded,  is  called  the  upper  tube-sheet.  The  ex- 
ternal appearance  of  such  a  boiler  is  shown  in  Figs.  96  and  97.  The 


TYPES  OF  STEAM-BOILERS.  347 

crown-sheet  is  just  below  the  hand-hole  plate  seen  in  the  front 
of  the  shell  some  distance  above  the  fire-door. 

This  boiler  is  the  most  commonly  used  type  of  boiler  in  the 
United  States  for  small  powers,  say  5  to  40  H.P.  It  is  also  the  most 
dangerous  form,  and  the  one  which  explodes  oftener  than  any  other. 
As  commonly  built,  the  water-level  is  carried  a  considerable  distance 
below  the  upper  ends  of  the  tubes,  which  are  therefore  apt  to  be  over- 
heated and  unduly  expanded,  bringing  severe  strains  on  both  the 
upper  tube-sheet  and  the  crown-sheet.  The  crown-sheet  is  apt  to 
accumulate  a  thick  layer  of  mud  and  scale,  which  is  liable  to  cause 
the  sheet  to  crack,  and  this  may  lead  to  an  explosion. 

Increased  safety  with  this  type  of  boiler  is  obtained  by  so  con- 
structing it  that  the  upper  ends  of  these  tubes  are  submerged,  and 
by  providing  facilities  for  inspection  and  for  the  removal  of  scale 
from  the  crown-sheet. 

The  vertical  tubular  boiler  is  usually  not  economical  of  fuel,  on 
account  of  its  being  designed  with  too  small  an  amount  of  heating 
surface  for  the  amount  of  coal  burned  in  its  fire-box,  but  it  may 
be  made  as  economical  as  any  other  boiler  if  properly  designed  and 
if  driven  at  not  too  high  a  rate.  The  fire-box  is  usually  too  low  to 
allow  of  complete  combustion  of  the  gases  distilled  from  soft  coal, 
even  semi-bituminous,  and  the  fire-tubes  are  too  short  to  absorb  the 
desired  amount  of  heat  from  the  hot  gases.  Eecent  designs  are  much 
better  in  these  respects.  Tubes  are  made  as  much  as  18  or  20  ft. 
long,  and  fire-boxes  as  high  as  8  ft.  from  the  grate-bars  to  the  crown- 
sheet  have  been  built,  with  good  results  as  to  economy  and  smoke- 
lessness  with  semi-bituminous  coal. 

The  Manning  Boiler,  Fig.  98,  is  a  modification  of  the  vertical 
tubular  boiler,  with  structural  features  peculiar  to  itself.  It  is  largely 
used  in  the  New  England  States.  An  especial  merit  claimed  for  it  is 
economy  of  ground  space.  A  boiler  which  has  given  180  boiler  horse- 
power is  set  on  a  space  8  ft.  in  diameter.  The  difference  in  expan- 
sion and  contraction  between  the  tubes  and  the  outer  shell  is  taken 
up  in  the  double-flanged  head  connecting  the  barrel  of  the  boiler 
with  the  outside  of  the  fire-box,  and  forming  an  expansion  joint.  By 
means  of  this  head  the  fire-box  is  enlarged  so  as  to  give  the  desired 
proportion  of  area  of  heating  surface  to  grate  surface.  The  crown 
is  of  such  height  to  form  a  large  combustion-chamber. 

The  outer  fire-box  shell  is  carried  well  up  above  the  head,  and 
hand-holes  are  placed  exactly  on  a  line  with  the  crown-sheet.  The 


348 


STEAM-BOILER  ECONOMY. 


tubes  are  placed  in  straight  rows, 
and  at  right  angles  to  one  another 
extend  two  cleaning-channels  of 
ample  size.  A  bent  tube  may 
therefore  be  inserted,  and  the 
crown-sheet  thoroughly  washed 
and  cleaned.  In  the  water-leg 
also  are  placed  a  number  of  hand- 
holes  and  a  cleaning  chain  by 
means  of  which  any  sediment 
that  may  accumulate  may  be 
stirred  up  and  removed. 

The  Locomotive  Boiler. — The 

peculiar  merits  of  the  ordinary 
form  of  locomotive  boiler,  as  used 
in  locomotives,  are  its  allowing 
to  be  crowded  into  a  limited  space 
a  great  extent  of  heating  surface, 
with  a  large  fire-box,  its  being 
self-contained,  requiring  no  ex- 
ternal furnace,  and  its  great 
strength,  admitting  of  working 
pressure  of  200  Ibs.  and  over.  To 
obtain  these  advantages  many 
other  things  have  to  be  sacrificed. 
It  is  .expensive,  difficult  to  clean 
and  to  repair,  is  not  durable,  and 
must  be  driven  with  forced  blast. 
It  is  also  not  economical  when 
driven  at  the  rate  required  for 
locomotive  practice,  the  gases, 
leaving  the  smoke-stack  at  higli 
temperatures,  and  at  rapid  rates 
of  combustion  a  considerable 
amount  of  unburned  coal  is  car- 
ried out  of  the  stack  or  into  the 
smoke-box. 

Nevertheless,  the  locomotive 
type  of  boiler  is  not  uncommon  in 
stationary  practice,  its  chief  field 


FIG.  98. — THE  MANNING  BOILER. 


TYPES  OF  STEAM-BOILERS.  349 

being  for  portable  and  semi-portable  boilers.     A  common  form  of 
the  type  as  used  for  stationary  service  is  shown  in  Fig.  99. 


k.*-i*'o"-.  vl 

c.1  U  —•*• 

FIG.  99. — LOCOMOTIVE  TYPE  OF  BOILER  FOR  STATIONARY  SERVICE.' 

The  "Scotch"  Marine  Boiler. — Boilers  for  marine  purposes  are 
built  in  a  great  variety  of  types,  including  modifications  of  the  exter- 
nally fired  horizontal  fire-tube  and  water-tube  boilers,  and  of  the 
various  forms  of  internally  fired  boilers,  such  as  the  vertical  tubular, 
the  locomotive,  the  Lancashire,  etc. 

Take  the  Lancashire  boiler,  Fig.  91,  with  its  cylindrical  shell  and 
two  internal  furnaces,  and  substitute  for  the  two  smoke-flues  a  com- 
bustion-chamber, a  tube-sheet,  and  a  great  number  of  small  tubes, 
and  we  have  the  first  stage  of  development -,  of  the  Lancashire  into  a 
modern  marine  boiler.  The  next  stage  is  to  increase  the  diameter  of 
the  boiler  and  shorten  its  length,  extending  the  combustion-chamber 
upwards  and  putting  the  nest  of  tubes  above  the  furnace-flues  instead 
of  in  their  rear,  causing  the  tubes  to  return  the  gases  toward  the  front 
of  the  boiler.  This  makes  what  is  known  as  the  "Scotch"  boiler,  so 
called  because  it  was  first  built  on  the  Clyde.  Increase  the  diameter 
to  14  or  15  ft.,  and  put  in  three  or  four  corrugated  furnaces,  and  we 
have  the  latest  form  of  the  boiler  shown  in  Fig.  100. 

This  boiler  is  often  made  "double-ended,"  that  is,  it  is  increased  in 
length  and  furnaces  are  placed  in  both  ends,  delivering  their  gases  into 
a  common  combustion-chamber  in  the  middle,  from  which  the  smoke- 
tubes  extend  to  the  chimney-flues  at  each  end. 

The  Scotch  boiler  is  now  in  almost  universal  use  in  large  ocean- 
going merchant  vessels,  but  in  most  large  ships  of  war  it  has  been 
displaced  by  the  water-tube  boiler. 

The  problem  of  designing  a  thoroughly  satsfactory  boiler  for 
ocean  service  is  one  of  great  difficulty,  and  at  best  it  offers  but  a  choice 
of  evils.  In  stationary  service,  on  land,  a  boiler  to  be  satisfactory 


350 


STEAM-BOILER  ECONOMY. 


must  have  abundant  grate  surface,  so  that  fires  do  not  need  to  be 
forced;'  a  large  combustion-chamber,  to  help  in  the  burning  of  the 
volatile  gases,  and  plenty  of  heating  surface  to  extract  the  heat  from 
the  gases.  In  marine  service  not  one  of  these  conditions  can  be  pro- 
vided, for  space  on  board  ship  is  too  valuable.  The  problem  may  be 
stated  thus :  in  a  fire-room  of  so  many  square  feet  area  and  so  many 
feet  high  construct  boilers  which  shall  have  the  greatest  number  of 
square  feet  of  grate  surface,  and  heating  surface  sufficient  to  absorb 
65  or  70  per  cent  of  the  heating  value  of  the  coal  when  the  coal  is 


FIG.  100. — THE  SCOTCH  MARINE  BOILER. 

burned  at  the  rate  of  50  Ibs.  per  hour  per  square  foot  of  grate;  at 
the  same  time  the  boiler  must  be  strong,  durable,  easily  cleaned  and 
repaired,  and  must  not  weigh  too  much  nor  carry  too  much  weight 
of  water. 

Until  within  recent  years  the  Scotch  boiler  has  been  the  one  which 
most  nearly  filled  these  difficult  requirements.  It  cannot  fill  them 
all,  for  it  is  heavy,  both  in  metal  and  in  water  carried,  is  costly  and 
difficult  to  repair. 

Reason  for  the   Survival   of  the  Scotch   Marine   Boiler.— Rear 

Admiral  G.  W.  Melville,  U.  S.  N.  says  (Eng'g  Magazine,  Jan.  1912)  : 
"It  seems  to  me  that  almost  the  only  reasons  for  the  continued  use 
of  the  cylindrical  boiler  are  the  fact  that  marine  people  are  so 


TYPES  OF  STEAM-BOILERS.  351 

thoroughly  familiar  with  it  and  that  nearly  every  shipyard  has  a 
boiler  plant  for  turning  out  such  boilers.  In  many  cases  the  design 
of  the  machinery  is  left  to  the  builders,  who  are  thoroughly  com- 
petent, but  who  naturally  prefer  to  install  a  boiler  which  will  give 
employment  to  the  plant  which  they  already  have.  This  is  easy  to 
understand.  What  I  cannot  understand,  however,  is  that  owners 
and  independent  designers  should  continue  to  install  such  an  un- 
necessary amount  of  dead  weight  when  it  might  be  replaced  by  lighter, 
safer,  and  more  efficient  boilers  leaving  a  considerable  increase  in 
the  cargo  carrying  capacity.  .  .  .  With  the  latest  and  best  types  of 
water-tube  boilers  we  are  able  to  secure  not  only  power  and  lightness, 
but  also  economy." 

The  Water-tube  Boiler. — In  the  water-tube  steam-boiler  the  heat- 
ing surface  consists  chiefly  of  tubes  of  small  diameter,  the  water  being 
contained  in  the  inside  of  the  tubes  while  the  flame  and  gases  of  com- 
bustion are  on  the  outside.  The  water-tube  type  of  boiler  forms  a 
class  broadly  distinguished  from  the  flue  or  tubular  boiler,  also  called 
the  fire-tube  boiler,  in  which  the  water  is  contained  in  a  large  exter- 
nal shell  and  the  gases  pass  through  the  flues  or  tubes.  It  is  by  no 
means  a  recent  invention,  since  boilers  of  this  type  were  made  over 
a  century  ago,  many  forms  of  them  being  shown  in  standard  treatises 
on  boilers.  It  is  only  since  the  year  1870,  however,  that  they  hav-e 
come  into  extensive  use. 

The  great  advantages  of  the  water-tube  type  over  all  other  forms 
of  boiler,  in  point  of  safety  from  destructive  explosions,  ability  to 
stand  the  highest  pressures,  perfection  of  circulation,  compactness, 
economy  of  fuel,  etc.,  were  well  understood  many  years  ago,  but  it 
required  a  long  course  of  development  and  experiment  to  discover 
what  arrangement  of  parts  and  what  mechanical  details  were  neces- 
sary to  combine  these  advantages  with  others  not  less  essential,  such 
as  durability,  and  facility  for  cleaning  and  repair. 

The  form  in  which  the  water-tube  boiler  is  now  commonly  made 
consists  of  a  bank  of  tubes,  usually  4  in.  in  diameter,  and  from  12  to 
18  ft.  long,  inclined  at  an  angle  of  about  15°  from  the  horizontal,  and 
surmounted  by  a  horizontal  water-  and  steam-drum,  .from  30  to  48  in. 
diameter,  of  about  the  same  length  as  the  tubes.  The  tubes  are  ex- 
panded into  boxes  or  "headers,"  at  each  end,  and  these  are  connected 
to  the  drum  overhead  by  circulating  tubes  or  other  connections.  The 
water-level  is  carried  about  the  middle  of  the  drum,  which  on  account 
of  its  comparatively  large  diameter  offers  a  large  disengaging  surface 
which  tends  to  insure  the  production  of  dry  steam.  The  furnace  be- 


352  STEAM-BOILER   ECONOMY. 

ing  placed  under  the  bank  of  tubes  (or  better,  when  soft  coal  is  used 
in  a  fire-brick  oven  built  in  front  of  the  boiler)  the  flame  circulates 
amongst  them,  being  properly  guided  by  suitable  passages  so  as  to  cause 
it  to  give  up  as  much  of  its  heat  as  possible  before  being  allowed  to 
escape  into  the  chimney. 

There  are  now  several  different  makes  of  these  boilers  in  the 
market,  to  all  of  which  the  above  description  will  apply.  They  differ, 
however,  in  proportions  of  parts,  in  mechanical  details,  especially  of 
the  headers  and  their  connection  to  the  drum,  in  furnaces,  in  ma- 
terial, and  in  workmanship.  The  boiler  type  itself  being  good  it  still 
requires  engineerng  skill  and  good  judgment  to  determine  what  size 
of  boiler,  what  kind  of  furnace,  and  what  arrangement  of  flues 
and  chimney  should  be  adopted  to  give  the  best  results,  consider- 
ing the  character  of  work  to  be  done,  and  the  kind  of  fuel  to  be 
used. 

The  great  success  of  the  water-tube  type  of  boiler  is  chiefly  shown 
by  the  fact  that  it  is  now  being  most  extensively  adopted  by  the  con- 
cerns which  use  the  largest  amount  of  power,  such  as  electric  light  and 
power  stations,  large  sugar  refineries,  iron  and  steel  works  and  the 
like,  which  require  thousands  of  horse-power  in  one  plant. 

Early  Forms  of  Water-tube  Boilers. — Fitch  &  Voight's  boiler, 
used  by  John  Fitch  in  his  steamboat  on  the  Delaware  River  in  1787; 


FIG.  101.— FITCH  &VOIGHT.  1787.  FIG.  102.— JOHN  STEVENS,  1803, 

Barlow's  boiler,  patented  in  France  in  1793,  and  used  by  Robert  Ful- 
ton in  his  steamboat  experiments  on  the  Seine,  in  France,  in  1803,  and 
John  Stevens's  boiler,  used  in  his  experimental  twin-screw  steam- 
boat on  the  Hudson  River  in  1804,  are  three  early  forms.  They  are  all 
described  in  Thurston's  "Growth  of  the  Steam  Engine."  Fitch's 
boiler  was  a  "pipe-boiler,"  consisting  of  a  small  water-pipe  winding 


TYPES  OF  STEAM-BOILERS.  353 

backward  and  forward  in  the  furnace,  and  terminating  at  one  end  at 
the  point  at  which  the  feed-water  was  introduced  and  at  the  other 
uniting  with  the  steam-pipe  leading  to  the  engine.  Barlow's  had  a 
nest  of  horizontal  tubes  connected  to  water-legs  at  both  ends.  Ste- 
vens's  had  slightly  inclined  tubes,  closed  at  one  end  and  connected  to 
a  water-chamber  at  the  other. 

Some  More  Recent  Forms. — The  following  notes,  with  accompany- 
ing illustrations,  are  taken  by  permission  from  "Facts/'  a  pamphlet 


FIG.  103.— JOLT,  1857. 

published  by  The  Babcock  &  Wilcox  Co.  in  1895.  They  show  a  few  of 
a  great  number  of  designs  of  water-tube  boilers  that  have  been  made 
by  varying  the  form  or  arrangement  of  four  elementary  units,  viz. : 


FIG.  104. — FIELD,  1866. 

1,  a  tube  closed  at  one  end ;  2,  a  bent  tube ;  3,  an  aggregation  of  pipes 
and  fittings ;  4,  a  group  of  straight  tubes  connected  with  water-cham- 
bers at  each  end. 

BOILERS  WITH   CLOSED-END  TUBES. 

Joly,  1857. — A  sectional  boiler  with  vertical  drop-tubes,  each  fed 
by  an  internal  tube  extending  nearly  to  the  bottom. 

Field,  1866. — A  cylinder  boiler  with  radiating  drop-tubes  fitted  to 
the  lower  side.  Field  also  used  circulating  tubes  inside  of  the  drop- 
tube. 

Fletcher,  1869. — A  vertical  fire-box  boiler,  with  horizontal  cone- 


354 


STEAM-BOILER  ECONOMY. 


shaped  tubes  radiating  from  the  sides  of  the  fire-box  towards  the 
centre. 


FIG.  105. — FLETCHER,  1869. 


FIG.  106.— MILLER,  1870. 


J.  A.  Miller,  1870. — Cast  headers,  to  which  were  fixed  closed-end 
tubes,  inclined  about  15°  from  the  horizontal,  with  inner  circulating 
tubes. 

Allen,  1871. — Cast-iron  drop-tubes  slightly  inclined  from  the  ver- 
tical, screwed  into  a  horizontal  tube  at  the  top. 


FIG.  107.— ALLEN,  1871.  FIG.  108.— WIEGAND,  1872. 

Wiegand,  1872. — Groups  of  vertical  tubes,  with  inside  circulating 
tubes,  connected  to  an  overhead  steam-  and  water-reservoir.  The 
lower  ends  of  the  tubes  were  closed  by  caps. 


TYPES  OF  STEAM-BOILERS. 


355 


W.  A.  Kelly,  1876.— Similar  to  J.  A.  Miller's  design  of  1870,  with 
some  additions,  among  them  being  superheating  tubes  for  drying  the 
steam. 


FIG.  109.— W.  A.  KELLY,  1876. 

Hazelton,  1883. — A  vertical  cylinder  with  radial  tubes,  commonly 
called  the  "Porcupine"  boiler.  The  upper  portion  of  this  boiler  is 
superheating  surface. 


FIG.  110.— HAZELTON,  1883. 


FIG.  111.— GURNET,  1826, 


BOILERS   WITH   BENT   TUBES. 

Gurney,  1826. — A  pair  of  vertical  steam-  and  water-reservoirs  were 
connected  at  their  bottom  and  about  half  way  up  their  height  by 
cross-pipes,  from  which  a  series  of  bent  tubes  were  projected  into  the 
fire-box.  The  lower  row  of  tubes  served  as  a  grate.  This  boiler  was 
used  in  a  steam  road-carriage. 


356 


STEAM-BOILER  ECONOMY. 


Church,  1832. — A  locomotive  fire-box  with  a  vertical  extension  at 
one  end,  filled  with  bent  tubes  connecting  the  sides  of  the  fire-box 
with  the  crown-sheet,  and  with  side  openings  in  the  shape  of  fire- 
tubes  extending  through  the  shell  at  the  top,  for  taking  oft2  the  gases. 
This  boiler  was  also  used  for  a  road-carriage. 


FIG.  112.— CHURCH,  1832. 


FIG.  113.— WILCOX,  1856. 


Wilcox,  1856. — Stephen  Wilcox  was  the  first  to  use  inclined  tubes 
connecting  water-spaces,  front  and  rear,  with  an  overhead  steam-  and 
water-reservoir.  The  tubes  were  bent  with  a  slightly  reversed  curve 
extending  nearly  the  whole  length  of  the  tube.  In  1869  Mr.  Wilcox, 
with  his  partner,  George  H.  Babcock,  brought  out  the  Babcock  &  Wil- 
cox boiler,  with  straight  inclined  tubes. 


FIG.  114.— ROWAN,  1865. 


FIG.  115.— PHLEGER,  1871. 


TYPES 


STEAM-BOILERS. 


357 


Rowan,  1865. — A  series  of  units  placed  side  by  side,  each  unit  con- 
sisting of  an  upper  and  a  lower  horizontal  drum  connected  by  a  series 
of  bent-ended  heating-tubes,  and  at  their  ends,  outside  the  setting, 
with  down-take  tubes  of  large  diameter. 

Phleger,  1871. — Gurney  U  tubes  were  used  for  fire-bars,  with  a 
second  series  added  above  for  heating-tubes  and  above  them  a  large 
steam-  and  water-drum. 


FIG.  116.— ROGERS  &  BLACK,  1876. 


FIG.  117.— DANCE,  1833. 


Rogers  &  Black,  1876. — A  series  of  U  tubes  on  the  outside  of  a 
vertical  shell,  surrounded  with  a  brick  setting. 

BOILERS  BUILT  OF  PIPES  AND  FITTINGS. 

Dance,  1833. — The  lower  tubes  were  used  as  grates.  Up-flow  and 
down-flow  pipes,  connected  by  special  fittings.  Steam  and  water 
capacity  very  small,  and  no  provision  for  internal  cleaning. 

Belleville,  1865. — Bent  U  tubes  screwed  into  return  bends,  a  series 
of  coils  being  placed  vertically  side  by  side,  connected  at  the  top  to  a 
separating-drum  and  at  the  bottom  to  a  common  feed-pipe. 

Belleville,  1877. — The  bent  pipe  was  discarded  and  return  bends 
used  at  both  ends  of  a  series  of  straight  tubes. 

Kilgore,  187 4. — Straight  tubes  with  return  bends,  connected  to 
cast-iron  water-chambers.  This  boiler. was  introduced  quite  exten- 
sively in  Pittsburgh,  but  it  had  a  very  short  life. 

Ward,  1879. — A  vertical  cylinder,  surrounded  by  a  series  of  con- 
centric coils  interrupted  twice  in  their  circumference,  on  opposite 


358 


STEAM-BOILER  ECONOMY. 


sides,  by  vertical  manifolds.  The  manifolds  on  one  side  were  con- 
nected by  a  radial  pipe  to  the  bottom  on  the  cylinder,  and  at  the 
other  side  to  a  circular  pipe  connecting  near  the  top  of  the  cylinder. 


FIG.  118. — BELLEVILLE,  1865.  FIG.  119. — BELLEVILLE, 

1877. 

Roberts,  1887. — Straight  pipes  with  return  bends,  with  "down- 
take"  pipes  outside. 


FIG.  120.— WARD,  1879.  FIG.  121.— KILGORE,  1874. 

Almy,  1890. — Straight  pipes  connected  with  elbows  and  return 
bends  to  an  overhead  steam-  and  water-reservoir  and  bottom  con- 
necting pipes. 

Herreshoff,  1890. — Straight  tubes  with  return  bends  at  each  end. 


TYPES  OF  STEAM-BOILERS. 


359 


FIG.  122.— ROBERTS,  1887. 


FIG.  123.— ALMY,  1890. 


BOILERS     WITH     STRAIGHT     TUBES     CONNECTED     TO     WATER-CHAMBERS 

AT    BOTH    ENDS. 

Firmenich,  1875. — Flat-sided  horizontal   drums   at  top   and   bot- 
tom of  a  bank  of  straight  tubes.     Two  such  units  were  placed  A- 


FIG.  124. — FIRMENICH,  1875. 


FIG.  125.— WHEELER,  1892. 


360  STEAM-BOILER  ECONOMY. 

fashion,  with  the  grates  between  them  at  the  bottom,  and  surmounted 
with  a  steam-drum  on  top. 

Wheeler,  1892. — Like  the  Firinenich,  but  with  the  tubes  set 
vertically,,  and  the  lower  water-drums  directly  over  the  grates. 

Maynard,  1870. — A  horizontal  steam-  and  water-cylinder  above  a 
bank  of  tubes  placed  at  a  slight  inclination  from  the  horizontal;  the 
ends  of  the  tubes  expanded  into  round  boxes  having  stayed  heads 
connected  to  the  horizontal  drum. 


FIG.  126.— MAYNARD,  1870. 

Illustrations  of  some  other  old  forms  of  boilers  will  be  found  in  the 
chapter  on  Results  of  Steam-boiler  Trials. 

Modern  Forms  of  Water-tube  Boilers. — The  water-tube  type  of 
boiler  did  not  come  into  any  extensive  use  prior  to  1870,  probably 
because  inventors  of  the  earlier  forms  did  not  appreciate  the  require- 
ments of  a  thoroughly  good  boiler,  such  as  facility  for  cleaning  and 
repair,  provisions  for  proper  circulation  of  the  water  and  of  the  gases 
of  combustion,  and  for  insuring  dry  steam — all  of  which  are  met 
in  at  least  some  of  the  modern  forms  of  the  water-tube  boiler.  In 
1867  Mr.  John  B.  Eoot  invented  what  is  known  as  the  Eoot  boiler, 
and  in  1869  the  Babcock  &  Wilcox  Company  first  put  their  boiler 
on  the  market.  Both  of  these  boilers  have  been  improved  in  some 
respects  since  they  were  first  brought  out,  the  Babcock  &  Wilcox  reach- 
ing practically  its  present  form  as  early  as  1873,  and  the  Root  boiler 
its  present  form  about  ten  years  ,later. 

The  Babcock  &  Wilcox  Boiler,  since  the  original  patents  have 
expired,  has  been  extensively  copied,  with 'modifications  more  or  less 
important,  and  its  general  form  may  now  be  considered  a  standard 
type  of  boiler,  the. leading  features  of  which  are  a  horizontal  drum. 


TYPES  OF  STEAM-BOILERS.  361 

usually  about  36  in.  diameter,,  the  water-line  being  carried  at  the 
middle  of  the  drum,  and  a  "bank"  of  4-in.  tubes  inclined  about  15° 
from  the  horizontal,  the  tubes  being  usually  laid  parallel  in  horizontal 
rows  across  the  boiler,  the  vertical  rows  being  staggered.  The  tubes 
are  expanded  at  each  end  into  headers,  which  take  different  forms 
in  different  modifications  of  the  general  type.  The  front  headers  are 


FIG.  127. — THE  BABCOCK  &  WILCOX  BOILER,  ANTHRACITE  SETTING. 

connected  with  the  drum  by  short  pieces  of  tube,  and  the  rear  headers 
by  tubes  4  to  6  ft.  long. 

In  the  most  recent  form  of  Babcock  &  Wilcox  boiler,  designed 
especially  for  high  pressures,  Fig.  127,  the  header  is  a  long  corrugated 
box  of  forged  steel,  into  whioh  are  expanded  the  tubes  of  one  of  the 
vertical  staggered  rows.  Opposite  the  end  of  each  tube  there  is  a 
hand-hole  plate,  held  to  its  seat  by  a  bolt  and  nut.  As  the  rear  header, 
as  well  as  the  front  header,  is  provided  with  similar  hand-hole  plates, 
the  interior  of  the  tube  may  be  inspected  by  the  boiler-owner  himself, 
by  having  some  one  hold  a  candle  at  the  hand-hole  of  the  rear  header 
while  he  looks  in  through  the  front  header.  The  hand-holes  are  made 
of  such  a  size  that  the  tubes  may  be  withdrawn  or  inserted  through 
them  whenever  a  tube  requires  to  be  replaced. 


362 


STEAM-BOILER  ECONOMY. 


The  furnace  shown  in  Fig.  127  is  suitable  only  for  anthracite  or 
coke.  With  soft  coal  it  would  make  dense  smoke  and  cause  the  tubes 
to  be  coated  with  soot. 

In  the  National  and  Gill  boilers,  the  principal  feature  of  difference 
from  the  Babcock  &  Wilcox  boiler  is  the  form  of  the  headers.  In  the 

National  boiler  the  header  is  of  approxi- 
mately a  triangular  shape  to  take  three  tubes, 
while  in  the  Gill  boilers  the  headers  are  made. 
as  shown  in  Fig.  128,  to  take  four,  five,  or 
six  tubes.  Each  header-box  is  connected 
with  the  one  above  it  by  an  expanded  nipple. 
The  Root  Boiler  (Fig.  129),  consists  of  an 
arrangement  of  4-in.  tubes,  inclined  about 
20°  from  the  horizontal  and  set  in  a  stag- 
gered position  vertically,  surrounded  by  sev- 
eral horizontal  steam-  and  water-drums 
about  15  ins.  in  diameter.  The  tubes  are 
expanded  into  headers  which  with  their  con- 
nections form  a  vertical  channel  through 
which  the  water  passes  from  the  point  where 
the  lower  tube  enters  them  to  the  top.  When 
the  boiler  is  working,  water  fills  the  tubes,  and 
also  about  half  of  each  of  the  overhead 
drums,  each  one  of  which  receives  the  water 
and  steam  from  the  vertical  piles  of  tubes 
immediately  below  it. 

In  the  rear  of  the  boiler,  at  the  .end  of 
the  overhead  water-drums,  each  drum  has 
a  vertical  pipe  terminating  in  a  drum 
common  to  all  beneath  it,  which  is  placed 
at  right  angles  to  them;  and  through  these 

vertical  "down-take  pipes"  flows  the  water  of  circulation,  which  has 
parted  with  its  bubbles  of  steam.  In  this  cross-drum  the  down-flowing 
water  meets  the  feed-water,  which  is  introduced  at  this  point,  and 
warms  it  up  to  a  temperature  sufficiently  high  to  prevent  any  trouble 
which  might  be  caused  by  unequal  expansion  in  the  boiler  parts  from 
receiving  feed-water  at  a  low  temperature.  From  this  feed-drum, 
the  mixture  of  feed  and  circulating  water  descends  through  the  large 
vertical  down-take  pipes  to  the  mud-drum  beneath.  After  leaving  the 
mud  drum,  the  water  passes  from  the  "goose-neck"  connections  into 


FIG.  128. — HEADERS  OP 
THE  GILL  BOILER. 


TYPES  OF  STEAM-BOILERS. 


363 


the  extreme  lower  end  of  each  one  of  the  rear  vertical  sections  of  boiler- 
tubes;  and  then  it  rises  up  along  the  tubes,  maintaining  the  constant 
upward  flow  which  is  always  going  on  when  the  boiler  is  in  operation. 


FIG.  129.— THE  ROOT  WATER-TUBE  BOILER. 

The  details  of  the  Eoot  boiler  are  shown  in  Fig.  130. 

No.  1  shows  a  "package"  consisting  of  two  tubes  with  a  header 
expanded  on  each  end.  No.  2  shows  these  packages  placed  one  upon 
the  other,  forming  a  section.  Connecting-bends  are  also  shown  in 
place,  through  which  a  circulation  of  water  is  obtained  from  the 
bottom  to  the  top  of  the  section.  A  number  of  sections  placed  side 
by  side  go  to  form  a  complete  boiler.  No.  3  shows  the  method  by 
which  these  bends  are  applied.  Between  the  bend  which  is  ready  to 
drop  in  place  and  the  header  is  seen  the  metallic  packing-ring 
which  drops  into  the  seat  beneath  it.  This  ring  is  shown  in  detail 
in  No.  4.  A  sectional  view,  No.  6,  shows  it  in  place.  All  these 
seats  are  milled  to  exact  size  by  special  machinery,  and  the  ring, 
which  is  made  of  an  elastic  bronze-like  metal,  is  also  finished  to  an 
exact  size. 

The  tapered  end  of  the  connecting-bend  is  shown  in  the  enlarged 
view,  No.  5.  When  this  plug  is  forced  down  into  the  tapered  seat  of 
the  ring  it  causes  the  ring  to  expand  in  every  direction  radially,  and 
so  make  a  tight  joint.  This  bend  is  drawn  down  into  the  seat  by 


364 


STEAM-BOILER  ECONOMY. 


bolts.  The  heads  of  these  bolts  are  ball-shaped  and  are  received 
into  similarly  shaped  sockets  cast  in  the  headers,  which  allow  the 

screw-Tends    freedom   to   move 
in  every  direction. 

All  the  water-tube  boilers 
above  mentioned,  as  well  as 
many  other  variations  of  this 
general  type,  are  known  as 
sectional  boilers,  since  they  are 
built  up  of  sections  made  by 
assembling  a  number  of  inter- 
changeable parts.  This  sec- 
tional feature  is  a  convenience 
in  transportation  and  erection, 
and  it  facilitates  the  rapid 
making  of  repairs,  a  new  sec- 
tion being  easily  substituted 
for  an  old  one. 

Other  water-tube  boilers 
are  made  which  are  not  sec- 
tional. One  of  the  best  known 
is  the  Heine  boiler,  shown  in 
Fig.  21,  p.  219.  The  tubes  are 
parallel  with  the  drum,  both 
being  inclined  at  the  same  an- 
gle when  the  boiler  is  set  up, 
and  are  connected  with  it  at 

each  end  by  large  water-legs,  made  of  plates  stayed  together.  A 
hand-hole  plate  is  opposite  the  end  of  each  tube,  through  which  the 
tube  may  be  cleaned  or  replaced. 

It  will  be  noticed  that  in  the  Heine  boiler,  Fig.  21,  the  passages 
for  the  gases  of  combustion  are  horizontal,  or  parallel  with  the 
tubes,  while  in  the  other  boilers  the  gases  pass  transversely  across 
the  tubes  three  times.  For  anthracite  coal  the  transverse  passages  are 
probably  the  best,  and  when  properly  fired  this  coal  is  thoroughly 
burned  on  the  grates,  and  the  direction  of  the  gas-passages  across 
the  tubes  offers  every  facility  that  can  be  desired  for  allowing  the 
heating  surface  to  absorb  the  heat  from  the  gases.  With  bituminous 
coal,  the  settings  shown  in  Figs.  127  and  129  do  not  offer  sufficient 
opportunity  for  the  gases  from  the  coal  to  be  thoroughly  burned 


FIG.  130. — DETAILS  OF  THE  ROOT  BOILER. 


TYPES  OF  STEAM-BOILERS. 


365 


before  they  reach  the  tubes,  consequently  a  portion  of  the  valuable 
heating  gases  is  apt  to  go  off  unburned,  since  the  tubes  chill  them 
below  the  temperature  of  ignition.  The  long  horizontal  passage 
under  the  lower  row  of  tubes  is  better  for  insuring  combustion  of 
the  gases,  but  the  return  passage  enclosing  the  tubes  requires  to  be 
carefully  proportioned  as  to  its  sectional  area,  in  relation  to  the 
amount  of  coal  burned,  so  that  the  hot  gases  do  not  travel  along 
the  upper  portion  of  the  passage,  only,  leaving  the  heating  surface  of 
the  lower  portion  ineffective.  In  adopting  either  one  of  these 
styles  of  setting,  with  bituminous  coal,  there  is  a  choice  of  evils:  in 
one  style  the  gas  may  be  imperfectly  burned,  in  the  other  the  heat 
from  the  burned  gas  may  be  imperfectly  absorbed.  With  furnaces 
adapted  to  the  complete  combustion  of  the  gases  of  bituminous  coal, 
the  transverse  passage  will  usually  be  found  preferable  to  the  longitu- 
dinal. 


LONGITUDINAL  VERTICAL  SECTION 


HALF  SECTION 
AT  A-A 


HALF  SECTION 
AT  B-8 


FIG.  131. — HEINE  BOILER  WITH  SUPERHEATER. 


The  Setting  of  a  Heine  Boiler  with  Superheater  is  shown  in  Fig. 
131.  The  superheater  consists  of  two  parts,  one  on  each  side  of  the 
drum.  Each  superheater  is  located  above  the  water  line,  in  a  fire- 
brick chamber  formed  in  the  setting,  as  shown.  A  flue  connects  the 
chamber  directly  with  the  furnace,  and  a  small  per  cent  of  the 
furnace  gases  flow  up  the  flue  and  supply  the  heat  to  the  superheater 
tubes.  The  hot  gases  pass  over  the  superheater  tubes,  and  then  flow 
out  of  the  superheater  chamber  at  the  end  nearest  the  front  header, 
so  that  before  reaching  the  uptake  and  joining  the  boiler  gases,  they 


366 


STEAM-BOILER  ECONOMY. 


pass  under  the  boiler  drum.  A  damper  in  the  superheater  outlet 
controls  the  amount  of  gases  flowing  over  the  tubes,  thus  permitting 
temperature  regulation  and  also  cutting  off  the  supply  of  hot  gases 
when  saturated  steam  is  desired,  or  when  here  is  no  boiler  load.  No 
provision  is  made  for  flooding  the  superheater  as  that  operation  is 
unnecessary. 

The  superheaters  are  made  of  IJ-in.  seamless-drawn  tubing,  bent 
into  U-form,  and  expanded  into  box  headers  of  a  rectangular  shape. 
Hollow  stay-bolts  in  the  headers  permit  of  cleaning  of  soot  from  the 
superheater  tubes,  and  hand-hole  plates  are  provided  for  access  to 
the  tube  ends.  Within  the  headers  there  are  two  partition  plates 
dividing  the  superheater  box  into  three  chambers  and  causing  the 
steam  to  flow  through  the  tubes  in  four  passes. 


FIG.  132. — THE  STIRLING  BOILER. 

The  Stirling  Boiler,  Fig.  132,  consists  of  three  horizontal  steam- 
and  water-drums  at  the  top,  and  a  single  water-drum  at  the  bottom, 
connected  by  three  sets  of  inclined  and  somewhat  curved  tubes.  A 
fire-brick  arch  is  built  above  the  grate,  and  baffle-walls  of  fire-brick 
are  placed  above  the  upper  rows  of  two  of  the  sets  of  tubes,  which 
give  a  proper  direction  to  the  heated  gases. 

The  Wickes  Boiler,  Fig.  133,  also  consists  of  an  upper  and  lower 
drum  connected  by  vertical  tubes.  By  building  a  thin  wall  of  fire- 


TYPES  OF  STEAM-BOILERS. 


367 


brick  between  two  adjoining  middle  rows  of  tubes,  as  shown  in  the 
cut,  the  passage  for  gas  is  caused  to  lead  first  upwards  from  the  fur- 


FIG.  133.— THE  WICKES^BOILER. 

nace  and  then  downwards  to  the  chimney-flue.    An  external  furnace 
is  used  with  this  boiler. 

The  Rust  Water-tube  Boiler. — This  boiler,  one  style  of  which 
is  shown  in  Fig.  134.  consists  of  two  transverse  steam-and- water  drums 
and  two  transverse  water-and-mud  drums,  set  parallel  and  connected 
by  banks  of  tubes.  Each  steam-and-water  drum  is  placed  directly 
over  a  water-and-mud  drum,  with  which  it  is  connected  by  five  rows 
of  straight  vertical  tubes  and  one  row  of  curved  tubes.  The  rows 


368 


STEAM-BOILER  ECONOMY. 


of  tubes  are  parallel  with  the  bridge  wall  for  the  full  width  of  the 
furnace.  The  steam-and-water  drums  are  connected  by  one  row  of 
short  circulating  tubes  below  the  water  line,  and  by  a  row  of  steam 
tubes  connecting  the  steam  spaces  above  the  water  line,  these  steam 


FIG.  134. — THE  RUST  WATER-TUBE   BOILEE. 

tubes  being  grouped  near  the  ends  of  the  drums.  The  main  steam 
outlet  is  placed  at  the  top  and  center  of  the  rear  steam-and-water 
drum.  The  water-and-mud  drums  are  connected  by  a  row  of  short 
horizontal  circulating  tubes. 

Each  drum  is  made  up  of  two  sheets  with  longitudinal  riveted 
seams.  One  of  these  sheets  is  pressed  to  form  tube  seats  which  permit 


TYPES  OF  STEAM-BOILERS. 


369 


the  use  of  straight  tubes  expanded  direct  into  the  cylindrical  drum — 
(system  is  patented).  The  drum  heads  and  manhole  plates  are  of  forged 
steel.  The  tubes  are  staggered  and  spaced  so  as  to  leave  room  between 
the  tubes  of  the  outside  rows  to  remove  those  of  the  inner  rows,  and 
replace  any  tube  without  disturbing  any  other  tube  or  any  of  the 
brickwork.  After  a  defective  tube  has  been  removed  it  is  passed  out 
through  a  door  in  the  side  of  the  setting. 

In  another  style  of  the  Eust  boiler  the  two  rows  of  vertical  curved 
tubes  are  eliminated  and  a  heavy  fire-brick  baffle  wall  supported  from 
the  ground  is  substituted  for  the  lighter  baffle  wall.     This  boiler  is 
designed  for  locations  where  straight  tubes  only  are  desired.     The- 
Eust  boiler  is  manufactured  by  the  Babcock  &  Wilcox  Co. 


FIG.  135. — THE  PARKER  BOILER. 

The  Parker  Boiler  is  shown  in  Fig.  135.  It  consists  of  one 
or  more  horizontal  steam  and  water  drums  mounted  above  two  or 
more  banks  of  horizontal  tubes.  Fire-brick  tile  are  supported  by 
the  bottom  row  of  tubes  in  the  lowest  bank,  to  form  a  roof .  over 


370 


STEAM-BOILER  ECONOMY. 


the  combustion  chamber,  and  above  the  top  row  of  tubes  in  each 
of  the  banks  so  as  to  baffle  the  gases  and  cause  them  to  travel  along 
the  tubes.  Feed  water  is  introduced  at  one  end  of  the  upper  bank 
of  tubes  and  all  the  banks  are  supplied  with  water  from  the  over- 
head drum  through  downflow  pipes  leading  from  the  bottom  of  the 
drum  (see  pipe  connection  at  the  right  hand  of  the  cut).  The 
water  circulates  downward  through  the  elements  or  sections  of  the 
upper  bank  (known  as  the  economizer),  being  heated  as  it  travels 
by  the  gases  which  have  been  reduced  in  temperature  by  their 
passage  through  the  lower  banks,  and  is  finally  discharged  through 
upcast  pipes  into  the  rear  head  of  the  drum  above  the  diaphragm. 
The  water  then  flows  along  the  diaphragm  into  the  scale  pocket 
at  the  other  end  of  the  drum,  then  through  a  swinging  non-return 
gate  covering  a  manhole  leading  into  the  lower 
chamber  of  the  drum,  thence  into  the  downcast 
circulating  pipes  into  the  lower  banks  of  tubes. 
Each  element,  or  nest  of  tubes,  in  the  banks  is 

ii  r  T r  ATX  provided  with  a  non-return  valve  in  the  inlet 
'bfo  O  6  OlOiQl  kox,  which  prevents  the  reversal  of  the  flow 
of  water.  The  boiler  shown  in  the  cut  is  equip- 
ped for  oil  burning,  and  has  a  small  super- 
heating coil  in  the  combustion  chamber  and  a 
large  superheating  drum  under  the  roof  of  the 
setting  and  between  the  two  steam  and  water 
drums.  It  is  rated  at  645  H.P.  or  6450  sq.  ft. 
of  heating  surface.  It  contains  280  4-in.  tubes, 
of  which  246  are  20  ft.  long,  17  are  20.5  ft.  and 
17  are  22.5  ft.  long,  two  steam  and  water  drums 
4^  by  22  ft.,  one  superheater  steam  drum  18 
in.  by  20  ft.,  and  32  loops  of  1%  in.  tubes,  or  107.5  sq.  ft.  in  the 
superheating  coils.  Fig.  136  is  a  diagram  of  the  circulation  system 
of  the  Parker  boiler. 

Water-tube  Marine  Boilers. — Of  the  boilers  built  of  pipes  and 
fittings,  briefly  described  on  page  357,  the  Ward,  Roberts,  Almy  and 
Herreshoff  have  been  somewhat  extensively  used  in  steam-yachts  and 
torpedo-boats.  The  Belleville,  in  its  recent  forms,  has  come  largely 
into  use  in  the  French  mercantile  marine,  and  has  been  adopted  in 
several  ships  of  war,  including  large  cruisers,  in  the  British  Navy. 
For  descriptions  and  illustrations  of  many  other  forms  of  marine 
water-tube  boilers  see  Bertin  &  Robertson  on  "Marine  Boilers"  and 


FIG.  136.— CIRCULA- 
TION OF  THE  PAR- 
KER BOILER. 


TYPES  OF  STEAM-BOILERS.  371 

W.  S.  Hutton  on  "Steam-Boiler  Construction."    Some  of  these  forms 
are  described  below. 

The  Thornycroft  Boiler  (Fig.  137).  A  large  cylindrical  steam- 
drum  is  connected  to  a  lower  water-drum  by  two  groups  of  curved 
eter.  The  fire-grates  are  on 
generating  tubes  of  small  diam- 
each  side  of  the  water-drum.  The 
two  outer  rows  of  tubes  of  each 
group  are  brought  together,  mak- 
ing a  tube-wall,,  but  so  as  to  leave 
openings  for  the  hot  gases  to 
pass  between  the  tubes  near  their 
lower  ends.  The  two  inner  rows 
of  each  group  are  in  like  manner 
brought  together,  except  near 
their  upper  ends,  where  there 
are  passages  left  between  them.  FlG-  ^.-THORNYCROFT  BOILER. 
The  gases  thus  pass  from  the  combustion-chamber  above  the  grates  on 
each  side  into  the  flue  between  the  outer  and  inner  tube-walls,  and 
thence  into  the  heart-shaped  central  flue  which  leads  to  the  funnel  at 
the  back  of  the  boiler.  The  outer  sides  of  the  fire-box  or  combustion- 
chamber  are  formed  by  tube-walls  leading  from  two  small  water-drums 
into  the  upper  part  of  the  steam-drum,  these  water-drums  being 
connected  by  a  cross-pipe  at  the  back  of  the  boiler.  The  generating 
tubes  discharge  a  mingled  mass  of  steam  and  water  into  the  steam- 
drum,  in  which  there  are  baffle-plates  to  separate  the  steam  and  the 
water.  The  steam  passes  into  an  internal  steam-pipe  through  narrow 
slits,  while  the  water  falls  to  the  bottom  of  the  steam-drum  and  is 
thence  conveyed  by  large  central  return-pipes  to  the  water-drum  at 
the  bottom,  thus  insuring  a  rapid  circulation.  The  following  data  of  a 
large  Thornycroft  boiler  are  given  by  Hutton : 

Tube  surface sq.ft.  4020 

Fire-grate  area "     63 . 5 

Weight  of  the  boiler  and  mountings,  with  water tons    18j 

Indicated  horse-power  on  trial,  with  triple-expansion  engines 2000 

Working  pressure  of  steam Ibs.'per  sq.in.    220 

This  boiler  is  known  as  the  "Daring"  type.  Other  and  smaller 
boilers  of  the  Thornycroft  make  are  called  the  "Speedy"  and  the 
"Launch"  types.  The  Thornycroft  boiler  is  largely  used  in  torpedo- 
boats  and  high-Speed  yachts,  especially  in  Great  Britain. 


372 


STEAM-BOILER  ECONOMY. 


FIG.  138. — THE  MOSHER  BOILER. 


The  Mosher  Boiler  (Fig.  138).  Two  steam-  and  water-drums  com- 
municate with  lower  water-chambers  by  a  great  number  of  curved 

tubes  of  small  diameter,  and  also  by 
two  external  down-take  tubes,  4 
inches  in  diameter.  The  front  and 
back  casings  are  lined  with  fire- 
brick covered  with  asbestos,  and  the 
upper  part  with  a  layer  of  soap- 
stone  between  layers  of  asbestos. 
This  boiler  is  used  in  many  high- 
speed American  yachts. 

Fig.  139  shows  a  later  form  of 
the  Mosher  boiler,  known  as  type  B. 

Boilers  of  this  type  were  used  in  the  U.  S.  battleships  Kearsarge  and 
Kentucky.  Another 
form,  type  A,  is  similar 
to  type  B,  but  has  two 
banks  of  tubes,  more 
steeply  inclined  than 
those  shown  in  Fig. 
139,  connected  with  a 
single  overhead  drum, 
and  placed  over  a 
wide  A-shaped  fur- 
nace. 

The  Yarrow  Boiler, 
shown  in  Fig.  276, 
page  654,  is  similar  in 
form  to  the  type  A 
Mosher  boiler.  It  is 
largely  used  for  ma- 
rine purposes  in  Eu- 
rope. 

The  Babcock  &  Wilcox  Marine  Boiler  is  shown  in  Fig.  140,  which 
represents  one  of  the  boilers  of  the  U.  S.  cruiser  Cincinnati.  This 
boiler  has  been  extensively  adopted  in  the  British  and  American  navies 
for  the  largest  war- vessels,  and  since  1885  it  has  been  used  with  great 
success  in  the  Wilson  (British)  line  of  merchant  steamers.  The 
chief  features  in  which  it  differs  from  the  land  type  of  the  Babcock  & 


FIG.  139. — MOSHER  BOILER,  TYPE  B. 


TYPES  OF  STEAM-BOILERS.  373 

Wilcox  boiler,  Fig.  127,  page  361,  have  been  designed  for  the  purpose, 
chiefly,  of  providing  a  very  large  area  of  grate  and  heating  surface, 
together  with  relatively  small  weight  of  metal  and  water  to  be  carried 
in  the  contracted  space  allowed  in  ocean  steamers.  The  tubes  in  the 


FIG.  140. — LONGITUDINAL  SECTION  OF  BABCOCK  &  WILCOX  MARINE  WATER- 
TUBE  BOILER,  '"  ALERT  "  TYPE,  SHOWING  SIDE  CASING  REMOVED. 

lower  row  are  4  ins.  diameter,  all  others  being  2  ins.  The  steam 
and  water  drum  is  set  transversely  to  the  direction  of  the  tubes.  The 
fire-box  is  roofed  over  by  fire-brick  supported  by  the  lower  row  of 
tubes.  The  fire-door  is  placed  at  what  would  be  called  the  rear  of  the 
boiler  in  the  ordinary  land  boiler.  A  fuller  description  of  this  boiler, 
together  with  the  record  of  a  series  of  tests  made  by  engineers  of  the 


374 


STEAM-BOILER  ECONOMY. 


U.  S.  Navy  will  be  found  in  the  chapter  on  Results  of  Steam-Boiler 
Trials. 

Forms  of  Boiler  used  in  Different  Countries.— The  average  boiler- 
user  is  governed  in  his  selection  of  a  boiler  largely  by  local  custom  and 
prejudice,  and  therefore  different  forms  of  boiler  are  the  favorites  in 
different  parts  of  the  world.  To  show  how  generally  this  is  true,  we 
have  the  following  figures  showing  the  percentage  of  various  types  of 
boilers  used  in  Great  Britain,  France,  Germany,  Switzerland,  and 
Austria,  prepared  by  Mr.  Killer,  of  the  National  Boiler  Insurance  Co., 
of  Manchester,  England,  and  given  by  Mr.  R.  S.  Hale  in  Circular  No. 
5,  1896,  of  the  Steam  Users'  Association,  Boston  Mass. : 

PEB  CENT  OF  BOILERS   OF  VARIOUS  TYPES  USED   IN  EUROPE. 


1895 

1893-4 

United 
Kingdom. 

France. 

Germany. 

Switzer- 
land. 

Austria. 

Lancashire  and  similar  types  . 
Cornish  and  similar  types.  .  .  . 
Externally  fired  cylindrical.  .  . 
Externally  fired  multi-tubular 
Locomotive  

38.0 
23.7 

f6.8 

4.7 
8.2 
57.3 
13.4 
5.1 
3.6 
5.7 
2.0 

35.7 
15.3 
14.8 
5.2 
17.3 
5.0 
4.6 
2.1 

19.6 
40.8 
15.5 
3.5 
5.7 
13.5 
1.4 

* 

* 

41.0 
7.5 
10.5 
6.1 
3.8 
1.4 

11.0 
16.6 
1.8 
2.1  - 

Small  verticals 

Water-tube  

Other  types 

Lancashire,  Cornish  and  similar  types,  29.7. 


t  Including  "  elephant  "  boilers 


We  note  from  this  table  that  the  Lancashire,  Cornish,  and  similar 
types  form  a  majority  of  all  the  boilers  in  the  United  Kingdom,  Ger- 
many, and  Switzerland ;  that  the  externally  fired  cylindrical,  including 
the  elephant  boilers,  are  in  the  lead  in  France  and  Austria,  and  that 
the  externally  fired  multi-tubular  boiler,  which  is  the  most  common 
boiler  in  the  United  States,  does  not  appear  to  be  used  at  all  in  Great 
Britain,  and  but  to  a  small  extent  in  other  European  countries.  If 
the  table  had  included  boilers  in  the  United  States,  it  would  probably 
put  the  externally  fired  multi-tubular  boilers  far  in  the  lead  of  all  the 
others,  the  elephant,  the  Cornish,  and  the  Lancashire  boilers  would 
not  appear  at  all,  the  externally  fired  cylindrical  boilers  to  probably 
less  than  5  per  cent,  the  small  verticals  would  have  had  a  larger 
percentage  than  in  any  country  in  Europe,  large  verticals,  such  as  the 
Manning,  which  are  not  named  in  the  European  list,  would  have 
shown  a  small  percentage,  and  water-tube  boilers  probably  a  higher 
percentage  than  anywhere  in  Europe. 


TYPES  OF  STEAM-BOILERS.  375 

It  must  be  said  in  relation  to  this  table,  that  it  is  not  fairly  repre- 
sentative of  European  practice  in  the  purchase  of  new  boilers  at  the 
present  date,  but  is  simply  the  percentage  of  boilers  in  use  in  1895,  in- 
cluding both  old  and  new;  many  of  them. were  no  doubt  forty  years 
old,  or  more.  If  a  table  were  prepared  of  the  percentages  of  boilers  of 
various  types  now  sold,  it  would  undoubtedly  show  a  much  higher 
percentage  of  water-tube  boilers,  which  have  within  the  last  ten  years 
become  very  common  in  Belgium,  France,  and  Germany,  and  are 
rapidly  increasing  in  favor  in  England  as  well  as  in  the  United  States. 

There  is  nothing  in  the  steam-engine  practice  of  different  countries, 
nor  in  the  character  of  fuel,  or  of  water  used,  which  will  account  for 
the  great  difference  in  boiler  practice  in  the  different  countries, 
and  the  only  explanation  of  it  appears  to  be  local  custom,  prejudice, 
and  conservatism.  The  difference  between  American  and  European 
practice  may  be  partly  explained  by  financial  considerations.  In 
England,  where  manufacturing  establishments  are  generally  of  many 
years'  standing  and  provided  with  abundant  capital,  and  where  the 
interest  on  money  is  low,  the  first  cost  of  a  boiler-plant  is  usually  a 
consideration  of  secondary  importance.  This  has  led  to  the  general 
introduction  of  the  Lancashire  boiler,  which  is  very  high  in  first  cost. 
In  America,  where  most  of  the  manufacturing  concerns  have  grown 
from  small  beginnings,  where  capital  for  investment  in  manufacturing 
has  been  scarce  and  interest  high,  low  first  cost  has  been  considered 
of  chief  importance,  and  on  this  account  the  horizontal  multi- tubular 
boiler,  which  is  almost  unknown  in  England,  has  come  into  most  ex- 
tensive use.  In  recent  years,  however,  in  the  United  States,  the  in- 
crease of  wealth,  the  decrease  of  the  rate  of  interest,  the  growth  of 
manufacturing  concerns  into  establishments  of  vast  extent  and  abund- 
ant capital,  the  decrease  of  the  margin  of  profit  in  manufactured 
goods,  and  intense  competition,  have  all  tended  to  bring  about  changes 
in  the  ideas  and  methods  of  manufacturers  and  other  steam-users. 
They  are  now  disposed  to  look  more  carefully  Into  the  questions  of  econ- 
omy of  fuel  and  of  durability  of  steam-boilers,  and  are  more  willing 
than  formerly  to  try  boilers  of  higher  first  cost  if  they  can  be  assured 
of  an  ultimate  saving  in  annual  expense. 


CHAPTER  XI. 

BOILER  HORSE-POWER—PROPORTIONS  OF  HEATING  AND  GRATE 
SURFACE— PERFORMANCE  OF  BOILERS. 

The  Horse-power  of  a  Steam-boiler. — The  term  "horse-power"  has 
two  meanings  in  engineering:  First  f  an  absolute  unit  or  measure  of 
the  rate  of  work;  that  is,  of  the  work  done  in  a  certain  definite  period 
of  time,  by  a  source  of  energy,  as  a  steam-boiler,  a  waterfall,  a  current 
of  air  or  of  water,  or  by  a  prime  mover,  as  a  steam-engine,  a  water^ 
wheel,  or  a  wind-mill.  The  value  of  this  unit,  whenever  it  can  be 
expressed  in  foot-pounds  of  energy,  as  in  the  case  of  steam-engines, 
water-wheels,  and  waterfalls,  is  33,000  foot-pounds  per  minute.  In 
the  case  of  boilers,  where  the  work  done,  the  conversion  of  water  into 
steam,  cannot  be  expressed  in  foot-pounds  of  available  energy,  the 
value  given  to  the  term  horse-power  is  the  evaporation  of  34£  Ibs. 
of  water  per  hour  from  212°  into  steam  at  the  same  temperature, 
which  is  equivalent,  very  nearly,  to  the  evaporation  of  30  Ibs.  of 
water  of  a  temperature  of  100°  F.  into  steam  at  70  Ibs.  pressure  above 
the  atmosphere.  Both  of  these  units  are  arbitrary;  the  first,  33,000 
foot-pounds  per  minute,  orginally  used  by  James  Watt,  being  con- 
sidered equivalent  to  the  power  exerted  by  a  good  London  draft- 
horse,  and  the  second,  30  Ibs.  of  water  evaporated  per  hour,  being 
considered  to  be  the  steam  requirement  per  indicated  horse-power  of 
an  average  engine,  and  100°  F.  and  70  Ibs.  the  average  conditions  of 
boiler  practice  (in  1876). 

The  second  definition  of  the  term  horse-power  is  an  approximate 
measure  of  the  size,  capacity,  value,  or  "rating"  of  a  boiler,  engine, 
water-wheel,  or  other  source  or  conveyer  of  energy,  by  which  measure 
it  may  be  described,  bought  and  sold,  advertised,  etc.  No  definite 
value  can  be  given  to  this  measure,  which  varies  largely  with  local 
custom  or  individual  opinion  of  makers  and  users  of  machinery.  The 
nearest  approach  to  uniformity  which  can  be  arrived  at  in  the  term 
"horse-power,"  used  in  this  sense,  is  to  say,  that  a  boiler,  engine, 
water-wheel  or  other  machine,  "rated"  at  a  certain  horse-power, 
?hould  be  capable  of  steadily  developing  that  horse-power  for  a  long 
period  of  time  under  ordinary  conditions  of  use  and  practice,  leaving 
to  local  custom,  to  the  judgment  of  the  buyer  and  seller,  to  written 

376 


BOILER  HORSE-POWER.  377 

contracts  of  purchase  and  sale,  or  to  legal  decisions  upon  such,  con- 
tracts, the  interpretation  of  what  is  meant  by  the  term  "ordinary 
conditions  of  use  and  practice."  (Trans.  A.  S.  M.  E.,  vol.  vii.  p.. .226.) 
Definitions  of  "Boiler  Horse-power." — The  question  of  defining 
the  "commercial"  horse-power  of  a  steam-boiler  was  considered  by 
the  two  committees  on  steam-boiler  trials  (1885  and  1899)  of  the 
American  Society  of  Mechanical  Engineers.*  The  second  committee 
(1899)  reported  on  this  subject  as  follows: 

The  Committee  recommends  that,  as  far  as  possible,  the  capacity 
of  a  boiler  be  expressed  in  terms  of  the  "number  of  pounds  of  water 
evaporated  per  hour  from  and  at  212  degrees."  It  does  not  seem 
expedient,  however,  to  abandon  the  widely-recogniz-ed  measure  of 
capacity  of  stationary  or  land  boilers  expressed  in  terms  of  "boiler 
horse-power." 

The  unit  of  commercial  boiler  horse-power  adopted  by  the  Com- 
mittee of  1885  was  the  same  as  that  used  in  the  reports  of  the  boiler- 
tests  made  at  the  Centennial  Exhibition  in  1876,  namely,  ...  an 
evaporation  of  30  pounds  of  water  per  hour  from  a  feed-water  tem- 
perature of  100  degrees  Fahr.  into  steam  at  70  pounds  gauge-pressure, 
which  shall  be  considered  to  be  equal  to  34J  units  of  evaporation; 
that  is,  to  34J  pounds  of  water  evaporated  from  a  feed-water  tem- 
perture  of  212  degrees  Fahr.  into  steam  at  the  same  temperature. 

The  Committee  of  1899  accepted  the  same  standard,  but  reversed 
the  order  of  two  clauses  in  the  statement,  and  slightly  modified  them, 
so  as  to  read  as  follows : 

The  unit  of  commercial  horse-power  developed  by  a  boiler  shall  be 
taken  as  34|  units  of  evaporation  per  hour;  that  is,  34|  pounds  of 
water  evaporated  per  hour  from  a  feed-water  temperature  of  212  de- 
grees Fahr.  into  dry  steam  of  the  same  temperature.  This  standard 
is  equivalent  to  33,317  British  thermal  units  per  hour.  It  is  also 
practically  equivalent  to  an  evaporation  of  30  pounds  of  water  from  a 
feed-water  temperature  of  100  degrees  Fahr.  into  steam  at  70  pounds 
gauge-pressure,  f 

*  Trans.  A.  S.  M.  E.,  vols.  vi.  and  xii. 

f  The  figure  33,317  is  based  on  the  old  steam  tables,  in  which  an  evaporation 
of  1  Ib.  of  water  from  and  at  212°  was  equivalent  to  965.7  B.T.U.  By  the  new 
steam  tables  (Marks  and  Davis,  1910),  in  which  the  value  of  the  thermal  unit 
is  T¥o  of  the  heat  required  to  raise  the  temperature  of  1  Ib.'of  water  from  32° 
to  212°  F.,  the  value  of  the  unit  of  evaporation  is  970.4  B.T.U.,  and  the  com- 
mercial horse-power  is  then  34.5X970.4  =  33,478.8  B.T.U.  The  evaporation  of 
30  Ibs.  of  water  at  100°  F.  into  steam  of  70  Ibs.  gauge  pressure  is  equivalent  to 
33,461  B.T.U. 


378  STEAM-BOILER  ECONOMY. 

The  Committee  also  indorsed  the  statement  of  the  Committee  of 
1885  concerning  the  commercial  rating  of  boilers,  changing  somewhat 
its  wording  so  as  to  read  as  follows : 

A  boiler  rated  at  any  stated  capacity  should  develop  that  capacity 
when  using  the  best  coal  ordinarily  sold  in  the  market  where  the  boiler 
is  located,  when  fired  by  an  ordinary  fireman,  without  forcing  the  fires, 
while  exhibiting  good  economy ;  and  further,  the  boiler  should  develop 
at  least  one-third  more  than  the  stated  capacity  when  using  the  same 
fuel  and  operated  by  the  same  fireman,  the  full  draft  being  employed 
and  the  fires  being  crowded;  the  available  draft  at  the  damper,  unless 
otherwise  understood,  being  not  less  than  !/2  inch  water-column. 

The  A.  S.  M.  E.  Committee  on  Power  Tests,  in  its  revised  report, 
(1915)  omitted  the  above  statement  in  view  of  the  facts  that  in 
modern  power  plant  practice,  with  mechanical  stokers,  forced  draft 
and  gas  analyses,  boilers  are  often  called  upon  to  develop  during  times 
of  "peak  load"  from  two  to  three  times  their  normal  rating,  and  that 
the  overload  capacity  of  a  boiler  depends  more  upon  the  furnace  con- 
ditions than  upon  the  boiler  itself.  It  reaffirmed  the  definition  of  a 
boiler  horse-power  as  an  evaporation  of  34.5  Ibs.  of  water  per  hour 
from  and  at  212°,  and  said : 

Contracts  for  power-plant  apparatus  should  specify  the  leading 
dimensions  of  the  apparatus  and  its  rated  capacity.  If  a  specific 
guarantee  of  capacity  is  made,  either  working  or  maximum  capacity, 
the  operating  conditions  under  which  the  guarantee  is  to  be  met 
should  be  clearly  set  forth ;  such,  for  example,  as  steam  pressure,  speed, 
vacuum,  quality  of  fuel,  force  of  draft,  etc.  Likewise  if  a  contract 
contains  a  guarantee  of  economy  all  the  conditions  should  be  fully 
specified. 

The  commercial  rating  of  capacity  determined  on  for  power-plant 
apparatus,  whether  for  the  purpose  of  contracts  for  sale,  or  otherwise, 
should  be  such  that  a  sufficient  reserve  capacity  beyond  the  rating 
is  available  to  meet  the  contingencies  of  practical  operation;  such 
contingencies,  for  example,  as  the  loss  of  steam  pressure  and  capacity 
due  to  cleaning  fires,  inferior  coal,  oversight  of  the  attendants,  sud- 
den demand  for  an  unusual  output  of  steam  or  power,  etc. 

Measures  for  Comparing  the  Duty  of  Boilers. — The  measure  of 
the  efficiency  of  a  boiler  is  the  number  of  pounds  of  water  evaporated 
per  pound  of  combustible  of  a  stated  quality,  the  evaporation  being 
reduced  to  the  standard  of  "from  and  at  212°";  that  is,  the  equivalent 
evaporation  from  feed-water  at  a  temperature  of  212°  F.  into  steam  at 
the  same  temperature. 


BOILER  HORSE-POWER.  370 

Efficiency  is  usually  expressed  as  a  percentage,  and  it  is  defined 
as  follows: 
Efficiency  of  the  boiler  and  furnace 

Heat  absorbed  per  pound  of  combustible  burned ^ 

Heating  value  of  1  Ib.  of  combustible 
Efficiency  of  the  boiler  furnace  and  grate 

Heat  absorbed  per  pound  of  coal  fired 
Heating  value  of  1  Ib.  of  coal 

The  heat  absorbed  is  the  product  of  the  pounds  of  water  evaporated 
per  pound  of  coal  (or  combustible)  by  970.4.  Combustible  is  defined 
as  coal  free  of  moisture  and  ash. 

The  measure  of  the  capacity  of  a  boiler  is  the  number  of  pounds  of 
water  evaporated  from  and  at  212°  F.  per  hour,  or  it  is  the  amount  of 
"boiler  horse-power"  developed,  a  horse-power  being  defined  as  the 
evaporation  of  34J  Ibs.  of  water  per  hour  from  and  at  212°. 

The  measure  of  relative  rapidity  of  steaming  of  boilers  is  the 
number  of  pounds  of  water  evaporated  from  and  at  212°  per  hour  per 
square  foot  of  water-heating  surface. 

The  measure  of  relative  rapidity  of  combustion  of  fuel  in  boiler- 
furnaces  is  the  number  of  pounds  of  coal  burned  per  hour  per  square 
foot  of  grate  surface. 

Proportions  of  Grate  and  Heating  Surface  required  for  a  given 
Commercial  Horse-power.— ( 1  H.P.  =  34.5  Ibs.  from  and  at  212°  F.) 

Average  proportons  for  maximum  economy  for  land  boilers  fired 
with  good  anthracite  coal  (ordinary  hand  firing)  : 

Heating  surface  per  horse-power 11.5  sq.  ft. 

Grate  "         " 1/3      " 

Ratio  of  heating  to  grate  surface 34.5 

Water    evaporated  from  and  at  212°  per  sq.  ft.  H.S. 

per  hour 3     Ibs. 

Combustible  burned  per  H.P.  per  hour 3       " 

Coal  with  1/6  refuse,  Ibs.  per  H.  P.  per  hour 3.6   " 

Combustible  burned  per  sq.  ft.  grate  per  hour 9 

Coal  with  1/6  refuse,  Ibs.  per  sq.  ft.  grate  per  hour. . . .   10.8  " 
Water  evaporated  from  and  at  212°  perlb.  combustible  11.5   " 

"      "      "     "       "     "coal  (1/6  ref- 
use      9.6   " 

Heating  Surface. — For  maximum  economy,*  with  any  kind  of  fuel 
a  boiler  should  be  proportioned  so  that  at  least  one  square  foot  of  heat- 

*  The  word  "  economy  "  in  this  paragraph  means  economy  of  fuel  only. 
For  total  economy  of  annual  expenditure,  the  first  cost  of  plant,  interest,  taxes, 
depreciation,  etc.,  must  also  be  considered. 


380  STEAM-BOILER  ECONOMY. 

ing  surface  should  be  given  for  every  3  Ibs.  of  water  to  be  evaporated 
from  and  at  212°  P.  per  hour.  Still  more  liberal  proportions  are 
required  if  a  portion  of  the  heating  surface  has  its  efficiency  reduced 
by:  1.  Tendency  of  the  heated  gases  to  short-circuit;  that  is  to  select 
passages  of  least  resistance  and  flow  through  them  with  high  velocity, 
to  the  neglect  of  other  passages.  2.  Deposition  of  soot  from  smoky 
fuel.  3.  Incrustation.  If  the  heating  surfaces  are  clean,  and  the 
heated  gases  pass  over  them  uniformly,  little  if  any  increase  in 
economy  can  be  obtained  by  increasing  the  heating  surface  beyond  the 
proportion  of  1  sq.  ft.  to  every  3  Ibs.  of  water  to  be  evaporated,  and 
with  all  conditions  favorable  but  little  decrease  of  economy  will  take 
place  if  the  proportion  is  1  sq.  ft.  to  every  4  Ibs.  evaporated ;  but  in 
order  to  provide  for  driving  of  the  boiler  beyond  its  rated  capacity, 
and  for  possible  decrease  of  efficiency  due  to  the  causes  above  named, 
it  is  better  to  adopt  1  sq.  ft.  to  3  Ibs.  evaporation  per  hour  as  the 
minimum  standard  proportion. 

Where  -economy  may  be  sacrificed  to  capacity,  as  where  fuel  is  very 
cheap,  it  is  customary  to  proportion  the  heating  surface  much  less  lib- 
erally. The  following  table  shows  approximately  the  relative  results 
that  may  be  expected  with  different  rates  of  evaporation,  with  anthra- 
cite coal: 

Lbs.  water  evaporated  from  and  at  212°  per  sq.ft.  heating  surface  per  hour: 
2        2.5  3         3.5  4  5  6  7          8          9         10 

Sq.ft.  heating  surface  required  per  horse-power: 
17.3      13.8       11.5         9.8         8.6         6.8         5.8         4.9      4.3      3.8      3.5 

Ratio  of  heating  to  grate  surface  if  1/3  sq.ft.  of  G.  S.  is  required  per  H.P.: 
52      41.4       34.5      29.4      25.8       20.4       17.4       13.7     12.9     11.4     10.5 

Probable  relative  economy: 
100        100          99  98  95          92          88  84        80         75         70 

Probable  temperature  of  chimney-gases,  degrees  F.: 
450        450        470        490         520         580        650         710       770      850       930 

The  relative  economy  will  vary  not  only  with  the  amount  of  heat- 
ing surface  per  horse-power,  but  with  the  efficiency  of  that  heating 
surface  as  regards  its  capacity  for  transfer  of  heat  from  the  heated 
gases  to  the  water,  which  will  depend  on  its  freedom  from  soot  and 
incrustation,  and  upon  the  circulation  of  the  water  and  the  heated 


The  efficiency  with  any  kind  of  fuel  will  depend  greatly  upon  the 
amount  of  air  supplied  to  the  furnace  in  excess  of  that  required  to 


BOILER  HORSE-POWER.  381 

support  combustion.  With  strong  draft  and  thin  fires  this  excess  may 
be  very  great,  causing  a  serious  loss  of  economy.  This  subject  has 
been  fully  discussed  in  Chapter  IX. 

With  bituminous  coal  the  efficiency  will  largely  depend  upon  the 
thoroughness  with  which  the  combustion  is  effected  in  the  furnace. 

Ratio  of  Heating  to  Grate  Surface. — In  the  early  days  of  steam 
boiler  practice,  when  boilers  of  100  II. P.  were  considered  large,  and 
the  customary  rate  of  burning  coal  was  from  8  to  10  Ibs.  per  square 
foot  of  grate  surface  per  hour,  the  ratio  of  heating  to  grate  surface  was 
considered  to  be  a  most  important  factor  in  boiler  design,  and  as  one 
writer  says,  it  was  "a  fundamental  and  almost  initial  point  of  attack 
in  the  comprehensive  subject  of  steam  power-plant  design."  It  is 
no  longer  an  "initial  point  of  attack" ;  it  is  merely  a  figure  that  may 
be  obtained,  after  the  design  is  completed,  by  dividing  the  heating 
surface  by  the  grate  surface,  if  the  figure  is  desired  for  reference  or 
comparison. 

Measurement  of  Heating  Surface. — The  usual  rule  is  to  consider 
as  heating  surface  all  the  surfaces  that  are  surrounded  by  water  on  one 
side  and  by  flame  or  heated  gases  on  the  other,  using  the  external  in- 
stead of  the  internal  diameter  of  tubes  for  greater  convenience  in  cal- 
culation, the  external  diameter  of  boiler-tubes  usually  being  made  in 
even  inches  or  half  inches.  This  method,  however,  is  inaccurate  in  the 
case  of  a  fire-tube  boiler,  for  the  true  heating  surface  of  a  fire-tube  is 
the  side  exposed  to  the  hot  gases,  i.e.,  the  inner  surface.  The  resistance 
to  the  passage  of  heat  from  the  hot  gases  on  one  side  of  a  tube  or  plate 
to  the  water  on  the  other  consists  almost  entirely  of  the  resistance  to 
the  passage  of  the  heat  from  the  gases  into  the  metal,  the  resistance  of 
the  metal  itself  and  that  of  the  wetted  surface  being  practically 
nothing.* 

RULE  for  finding  the  heating  surface  of  horizontal  tubular  boilers : 
Take  the  dimensions  in  inches.  Multiply  two-thirds  of  the  circum- 
ference of  the  shell  by  its  length;  multiply  the  sum  of  the  circum- 
ferences of  all  the  tubes  by  their  common  length ;  to  the  sum  of  these 
products  add  two-thirds  of  the  area  of  both  tube-sheets ;  from  this  sum 
subtract  twice  the  combined  area  of  all  the  tubes ;  divide  the  remainder 
by  144  to  obtain  the  result  in  square  feet. 

RULE  for  finding  the  heating  surface  of  vertical  tubular  boilers: 
Multiply  the  circumference  of  the  fire-box  (in  inches)  by  its  height 

*  See  paper  by  C,  W,  Baker,  Trans.  A.  S.  M.  E.,  vol.  xix,  p.  571. 


382  STEAM-BOILER  ECONOMY. 

above  the  grate  ;  multiply  the  combined  circumference  of  all  the  tubes 
by  their  length,  and  to  these  two  products  add  the  area  of  the  lower 
tube-sheet  ;  from  this  sum  subtract  the  area  of  all  the  tubes,  and  divide 
by  144  :  the  quotient  is  the  number  of  square  feet  of  heating  surface. 

RULE  for  finding  the  square  feet  of  heating  surface  in  tubes  :  Multi- 
ply the  number  of  tubes  by  the  diameter  of  a  tube  in  inches,  by  its 
length  in  feet,  and  by  0.2618. 

Ratio  of  Superheating  Surface  to  Boiler  Heating  Surface.  —  Power 
of  May,  1906,  publishes  three  charts,  furnished  by  R.  Ewald,  from 
Riga,  Russia,  showing  the  square  feet  of  superheating  surface  for  differ- 
ent areas  of  boiler  heating  surface  and  for  different  percentages  of 
boiler  heating  surface  situated  below  the  superheater  tubes.  They  are 
said  to  be  based  on  the  supposition  that  3.5  Ibs.  of  steam  are  generated 
per  hour  per  square  foot  of  boiler  surface,  and  the  three  charts  are  to 
be  used  respectively  for  oil  of  about  18,500  B.T.U.,  for  coal  of  about 
13,500  B.T.U.,  and  for  wood,  peat  and  similar  fuel  of  about  6000 
B.T.U.  per  Ib.  heating  value.  The  charts  are  all  straight  line 
diagrams,  corresponding  approximately  to  the  following  formulae: 

500)  P(B  +  400) 

-J.  *—  L_JL_,L. 

300) 


for  wood,  ^= 


_ 


in  which  S  =  superheating  surface,  B  =  boiler  heating  surface,  P  = 
percentage  of  the  boiler  surface  that  is  below  the  superheater  tubes. 
No  authority  or  experimental  basis  is  given  for  the  charts. 

Horse-power,  Builder's  Rating.  Heating  Surface  per  Horse-power. 
—  It  is  a  general  practice  among  builders  to  furnish  from  10  to  12 
square  feet  of  heating  surface  per  horse-power,  but  as  the  practice  is 
not  uniform,  bids  and  contracts  should  always  specify  the  amount  of 
heating  surface  to  be  furnished.  Not  less  than  one-third  square  foot 
of  grate  surface  should  ordinarily  be  furnished  per  horse-power  in  order 
that  the  boiler  may  be  able  to  develop  from  30  to  50  per  cent  more 
than  its  stated  power  for  short  periods  in  emergencies;  but  a  smaller 
proportion  may  be  sufficient  with  free-burning  coal  and  strong  draft. 
See  "Grate  Surface,"  below. 

Horse-power  of  Marine  and  Locomotive  Boilers.  —  The  term  horse- 
power is  not  generally  used  in  connection  with  boilers  in  marine 
practice,  or  with  locomotives.  The  boilers  are  designed  to  suit  the 
engines,  and  are  rated  by  extent  of  grate  and  heating  surface  only. 


BOILER  HORSE-POWER. 


383 


Grate  Surface. — The  amount  of  grate  surface  required  per  horse- 
power, and  the  proper  ratio  of  heating  surface  to  grate  surface  are 
extremely  variable,  depending  chiefly  upon  the  character  of  the  coal 
and  upon  the  rate  of  draft.  With  good  coal,  low  in  ash,  approximately 
equal  results  may  be  obtained  with  large  grate  surface  and  light  draft 
and  with  small  grate  surface  and  strong  draft,  the  total  amount  of 
coal  burned  per  hour  being  the  same  in  both  cases.  With  good 
bituminous  coal,  like  Pittsburg,  low  in  ash,  the  best  results  apparently 
are  obtained  with  strong  draft  and  high  rates  of  combustion,  provided 
the  grate  surfaces  are  cut  down  so  that  the  total  coal  burned  per 
hour  is  not  too  great  for  the  capacity  of  the  heating  surface  to  absorb 
the  heat  produced. 

With  coals  high  in  ash,  especially  if  the  ash  is  easily  fusible,  tend- 
ing to  choke  the  grates,  large  grate  surface  and  a  slow  rate  of  com- 
bustion are  required,  unless  means,  such  as  shaking  grates,  are  pro- 
vided to  get  rid  of  the  ash  as  fast' as  it  is  made. 

The  amount  of  grate  surface  required  per  horse-power  under 
various  conditions  may  be  estimated  from  the  following  table : 


Pounds   of   Coal   Burned   per   square   foot   of 

Lbs.  Water 

Lbs.  Coal 

Grate  per  hour. 

~- 

at  212°  per 
lb.  Coal. 

per  H.P. 
per  hour. 

8 

10 

12 

15 

20 

25 

30 

35     |  40 

Sq.  ft.  Grate  per  H.P. 

Good  coal 

10 

3.45 

.43 

.35 

.28 

.23 

.17 

.14 

.11 

.10 

.09 

and  boiler, 

9 

3.83 

.48 

.38 

.32 

.25 

.19 

.15 

.13 

.11 

.10 

Fair  coal  or 
boiler, 

8.61 

8 

7 

4 
4.31 
4.93 

.50 
.54 

.62 

.40 
.43 
.49 

.33 
.36 
.41 

.26 
.29 

.33 

.20 
.22 
.24 

.16 
.17 
.20 

.13 
.14 
.17 

.12 
.13 
.14 

.10 
.11 

.12 

Poor  coal  or 
boiler, 

6.9 
6 
5 

5 
5.75 
6.9 

.63 

.72 
.86 

.50 
.58 
.69 

.42 
.48 
.58 

.34 
.38 
.46 

.25 
.29 
.35 

.20 
.23 

.28 

.17 
.19 
.23 

.15 
.17 
.22 

.13 
.14 
.17 

Lignite  and 

poor  boiler. 

3.45 

10 

1.25 

1.00 

.83 

.67 

.50 

.40 

.33 

.29 

.25 

In  designing  a  boiler  for  a  given  set  of  conditions,  the  grate  surface 
should  be  made  as  liberal  as  possible,  say  sufficient  for  a  rate  of  com- 
bustion of  10  Ibs.  per  square  foot  of  grate  for  anthracite,  and  15  Ibs. 
per  square  foot  for  bituminous  coal,  and  in  practice  a  portion  of  the 
grate  surface  may  be  bricked  over  if  it  is  found  that  the  draft,  fuel, 
or  other  conditions  render  it  advisable.*  In  earlier  times,  when  plain 

*  These  figures  apply  only  to  hand  firing.  With  modern  types  of  mechanical 
stokers  with  abundant  air  supply  and  very  large  combustion  chambers,  as  much 
as  40  to  50  Ibs.  may  be  burned  per  hour  per  square  foot  of  the  horizontal  area  of 
the  furnace,  and  there  is  a  tendency  to  increase  these  amounts. 


384  STEAM-BOILER  ECONOMY. 

cylinder  and  two-flue  boilers  were  in  common  use,  it  was  customary 
to  have  a  ratio  of  say  1  to  20,  or  1  to  25,  of  grate  to  heating  surface. 
With  very  slow  rates  of  combustion  these  proportions  gave  a  fair 
degree  of  economy,  but  as  boilers  were  driven  faster,  the  economy  fell 
off,  and  the  loss  of  heat  in  the  chimney  gases  became  excessive.  This 
was  corrected  by  the  introduction  of  horizontal  tubular  boilers,  in 
which  the  grate  surface  remaining  the  same,  the  extent  of  heating 
surface  was  increased  until  the  ratio  of  grate  to  heating  surface  be- 
came 1  to  30.  When  water-tube  boilers  came  largely  into  use  it  was 
found  that  the  highest  economy  could  be  obtained  with  a  ratio  of  1 
to  40  or  1  to  50.  In  recent  years  it  has  become  quite  common  to  pile 
up  heating  surface  on  a  given  area  of  grate,  so  that  ratios  of  1  to  60 
are  not  infrequent.  The  evident  advantage  of  such  a  ratio  is  that 
it  enables  a  given  horse-power  to  be  built  on  a  smaller  ground-space 
than  before,  and  by  using  tubes  18  feet  long  instead  of  14,  and  piling 
tubes  10  or  15  rows  high  instead  of  7  or  8,  the  first  cost  of  a  given 
horse-power  is  reduced.  With  anthracite  egg  coal,  or  with  semi- 
bituminous  coal  low  in  ash,  and  with  a  strong  draft,  no  disadvantage 
results  from  this  method  of  construction;  but  with  poorer  coals,  such 
as  pea,  buckwheat,  and  rice,  and  the  bituminous  coals  of  Western 
states,  high  in  moisture,  sulphur,  and  ash,  there  is  a  most  serious 
disadvantage,  namely,  that  of  cutting  down  the  working  capacity  of 
the  boiler.  A  wrater-tube  boiler  with  2000  sq.  ft.  of  heating  sur- 
face and  40  sq.  ft.  of  grate  surface,  having  a  ratio  of  50  to  1.  and 
rated  at  200  H.P.,  may  easily  be  driven  with  semi-bituminous  or  with 
Pittsburg  coal,  the  draft  being  sufficient,  to  over  300  H.P.,  while 
with  a  poor  grade  of  Illinois  coal,  or  with  buckwheat  anthracite,  it 
would  be  difficult  to  drive  the  boiler  up  to  its  rating.  With  ordinary 
grates  and  hand-firing  with  such  coals,  increasing  the  draft  beyond 
a  certain  amount  does  not  increase  the  coal-burning  capacity,  for 
rapid  driving  only  causes  the  ash  to  accumulate  more  rapidly  and  to 
fuse  into  clinker,  choking  the  draft  through  the  coal  and  necessitating 
frequent  cleaning.  Shaking-grates  may  remedy  the  trouble  to  some 
extent,  but  the  best  remedy  is  an  increase  of  the  area  of  grate  surface 
and  a  slower  rate  of  combustion. 

In  drawing  specifications  for  bids  upon  boilers  it  is  quite  as  essen- 
tial that  the  extent  of  grate  surface  should  be  specified  as  the  extent 
of  heating  surface,  especially  when  the  coal  to  be  used  is  of  a  poor 
quality.  When  two  competing  boilermakers  offer  boilers  of  the  same 
type  and  the  same  extent  of  heating  surface,  that  one  should  be  prer 


BOILER  HORSE-POWER.  385 

ferred,  other  things  being  equal,  which  has  the  larger  grate  surface. 
It  may  be  driven  to  a  greater  capacity  than  the  other,  to  meet  emer- 
gencies, or  it  will  give  the  same  capacity  with  a  poor  grade  of  coal 
that  the  other  will  give  with  better  coal.  Too  large  a  grate  surface 
is  an  evil  that  may  easily  be  remedied,  by  shortening  the  grates,  but 
too  small  grate  surface  necessitates  the  use  of  the  higher  priced  coals, 
entails  more  labor  in  handling  fires,  more  frequent  cleaning  of  fires, 
and  consequent  loss  of  economy. 

Boilers  are  usually  sold  on  the  basis  of  rated  horse-power,  from 
10  to  12-  square  feet  of  heating  surface  being  taken  as  equivalent  to 
a  horse-power,  but  of  two  boilers,  each  of  the  same  rating  on  this 
basis,  but  one  having  say  40  sq.  ft.  of  grate  and  the  other  60,  the 
latter,  with  a  poor  grade  of  coal,  will  develop  almost  50  per  cent 
greater  power  than  the  former  and  will  give  almost  the  same  economy. 
With  a  free-burning  coal,  low  in  ash,  and  ample  draft,  the  boiler  with 
40  sq.  ft.  of  grate  may  develop  30  or  40  per  cent  above  its  rating, 
and  the  one  with  60  sq.  ft.  nearly  100  per  cent  above  rating,  but  in 
this  case,  the  boiler  with  large  grate  surface  will  show  a  great  loss 
of  economy,  because  it  is  overdriven. 

Proportions  of  Areas  of  Flues  and  other  Gas-passages. — Rules  are 
sometimes  given  making  the  area  of  gas-passages  bear  a  certain  ratio 
to  the  area  of  the  grate  surface ;  thus  a  common  rule  for  horizontal 
tubular  boilers  is  to  make  the  area  over  the  bridge  wall  \  of  the  grate 
surface,  the  flue  area  |,  and  chimney  area  |. 

For  average  conditions  with  anthracite  coal  and  moderate  draft, 
say  a  rate  of  combustion  of  12  Ibs.  coal  per  square  foot  of  grate  per 
hour,  and  a  ratio  of  heating  to  grate  surface  of  30  to  1,  this  rule  is 
as  good  as  any,  but  it  is  evident  that  if  the  draft  were  increased  so 
as  to  cause  a  rate  of  combusion  of  24  Ibs.,  requiring  the  grate  surface 
to  be  cut  down  to  a  ratio  of  60  to  1,  the  areas  of  gas-passages  should 
not  be  reduced  in  proportion.  The  amount  of  coal  burned  per  hour 
being  the  same  under  the  changed  conditions,  and  there  being  no 
reason  why  the  gases  should  travel  at  a  higher  velocity,  the  actual 
areas  of  the  passages  should  remain  as  before,  but  the  ratio  of  the 
area  to  the  grate  surface  would  in  that  case  be  doubled. 

Mi.  Barrus  states  that  the  highest  efficiency  with  anthracite  coal  is 
obtained  when  the  tube  area  is  ^  to  TV  of  the  grate  surface,  and  with 
bituminous  coal  when  it  is  J  to  y,  for  the  conditions  of  medium 
rates  of  combustion,  such  as  10  to  12  Ibs.  per  square  foot  of  grate  per 
hour,  and  12  square  feet  of  heating  surface  allowed  to  the  horse-power. 


386  STEAM-BOILER  ECONOMY. 

The  tube  area  should  be  made  large  enough  not  to  choke  the 
draft,  and  so  lessen  the  capacity  of  the  boiler;  if  made  too  large  the 
gases  are  apt  to  select  the  passages  of  least  resistance  and  escape  from 
them  at  a  high  velocity  and  high  temperature. 

This  condition  is  very  commonly  found  in  horizontal  tubular 
boilers  where  the  gases  go  chiefly  through  the  upper  rows  of  tubes ; 
sometimes  also  in  vertical  tubular  boilers,  where  the  gases  are  apt  to 
pass  most  rapidly  through  the  tubes  nearest  to  the  centre.  It  may  to 
some  extent  be  remedied  by  placing  retarders  in  those  tubes  in  which 
the  gases  travel  the  quickest. 

Air-passages  Through  Grate-bars. — The  usual  practice  is  to  make, 
the  air-opening  equal  to  30%  to  50%  of  the  area  of  the  grate;  the 
larger  the  better,  to  avoid  stoppage  of  the  air-supply  by  clinker;  but, 
with  coal  free  from  clinker,  much  smaller  air-space  may  be  used 
without  detriment.  See  "Grate-bars,"  in  Chapter  VII.  page  202. 

Performance  of  Boilers. — The  performance  of  a  steam-boiler  com- 
prises both  its  capacity  for  generating  steam  and  its  economy  of  fuel. 
Capacity  depends  upon  size,  both  of  grate  surface  and  of  heating 
surface,  upon  the  kind  of  coal  burned,  upon  the  draft,  and  also  upon 
the  economy.  Economy  of  fuel  depends  upon  the  completeness  with 
which  the  coal  is  burned  in  the  furnace,  upon  the  proper  regulation  of 
the  air-supply  to  the  amount  of  coal  burned,  and  upon  the  thorough- 
ness with  which  the  boiler  absorbs  the  heat  generated  in  the  furnace. 
The  absorption  of  heat  depends  upon  the  extent  of  heating  surface  in 
relation  to  the  amount  of  coal  burned  or  of  water  evaporated,  upon 
the  arrangement  of  the  gas-passages,  and  upon  the  cleanness  of  the 
surfaces.  The  capacity  of  a  boiler  may  increase  with  increase  of 
economy  when  this  is  due  to  more  thorough  combustion  of  the  coal 
or  to  better  regulation  of  the  air-supply,  or  it  may  increase  at  the  ex- 
pense of  economy  when  the  increased  capacity  is  due  to  overdriving, 
causing  an  increased  loss  of  heat  in  the  chimney-gases.  The  relation 
of  capacity  to  economy  is  therefore  a  complex  one,  depending  on 
many  variable  conditions. 

Many  attempts  have  been  made  to  construct  a  formula  expressing 
the  relation  between  capacity,  rate  of  driving,  or  evaporation  per 
square  foot  of  heating  surface,  to  the  economy,  or  evaporation  per 
pound  of  combustible ;  but  none  of  them  can  be  considered  satisfactory, 
since  they  made  the  economy  depend  only  on  the  rate  of  driving  (a 
few  so-called  "constants,"  however,  being  introduced  in  some  of  them 
for  different  classes  of  boilers,  kinds  of  fuel,  or  kind  of  draft),  and 


BOILER  HORSE-POWER.  387 

fail  to  take  into  consideration  the  numerous  other  conditions  upon 
which  economy  depends.  Such  formulae  are  Kankine's,  Clark's, 
Emery's,  Isherwood's,  Carpenter's,  and  Hale's.  A  discussion  of  them 
all  may  be  found  in  Mr.  E.  S.  Hale's  paper  on  "Efficiency  of  Boiler 
Heating  Surface,"  in  Trans.  Am.  Soc.  M.  E.,  vol.  xviii.  p.  328.  Mr. 
Hale?s  formula  takes  into  account  the  effect  of  radiation,  which  re- 
duces the  economy  considerably  when  the  rate  of  driving  is  less  than 
3  Ibs.  per  square  foot  of  heating  surface  per  hour.  The  author's  for- 
mula, in  which  the  efficiency  is  shown  to  be  a  function  of  six  different 
variables,  the  most  important  one  being  the  air  supply,  is  given  in  the 
chapter  on  Efficiency  of  Heating  Surface.  (Formulae  13,  14,  and  15, 
page  294.) 

For  figures  of  results  obtained  in  tests  see  Chapter  XVII. 


GHAPTEE  XII. 
"POINTS"  OF  A  GOOD  BOILER. 

THE  boilers  which  have  been  described  and  illustrated  in  Chapter 
X  include  all  the  types  which  are  extensively  used  in  land  practice  in 
the  United  States.  They  offer  enough  variety  to  satisfy  the  ideas  or 
prejudices  of  all  classes  of  purchasers.  Boilers  of  each  of  these  types, 
more  or  less  modified,  with  one  or  two  exceptions,  are  made  by  more 
than  one  builder,  the  fundamental  patents  on  all  of  them  having 
expired,  and  competition  between  rival  builders  is  so  intense  that 
any  kind  of  boiler  may  now  be  purchased  at  a  slight  advance  over 
its  cost  to  the  builder.  The  factory  cost  has  also  been  greatly  re- 
duced by  the  introduction  of  improved  machinery  and  by  the  reduced 
prices  of  raw  material.  It  would  be  out  of  place  here  to  recommend 
any  one  type  of  boiler  as  superior  to  any  other,  but  some  ideas  may 
be  given  in  regard  to  the  good  and  bad  "points"  of  boilers  in  general, 
which  may  be  of  assistance  to  an  intending  purchaser  or  an  engineer 
who  is  confused  by  the  conflicting  statements  of  rival  builders  or 
salesmen. 

Selecting  a  New  Type  of  Boiler. — The  problem  of  selecting  a  new 
form  of  boiler  to  replace  one  of  an  old  type  is,  to  the  average  steam- 
user,  one  of  considerable  difficulty  on  account  of  the  vast  variety  of 
styles  that  are  now  offered  in  the  market,  and  the  conflicting  state- 
ments of  rival  builders.  The  evolution  of  the  steam-boiler  has  now 
reached  a  period  of  extreme  confusion,  in  which  diversity  of  form  is 
the  leading  feature.  In  land  boilers  we  not  only  have  the  variety  of 
styles  shown  in  the  table  already  given  of  percentages  of  different  styles 
used  in  several  countries  of  Europe,  but  in  the  United  States  there  is 
a  continual  procession  of  new  forms  through  the  Patent  Office,  of 
which  enough  find  builders  and  advertisers  to  continually  add  to  the 
existing  confusion. 

The  claims  made  for  these  new  forms  of  boilers  are  generally  in 
inverse  ratio  to  their  merits.  The  following  are  extracts  from  adver- 
tisements in  a  single  issue  of  one  trade  journal  in  February,  1897: 

No.  1. — We  guarantee  you  a  saving  of  from  10  to  25  per  cent  with 

388 


"POINTS"  OF  A  GOOD  BOILER.  389 

equal  horse-power,  or  an  increase  of  horse-power  of  from  10  to  25  per 
cent  with  the  same  fuel  if  you  use  the steam-generator. 

No.  2. — The  circulation  positively  prevents  scale. 

No.  3. — The  best  boiler  ever  built,  combining  many  points  of  merit 
not  contained  in  any  other  boiler.  Will  evaporate  the  largest  amount 
of  water  per  pound  of  coal. 

No.  4. — Is  an  efficiency  of  30  per  cent  above  all  others  of  interest 
to  you?  Send  for  particulars. 

No.  5. — An  evaporation  of  14.66  Ibs.  of  water  from  and  at  212° 
per  pound  of  combustible. 

Such  extravagant  claims  for  new  forms  of  boilers  are  not  now  as 
common  as  they  once  were,  but  the  following  advertisement  appeared 
in  a  trade  journal  in  1914. 

Our  boilers  make  less  scale  than  boilers  of  any  other  make  because 
they  circulate  the  water  more  rapidly,  heat  it  more  uniformly  and 
cause  impurities  to  settle  in  the  mud-drum  while  water  is  yet  cool. 

It  is  worthy  of  note  that  none  of  the  large  boiler  companies,  who 
have  reputations  established  for  many  years,  advertise  in  this  manner, 
and  of  the  boilers  which  are  advertised  in  the  above  extracts,  not  one 
has  any  exceptional  merit  which  would  warrant  its  being  selected  in 
preference  to  the  best  of  the  older  and  better-known  boilers.  It  is 
simply  impossible  that  any  one  of  these  new  boilers  can,  in  an  accu- 
rate test,  evaporate  14.66  Ibs.  of  water,  from  and  at  212°  per  Ib.  of 
combustible  (if  coal  is  used  as  fuel,  it  might  do  this  and  more  with 
petroleum),  or  that  any  one  of  them  can  show  10  per  cent  better 
economy  than  a  well-proportioned  boiler  of  older  form,  or  that  any 
kind  of  circulation  can  keep  a  boiler  free  from  scale  or  from  deposits 
of  solid  matter  if  the  water  contains  scale-forming  material. 

The  moral  is  this :  Do  not  place  any  reliance  in  the  advertisement 
of  a  boiler  which  claims  that  it  is  superior  to  all  other  boilers  in  fuel- 
economy  or  in  prevention  of  scale.  The  largest  and  most  successful 
boiler  concerns,  who  make  as  good  boilers  as  have  ever  been  made, 
or  are  likely  to  be  made  for  some  years  to  come,  do  not  advertise  in 
this  way. 

Economy  of  Fuel. — Let  it  be  assumed  that  all  the  boilers  offered 
for  choice  are  built  by  makers  of  good  repute,  that  the  quality  of 
material  and  workmanship  is  beyond  question,  and  that  the  dimensions 
and  arrangement  of  all  the  parts  are  so  chosen  that  they  are  all  equally 
safe  to  resist  a  bursting  pressure.  These  essentials  of  good  boiler  con- 


390  STEAM-BOILER  ECONOMY. 

struction  may  be  secured  with  any  of  the  types  described,  by  having 
the  specifications  properly  drawn  and  by  rigid  inspection  of  the 
material  and  workmanship.  The  economy  of  fuel  which  may  be  ob- 
tained with  any  boiler  does  not  depend  upon  the  type  of  boiler,  but 
upon  its  proportions,  such  as  the  amount  of  heating  and  grate-surface 
furnished  for  a  given  horse-power,  upon  the  kind  of  furnace  used,  and 
upon  the  arrangement  of  the  gas-passages  so  as  to  cause  the  gas  to  give 
up  as  large  a  percentage  of  its  heat  as  possible  to  the  heating  surface. 
These  are  matters  of  engineering  design  with  any  type  of  boiler,  and 
any  boiler  may  have  them  so  arranged  as  to  cause  it  to  give  as  high 
an  economy  of  fuel  as  is  possible  with  any  other  boiler.  Questions 
that  arise  under  this  head  in  regard  to  any  boiler  are :  1.  Is  the  grate- 
surface  sufficient  for  burning  the  maximum  quantity  of  coal  expected 
to  be  used  at  any  time,  taking  into  consideration  the  available  draft, 
the  quality  of  the  coal,  its  percentage  of  ash,  whether  or  not  the  ash 
tends  to  run  into  clinker,  and  the  facilities,  such  as  shaking  grates, 
for  getting  rid  of  the  ash  or  clinker?  2.  Is  the  furnace  of  a  kind 
adapted  to  burn  the  particular  kind  of  coal  used?  3.  Is  the  heating 
surface  of  extent  sufficient  to  absorb  so  much  of  the  heat  generated 
that  the  gases  escaping  into  the  chimney  shall  be  reasonably  low  in 
temperature,  say  not  over  500°  F.  with  anthracite  and  600°  F.  with 
bituminous  coal?  4.  Are  the  gas-passages  so  designed  and  arranged 
as  to  compel  the  gas  to  traverse  at  a  uniform  rate  the  whole  of  the 
heating  surface,  not  being  so  large  at  any  point  as  to  allow  the  gas  to 
find  a  path  of  least  resistance  or  be  short-circuited,  or,  on  the  other 
hand,  so  contracted  at  any  point  as  to  cause  an  obstruction  to  the 
draft  ? 

These  questions  being  settled  in  favor  of  any  given  boiler,  and 
they  may  be  answered  favorably  for  boilers  of  any  of  the  modern 
types  already  described,  provided  the  furnaces  and  boilers  are  prop- 
erly designed,  the  relative  merits  of  the  different  types  may  now  be 
considered  with  reference  to  their  danger  of  explosion;  their  probable 
durability;  the  character  and  extent  of  repairs  that  may  be  needed 
from  time  to  time,  and  the  difficulty,  delay,  and  expense  that  these 
may  entail;  the  accessibility  of  every  part  of  the  boiler  to  inspection, 
internal  and  external ;  the  facility  for  removal  of  mud  and  scale  from 
every  portion  of -the  inner  surface,  and  of  dust  and  soot  from  the 
exterior ;  the  water-  and  steam-capacity ;  the  steadiness  of  water-level ; 
and  the  arrangements  for  securing  dry  steam. 

Each  one  of  the  points  above  referred  to   should  be  considered 


"POINTS"  OF  A  GOOD  BOILER.  391 

carefully  by  the  intending  purchaser  of  any  type  of  boiler  with  which 
he  is  not  familiar  by  experience.  The  several  points  may  be  con- 
sidered more  in  detail. 

Danger  of  Explosion. — All  boilers  may  be  exploded  by  over-press- 
ure, such  as  might  be  caused  by  the  combination  of  an  inattentive 
fireman  and  an  inoperative  safety-valve,  or  by  corrosion  weakening 
the  boiler  to  such  an  extent  as  to  make  it  unable  to  resist  the  regular 
working  pressure;  but  some  boilers  are  much  more  liable  to  explosion 
than  others.    In  considering  the  probability  of  explosion  of  any  boiler 
of  recent  design,  it  is  well  to  study  it  to  discover  whether  or  not  it  has 
any  of  the  features  which  are  known  to  be  dangerous  in  the  plain 
cylinder,  the  horizontal  tubular,  the  vertical  tubular  and  the  locomo- 
tive boilers.     The  plain  cylinder  boiler  is  liable  to  explosion  from 
strains  induced  by  its  method  of  suspension,  and  by  changes  of  tem- 
perature.   Alternate  expansion  and  contraction  may  produce  a  line  of 
weakness  in  one  of  the  rings,  which  may  finally  cause  an  explosion. 
A  boiler  should  be  so  suspended  that  all  its  parts  are  free  to  change 
their  position  under  changes  of  temperature  without  straining  any 
part.    The  circulation  of  water  in  the  boiler  should  be  sufficient  to  keep 
all  parts  at  nearly  the  same  temperature.     Cold  feed-water  should 
not  be  allowed  to  come  in  contact  with  the  shell,  as  this  will  cause 
contraction  and  strain.     The  horizontal  tubular  boiler,  and  all  ex- 
ternally-fired shell  boilers,  are  liable  to  explosion  from  overheating 
of  the  shell;  due  to  accumulation  of  mud,  scale  or  grease  on  the  por- 
tion of  the  shell  lying  directly  over  the  fire;  to  a  double  thickness 
of  iron,  as  at  a  lap-joint,  together  with  some  scale,  over  the  fire;  or 
to  low  water  uncovering  and  exposing  an  unwetted  part  of  the  shell 
directly  to  the  hot  gases.     Vertical  tubular  boilers  are  liable  to  ex- 
plosion from  deposits  of  mud,  scale  or  grease  upon  the  lower  tube- 
sheet,  and  from  low  water  allowing  the  upper  part  of  the  tubes  to 
get  hot  and  cease  to  act  as  stays  to  the  upper  tube-sheet.  Locomotive 
boilers  may  explode  from  deposits  on  the  crown-sheet,  from  low  water 
exposing  the  dry  crown-sheet  to  the  hot  gases,  and  from  corrosion 
of  the  stay-bolts.    Double-cylinder  boilers,  such  as  the  French  elephant 
boiler,  and  the  boilers  used  at  some  American  blast-furnaces,  have 
exploded  on  account  of  the  formation  of  a  "steam-pocket"  on  the 
upper  portion  of  the  lower  cylinder,  the  steam  being  prevented  from 
escaping  by  the  lap-joint  of  one  of  the  rings,  thus  making  a  layer 
of  steam  about  %  incn  tnick  against  the  shell  which  was  directly 
exposed  to  the  hot  gases. 


392  STEAM-BOILER  ECONOMY. 

The  above-mentioned  are  only  a  few  of  the  causes  of  explosions, 
but  they  are  the  principal  ones  that  are  due  to  features  of  design. 
These  features  should  be  looked  for  in  any  new  style  of  boiler,  and  if 
they  are  found  they  should  be  considered  elements  of  danger.  Such 
questions  as  the  following  may  be  asked:  Is  the  method  of  suspen- 
sion of  the  boiler  such  as  to  allow  its  parts  to  be  free  to  move  under 
changes  of  temperature?  Is  the  circulation  such  as  to  keep  all  parts 
at  practically  the  same  temperature?  Is  there  a  shell  with  riveted 
seams  exposed  to  the  fire?  Is  there  a  shell  exposed  to  the  fire  which 
may  at  any  time  be  uncovered  by  water  or  be  covered  with  scale  ?  Is 
there  a  crown-sheet  on  which  scale  may  lodge?  Are  there  sufficient 
facilities  for  the  removal  of  scale?  Are  there  vertical  or  inclined 
tubes  acting  as  stays  to  an  upper  sheet,  the  upper  part  of  which  tubes 
may  become  overheated  in  case  of  low  water?  Are  there  any  stayed 
sheets,  the  stays  of  which  are  liable  to  become  corroded  ?  Is  there  any 
chance  for  a  steam-pocket  to  be  formed  on  a  sheet  which  is  exposed 
to  the  fire? 

In  addition  to  the  above-mentioned  features  of  design,  which  are 
elements  of  danger,  all  boilers,  as  already  stated,  are  liable  to  explosion 
due  to  corrosion.  Internal  corrosion  is  usually  due  to  acid  feed-water, 
or  to  very  pure  feed-water  containing  dissolved  air,  and  all  boilers 
are  equally  liable  to  it.  External  corrosion,  however,  is  more  liable 
to  take  place  in  some  designs  of  boilers  than  in  others,  and  in  some 
locations  rather  than  in  others.  If  any  portion  of  a  boiler  is  in  a 
cold  and  damp  place,  it  is  liable  to  rust  out.  For  this  reason  the  mud- 
drums  of  many  modern  forms  of  boilers  are  made  of  cast  iron,  which 
resists  rusting  better  than  either  wrought  iron  or  steel.  If  any  part 
of  a  boiler,  other  than  a  part  made  of  cast  iron,  is  liable  to  be  exposed 
to  a  cold  and  damp  atmosphere,  or  covered  with  damp  soot  or  ashes, 
or  exposed  to  drip  from  rain  or.  from  leaky  pipes,  and  especially  if  such 
part  is  hidden  by  brickwork  or  otherwise  so  that  it  cannot  be  in- 
spected, that  part  is  an  element  of  danger. 

Durability. — The  question  of  durability  is  partly  covered  by  that 
of  danger  of  explosion,  which  has  already  been  discussed,  but  it  also  is 
related  to  the  question  of  incrustation  or  scale.  The  plates  and 
tubes  of  a  boiler  may  be  destroyed  by  internal  or  external  corrosion, 
but  they  may  also  be  burned  out.  It  may  be  regarded  as  impossible 
to  burn  a  plate  or  tube1  of  iron  or  steel,  no  matter  how  high  the  tem- 
perature of  the  flame,  provided  one  side  of  the  metal  is  covered  with 
water.  If  a  steam-pocket  is  formed,  so  that  the  water  does  not  touch 


"POINTS"  OF  A   GOOD  BOILER.  393 

the  metal,  of  if  there  is  a  layer  of  grease  or  hard  scale,  then  the  plate 
or  tube  may  be  burned.  In  a  water- tube  which  is  horizontal,  or 
nearly  so,  and  in  which  the  circulation  of  water  is  defective,  it  is  pos- 
sible to  form  a  mass  of  steam  which  will  drive  the  water  away  from 
the  metal,  and  thus  allow  the  tube  to  burn  out.  In  considering  the 
probable  durability  of  a  boiler,  we  may  ask  the  same  questions  as  those 
that  have  been  asked  concerning  danger  of  explosion.  There  are, 
however,  many  chances  of  burning  out  a  minor  part  of  a  boiler  with- 
out serious  danger,  to  one  chance  of  a  disastrous  explosion.  Thus 
the  tubes  of  a  water-tube  boiler,  if  allowed  to  become  thickly  covered 
with  scale,  might  be  burned  out  without  causing  any  further  destruc- 
tion than  the  rupture  of  a  single  tube.  A  new  type  of  boiler  should 
be  questioned  in  regard  to  the  likelihood  of  frequent  small  repairs 
being  necessary,  and  as  well  in  regard  to  its  liability  to  complete 
destruction.  We  may  ask:  Is  the  circulation  through  all  parts  of 
the  boiler  such  that  the  water  cannot  be  driven  out  of  any  tube  or 
from  any  portion  of  a  plate,  so  as  to  form  a  steam-pocket  exposed  to 
high  temperature  ?  Are  there  proper  facilities  for  removing  the  scale 
from  every  portion  of  the  plates  and  tubess? 

Repairs. — The  questions  of  durability  and  of  repairs  are,  in  some 
respects,  related  to  each  other.  The  more  infrequent  and  the  less 
extensive  the  repairs,,  the  greater  the  durability.  The  tubes  of  a  boiler, 
where  corroded  or  burnt  out,  may  be  replaced,  and  made  as  good  as 
new.  The  shell,  when  it  springs  a  leak,  may  be  patched,  and  is  then 
likely  to  be  far  from  as  good  as  new.  When  the  shell  corrodes  badly 
it,  must  be  replaced,  and  to  replace  the  shell  is  the  same  as  getting  a 
new  boiler.  Herein  is  one  advantage  of  the  sectional  water-tube 
boilers.  The  sections,  or  parts  of  a  section,  may  be  renewed  easily, 
and  made  good  as  new,  while  the  shell,  being  far  removed  from  the 
fire  and  easily  kept  dry  externally,  is  not  liable  either  to  burning  out 
or  external  corrosion.  In  considering  the  merits  of  a  new  style  of 
boiler,  with  reference  to  repairs,  we  may  ask  what  parts  of  the  boiler 
are  most  likely  to  give  out  and  need  to  be  repaired  or  replaced  ?  Are 
these  repairs  easily  effected ;  how  long  will  they  require ;  and  after 
they  are  made  is  the  boiler  as  good  as  new?  If  a  new  style  of  boiler 
made  up  of  special  parts  not  procurable  except  from  its  builder,  the 
question  may  be  asked :  How  long  is  the  builder  likely  to  remain  in 
business  and  be  able  to  furnish  these  .special  parts? 

Facility  for  Removal  of  Scale  and  for  Inspection. — These  questions 
have  already  been  discussed  to  some  extent  under  the  head  of  dura- 


394  STEAM-BOILER  ECONOMY. 

bility.  Some  water- tube  boilers,  now  dead  and  gone,  were  some  years 
ago  put  on  the  market,  which  had  no  facilities  for  the  removal  of 
scale.  It  was  claimed  by  their  promoters  that  they  did  not  need  any, 
because  their  circulation  was  so  rapid.  Every  few  years  boilers  of 
these  types  are  re-invented,  and  the  same  claim  is  made  for  them,  that 
their  rapid  circulation  prevents  the  formation  of  scale.  The  fact  is 
that  if  there  is  scale-forming  material  in  the  water  it  will  be  de- 
posited when  the  water  is  evaporated,  and  no  amount  or  kind  or  circu- 
lation will  keep  it  from  accumulating  on  every  part  of  the  boiler  and 
in  every  kind  of  tubes,  vertical,  horizontal,  and  inclined.  The  nearly 
vertical  circulating  tubes  of  a  water-tube  boiler,  in  which  the  circula- 
tion is  nine  times  as  fast  as  the  average  circulation  in  the  inclined 
tubes,  sometimes  have  been  found  nearly  full  of  scale;  that  is,  a 
4-inch  tube  had  an  opening  in  it  of  less  than  1  inch  diameter.  This 
was  due  to  carelessness  in  blowing  off  the  boiler,  or  exceptionally  bad 
feed-water,  or  both.  If  circulation  would  prevent  scaling  at  all,  it 
would  prevent  it  here. 

Water-  and  Steam-capacity. — It  is  claimed  for  some  forms  of 
boilers  that  they  are  better  than  others  because  they  have  a  larger 
water-  or  steam-capacity.  Great  water-capacity  is  useful  where  the 
demands  for  steam  are  extremely  fluctuating,  as  in  a  rolling-mill  or  a 
sugar  refinery,  where  it  is  desirable  to  store  up  heat  in  the  water  in  the 
boilers  during  the  periods  of  the  least  demand,  to  be  given  out  during 
periods  of  greatest  demand.  Large  water-capacity  is  objectionable  in 
boilers  for  factories,  usually,  especially  if  they  do  not  run  at  night, 
and  the  boilers  are  cooled  down,  because  there  is  a  large  quantity  of 
water  to  be  heated  before  starting  each  morning.  If  "rapid  steam- 
ing" or  the  ability  to  get  up  steam  quickly  from  cold  water,  or  to 
raise  the  pressure  quickly,  is  desired,  large  water-capacity  is  a  detri- 
ment. The  advantage  of  large  steam-capacity  is  usually  overrated. 
It  is  useful  to  enable  the  steam  to  be  drained  from  water  before  it 
escapes  into  the  steam-pipe,  but  the  same  result  can  be  effected  by 
means  of  a  dry  pipe,  as  in  locomotive  and  marine  practice,  in  which 
the  steam-space  in  the  boiler  is  very  small  in  proportion  to  the  horse- 
power. Large  steam-space  in  the  boiler  is  of  no  importance  for 
storing  energy  or  equalizing  the  pressure  during  the  stroke  of  an 
engine.  The  water  in  the  boiler  is  the  place  to  store  heat,  and  if  the 
steam-pipe  leading  to  an  engine  is  of  such  small  capacity  that  it  re- 
duces the  pressure  at  the  engine,  the  remedy  is  a  steam-reservoir  close 
to  the  engine  or  a  large  steam-pipe. 


"POINTS"  OF  A   GOOD  BOILER.  395 

Water  Space  and  Steam  Space. — The  sizes  of  the  water  space  and 
the  steam  space  of  a  steam  boiler  have  no  necessary  relation  to  either 
its  capacity  or  its  economy.  A  small  water  space  will  cause  a  boiler 
to  be  a  "rapid  steamer;"  that  is,  it  will  generate  steam  in  a  short 
time  after  a  fire  is  started  in  the  furnace,  and  rate  of  generation  of 
steam  will  vary  with  every  change  of  condition  of  the  fire  and  of  the 
draft.  Steam  fire-engines  have  boilers  with  very  small  water  spaces. 
Large  water  spaces  act  as  reservoirs  of  heat,  and  they  tend  to  cause 
the  boiler  to  steam  steadily,  although  the  conditions  of  the  fire  may 
vary.  They  are  of  special  value  when  the  engine  load  is  a  fluctuating 
one,  as  in  rolling-mills,  electric  street  railway  service,  etc. 

The  extent  of  steam  space  is  rather  an  accident  of  the  shape 
of  the  boiler  than  an  element  in  its  design.  A  study  of  the  amount 
of  steam  space  per  rated  horse-power  in  different  styles  of  boilers, 
by  S.  Q.  Hayes  (Power,  Sept.,  1894),  gives  the  following  figures: 
Locomotive,  0.141  sq.  ft. ;  Harrison  safety,  0.196 ;  vertical  tubular, 
0.320  to  0.665;  water  tube  safety,  0.336  to  0.906;  horizontal  return 
tubular,  0.752  to  0.985;  two-flue,  1.51  to  1.92;  and  plain  cylindrical 
boilers,  2.50  sq.  ft. 

Steadiness  of  Water-level. — This  requires  either  a  large  area  of 
water-surface  and  volume  of  water,  so  that  the  level  may  be  changed 
slowly  by  fluctuations  in  the  demand  for  steam  or  in  the  delivery  of 
the  feed-pump,  or  else  constant,  and  preferably  automatic,  regula- 
tion of  the  feed-water  supply  to  suit  the  steam  demand.  A  rapidly 
lowering  water-level  is  apt  to  expose  dry  sheets  or  tubes  to  the  action 
of  the  hot  gases,  and  thus  be  a  source  of  danger.  A  rapidly  rising 
level  may,  before  it  is  seen  by  the  fireman,  cause  water  to  be  carried 
over  into  the  steam-pipe,  and  endanger  the  engine. 

Large  area  of  water-surface  alone  is  not  always  sufficient  to  insure 
steadiness  of  water-level.  Sudden  fluctuations  in  the  activity  of  the 
fire,  such  as  take  place  when  the  gases  from  freshly-fired  soft  coal 
burst  into  flame,  are  apt  to  cause  a  sudden  rise  in  the  water-level. 
For  this  reason,  boilers  with  horizontal  water-  and  steam-drums, 
whether  fire-tube  or  water-tube  boilers,  should  preferably  have  drums 
not  less  than  30  ins.  diameter,  so  that  the  water-level  may  be  allowed 
to  vary  5  or  6  ins.  from  its  normal  position  without,  on  the  one  hand, 
endangering  the  burning  out  of  the  tubes,  or,  on  the  other,  of  making 
wet  steam. 

Dryness  of  Steam. — Most  of  the  modern  forms  of  both  fire-tube 
and  water-tube  boilers  give  practically  dry  steam,  that  is,  steam  con- 


396  STEAM-BOILER  ECONOMY. 


taining  not  over  1J%  of  moisture,  when  the  water-level  is  not 
allowed  to  rise  more  than  5  or  6  ins.  above  its  mean  position,  even 
when  driven  as  much  as  100%  beyond  their  rated  capacity;  but 
boilers  with  vertical  tubes,  with  small  water-level  area,  are  apt,  some- 
times, to  have  the  water-level  fluctuate  violently,  and  they  require  to 
be  provided  with  superheating  surface  and  dry  pipes,  or  steam  sep- 
arators, in  order  to  insure  dry  steam.  Alkaline  feed-water  is  often 
a  cause  of  "foaming,"  causing  wet  steam. 

Water-circulation.  —  Positive  and  complete  circulation  of  the  water 
in  a  boiler  is  important  for  two  reasons  :  (  1  )  To  keep  all  parts  of  the 
boiler  of  a  uniform  temperature,  and  (2)  to  prevent  the  adhesion  of 
steam-bubbles  to  the  surface,  which  may  cause  overheating  of  the 
metal.  It  is  claimed  by  some  manufacturers  that  the  rapid  circula- 
tion -of  water  in  their  boilers  tends  to  make  them  more  economical 
than  others.  We  have  as  yet,  however,  to  find  any  proof  that  increased 
rapidity  of  circulation  of  water  beyond  that  usually  found  in  any 
boiler  will  give  increased  economy.  We  know  that  increased  rate 
of  flow  of  air  over  radiating  surfaces  increases  the  amount  of  heat 
transmitted  through  the  surface,  but  this  is  because  by  the  increased 
circulation  cold  air  is  continually  brought  in  contact  with  the  surface, 
making  an  increased  difference  of  temperature  on  the  two  sides,  which 
causes  increased  transmission.  But  by  increasing  the  rapidity  of  cir- 
culation in  a  steam-boiler  we  cannot  vary  the  difference  of  tempera- 
ture to  any  appreciable  extent,  for  the  water  and  the  steam  in  the 
boiler  are  at  about  the  same  temperature  throughout.  The  ordinary 
or  "Scotch"  form  of  marine  boiler  shows  an  exception  to  the  general 
rule  of  uniformity  of  temperature  of  water  throughout  the  boiler, 
but  the  temperature  above  the  level  of  the  lower  fire-tubes  is  practi- 
cally uniform. 


CHAPTER  XIII 
BOILER  DESIGN  AND  CONSTRUCTION. 

Boiler  and  Boiler  Plant  Design. — Steam-boiler  design  may  be 
divided  into  two  parts:  1,  general  or  plant  design,  that  is  the  deter- 
mination of  the  kind,  number,  size  and  arrangement  of  boilers  re- 
quired to  produce  a  given  amount  of  steam  in  a  stated  time,  the  total 
area  of  grate  surface,  the  kind  of  furnace  or  stoker  to  be  used ;  and,  2, 
detail  design,  relating  to  the  construction  of  an  individual  boiler  after 
its  general  shape  and  size  have  been  determined. 

The  consulting  engineer  or  the  engineer  of  a  power  plant  is  usually 
concerned  only  with  the  first  of  these  two  branches  of  the  general  sub- 
ject of  boiler  design;  he  leaves  to  the  engineer  of  the  boiler  maker 
the  details  of  the  manufacture  of  the  boiler  itself,  except  in  so  far 
as  he  compares  the  specifications  offered  by  each  boiler  maker  with 
the  requirements  named  in  his  general  specifications  and  with  gov- 
ernmental rules  and  regulations  and  the  rules  of  boiler  insurance 
companies.  Occasionally  a  consulting  .engineer  is  called  on  to  make 
an  original  design  of  a  boiler,  but  not  often:  the  usual  rule  is  to 
accept  the  standard  design  of  boilers  that  are  in  the  market. 

In  preparing  to  make  a  design  for  a  boiler  plant  for  any  given 
service  the  following  data  should  be  known,  at  least  approximately: 

a.  The  nature  of  the  demand  for  steam,  whether  steady  or  fluctu- 
ating. 

1.  If  steady,  as  in  a  cotton  mill,  the  number  of  pounds  of 

water  to  be  evaporated  per  hour  when  the  mill  is  run- 
ning at  its   full   capacity. 

2.  If  fluctuating,  as  in  an  electric  power  and  lighting  plant, 

or  a  central  station  heating  plant,  charts  showing  the 
steam  demand   for   each   hour   of   a   day   in  seasons   of 
heaviest  and  of  lightest  demand. 
5.  The  quality  and  price  of  coal  or  other  fuel. 

c.  The  quality  of  the  feed  water. 

d.  The  temperature  of  the  feed  water. 

e.  The  maximum  pressure  of  steam  to  be  carried. 

397 


398  STEAM-BOILER  ECONOMY. 

From  the  data  d  and  e  the  factor  of  evaporation  is  calculated, 
which,  multiplied  by  the  pounds  of  water  per  hour,  from  data  a,  1 
and  2,  gives  the  equivalent  evaporation  per  hour  from  and  at  212° . 

For  a  steady  demand,  as  in  1,  it  will  usually  be  found  most  profit- 
able to  install  sufficient  heating  surface  so  that  the  boilers  will  not 
have  to  be  driven  at  a  rate  higher  than  their  normal  rating  of  10 
sq.  ft.  of  heating  surface  per  boiler  horse-power,  or  3.45  Ibs.  of  water 
evaporated  from  and  at  212°  per  sq.  ft.  of  heating  surface  per  hour. 

With  loads  that  have  a  high  peak,  lasting  but  4  to  8  hours  out 
of  the  24,  as  in  2,  a  great  saving  in  first  cost  of  boilers  and  of  real 
estate  may  be  made  by  allowing  the  boilers  to  be  driven  during  the 
peak  of  the  load  at  from  2  to  3  times  their  normal  rating,  but  in 
that  case  it  will  be  necessary  both  to  install  mechanical  stokers  and 
to  control  the  firing  by  analyses  of  the  gases,  in  order  to  avoid  ex- 
cessive waste  of  fuel  by  overdriving,  such  as  is  shown  by  the  diagrams 
of  efficiency  given  in  Chapter  IX. 

In  all  cases  provision  must  be  made  for  one,  or  in  large  power 
plants  more  than  one,  of  the  boilers  to  be  out  of  service  for  cleaning 
or  repairs. 

Having  determined  the  amount  of  heating  surface  required  the 
next  question  to  be  settled  is  the  amount  of  grate  surface.  This 
depends  on  several  considerations : 

1.  The  cost  of  real  estate.     If  it  is  very  costly,  as  in  large  cities, 
it  may  be  advisable  to  use  relatively  small  grate  surface  and  to  burn 
the  coal  at  a  high  rate  during  the  heavy  load,  say  25  to  50  Ibs.  of 
coal  per  sq.  ft.  of  grate  surface  per  hour,  but  this  requires  special 
facilities  for  getting  rid  of  ash  and  clinker,  such  as  shaking  grates 
or  mechanical  stokers,  very  large  combustion  chambers,  to  allow  of 
the  gases  being  burned  before  they  reach  the  heating  surfaces,  and 
high  chimneys,  150  ft.  or  over,  or  forced  draft.    In  some  large  plants 
it  has  been  found  advisable,  on  account  of  the  expense  of  ground  space 
to  locate  the  boilers  on  two  or  three  floors  of  the  boiler  house.    Where 
real  estate  is  not  expensive  it  is  desirable  to  proportion  the  grate 
surface  liberally,  so  as  to  require  the  burning  of  say  from  10  to  20  Ibs. 
of  coal  per  sq.  ft.  of  grate  per  hour,  especially  for  small  plants  with 
moderate  heights  of  chimney  and  hand  firing. 

2.  The  quality  and  price  of  fuel  that  is  available.     These  will 
govern  to  a  large  extent  the  size  of  the  grate  surface  and  the  volume 
of  combustion  space  to  be  provided.     With  Western  bituminous  coals 
and  lignites,  and  wood,  bagasse,  tan  bark  and  the  like,  the  grate  sur- 


BOILER  DESIGN  AND  CONSTRUCTION.  399 

face  and  the  combustion  chamber  require  to  be  much  larger  than 
with  semi-bituminous  or  Eastern  bituminous  coals.  With  anthracite 
of  small  size,  high  in  ash,  very  large  grate  surfaces  are  needed,  but 
on  account  of  the  small  proportion  of  volatile  matter  large  combus- 
tion chambers  are  not  necessary.  With  oil  fuel  no  grate  surface  is 
needed,  but  the  combustion  chamber  must  be  large  for  high  rates  of 
driving,  in  order  that  the  fuel  may  be  burned  without  smoke  and 
with  good  economy. 

The  total  amount  of  heating  surface  and  grate  surface  having  been 
decided  upon,  a  selection  of  the  type  of  boiler  suitable  for  all  the 
conditions,  including  the  kind  of  feed- water,  may  now  be  made  from 
the  various  types  in  the  market,  after  a  careful  consideration  of  the 
"Points  of  a  Good  Boiler"  described  in  Chapter  XII,  and  general 
specifications  may  now  be  sent  to  the  most  reliable  manufacturers 
asking  for  bids  and  detailed  specifications  for  boilers  of  the  total 
heating  surface  and  grate  surface  required,  the  boilers  to  carry  the 
maximum  stated  pressure  with  a  factor  of  safety  of  not  less  than  5, 
and  to  occupy  not  more  than  the  total  ground  area  of  the  size  and 
shape  given,  including  in  this  area  sufficient  room  for  passages  be- 
tween batteries  or  groups  of  boilers,  for  firing  space,  for  storage  of 
a  given  quantity  of  coal,  and  space  for  removal  of  tubes  and  for 
access  to  the  rear  of  the  boilers. 

The  size  of  the  individual  boilers  in  a  plant  requires  some  con- 
sideration. For  many  years  boilers  of  500  to  600  H.P.  (5000  to 
6000  sq.  ft.  of  heating  surface)  have  been  most  common  in  large 
plants,  but  there  is  a  tendency  to  use  much  larger  boilers,  1000  to 
2000  H.P.  and  upwards,  the  advantages  being  a  saving  in  ground 
space  and  in  brick-work,  and  a  possible  saving  of  fuel  due  to  more 
perfect  control  of  furnace  conditions  by  analyses  of  the  gases  and 
of  labor,  due  to  there  being  fewer  furnaces  to  be  attended  to.  With 
these  large  boilers  automatic  feeding  of  coal  from  overhead  storage 
bins  is  essential. 

Modern  Boiler  Plants. — In  the  most  recent  large  power  plants  no 
expense  has  been  spared  in  the  installation  of  machinery  to  handle 
both  coal  and  ashes,  thereby  reducing  the  labor  cost,  and  also  to 
provide  very  large  combustion  spaces,  to  enable  the  volatile  gases  to  be 
completely  burned  before  they  reach  the  heating  surface  of  the  boilers 
even  at  the  maximum  rate  of  driving.  In  consequence  a  cross-sectional 
view  through  the  boiler  house  shows  that  the  greater  portion  of  its 
space  is  taken  for  coal-  and  ash-storage,  for  room  for  railroad  cars  to 


400 


STEAM-BOILER  ECONOMY. 


FIG.  141. — SECTION  THROUGH  ONE-HALF  OF  A  LARGE  BOILER  PLANT. 


BOILER  DESIGN  AND  CONSTRUCTION. 


401 


deliver  coal  and  receive  ash,  elevators  for  handling  the  material,  and 
for  combustion  spaces,  flues  and  chimney.  Illustrations  of  two  boiler 
plants  showing  these  features  are  shown  below. 

A  Large  Boiler  Plant  in  France. — Power,  Jan.  31,  1911,  describes 
the  St.  Denis  station  of  the  Electrical  Society  of  Paris.  Fig.  141 
shows  a  section  through  one-half  of  the  boiler  house.  The  boilers, 
17  in  all,  are  of  the  marine  Babcock  &  Wilcox  type,  provided  with 
very  long  chain-grate  stokers,  the  front  half  of  which  are  roofed 
over,  large  combustion  chambers,  superheaters  and  Green  economizers. 
It  will  be  noticed  that  in  this,  as  in  all  large  modern  power  plants 
the  space  occupied  by  the  boilers  themselves  is  but  a  small  fraction 
of  the  total  space  in  the  boiler  house.  Each  boiler  has  4520  sq.  ft. 
of  heating  surface,  147  sq.  ft.  grate  surface;  ratio  30.8  to  1;  1215 
sq.  ft.  superheater  surface  and  1600  sq.  ft.  economizer  surface.  The 
boilers  are  guaranteed  to  deliver  4  Ibs.  of  steam,  superheated  to  662 °F., 
per  sq.  ft.  of  heating  surface  per  hour,  with  capacity  for  25%  increase, 
or  5  Ibs.,  without  difficulty,  with  an  efficiency  of  80%,  including  the 
economizers,  when  evaporating  at  the  rate  of  3.7  to  3.9  Ibs.  of  steam 
per  hour  per  sq.  ft.  of  boiler  surface,  at  662°  F.,  the  feed-water 
temperature  being  68°  F.  This  evaporation,  taking  the  higher 
figures,  is  equivalent  to  5  Ibs.  from  and  at  212°  per  sq.  ft.  of  boiler 
heating  surface  per  hour.  An  8-hour  test  of  5  boilers  made  in  1908, 
with  Scotch  coal  containing  by  analysis  33.6  volatile  matter,  7.6 
moisture,  7.3  ash,  gave  an  equivalent  evaporation  from  and  at  212° 
of  5.93  Ibs.  per  sq.  ft.  of  heating  surface  per  hour,  and  an  efficiency 
of  83.3%,  including  the  economizer.  Some  of  the  other  data  are 
as  follows: 


Deg.  F. 

B.T.U. 
above  32°. 

Diff. 

Temperature  of 

water  entering  economizer.  . 

105.8 

73.7 

'  '      leaving  economizer.  .  . 

200.1 

168.0 

94 

steam  entering  superheater. 

381.2 

1198 

1030 

'  '      leaving  superheater  .  . 

579.2 

1307 

109 

gases  entering  economizer  .  . 

534.2 

'  '     leaving  economizer  .  .  . 

327.2 

Steam  pressure 

185  Ibs.  gage.     CO2  in  gases. 

12% 

The  efficiency  of  the  boiler  and  superheater,  omitting  the  econ- 
omizer was  83.3  X  1139-4-1233  =  77%.  The  gain  due  to  the  econ- 
omizer was  94  -r- 1139  =7.6%. 


402 


STEAM-BOILER  ECONOMY. 


The  Northwest  Station  of  the  Commonwealth  Edison  Co., 
Chicago.  (Power,  April  29,  1913). — The  plans  provide  for  two 
separate  groups  of  buildings,  as  a  precaution  against  complete  inter- 
ruption of  service  by  an  accident,  each  group  consisting  of  a  generator 
house,  a  boiler  house,  and  a  low  building  containing  transformers, 
bus  bars,  and  switches.  Each  generator  house  is  planned  for  six 
20,000  KW.  Curtis  turbine  generators,  and  each  turbine  is  served 


FIG.  142. — PLAN  OF  LARGE  ELECTRIC  POWER  PLANT. 

by  its  own  group  of  10  boilers,  each  of  5800  sq.  ft.  of  heating  sur- 
face and  capable  of  generating  economically  30,000  Ibs.  of  steam  per 
hour.  Each  group  of  boilers  is  ample  to  supply  its  generator  under 
maximum  load,  allowing  one  boiler  to  be  out  of  service  for  cleaning 
or  repairs.  Fig.  143  shows  a  cross  section  through  one  of  the  groups 
of  10  boilers  and  through  the  coal-handling  space  serving  two  oppo- 
site groups. 

The  boilers  are  set  with  a  high  combustion  chamber.  The  coal 
is  burned  on  Babcock  &  Wilcox  chain  grates,  which  have  an  area 
of  115  sq.  ft.,  giving  a  ratio  of  grate  surface  to  heating  surface  of 
1  to  50.4.  Steam  is  generated  at  250  Ibs.  pressure  and  superheated 


BOILER  DESIGN  AND  CONSTRUCTION.  403 

125°  F.  Each  group  of  boilers  is  served  by  its  own  steel  stack, 
250  ft.  high,  above  the  boiler-room  floor.,  by  17  ft.  inside  diameter. 

A  separate  coal-handling  system  is  employed  for  each  two  groups 
of  boilers.  Coal  either  direct  from  the-  mine  or  from  storage  piles 
is  run  into  the  boiler  house  in  cars  at  grade  level  underneath  the 
fire-room  floor,  which  is  some  22  ft.  above  the  ground  line.  The 
two  tracks^  bring  the  cars  over  a  reinforced-concrete  hopper  and 
thus  the  dumping  type  of  car  can  be  unloaded  into  the  hopper  direct. 
The  non-dumping  cars  are  unloaded  by  a  traveling  crane  and  a 
2-cu.  yd.  clam-shell  bucket  which  drops  the  coal  through  an  opening 
provided  between  the  tracks.  From  the  receiving  hopper  the  coal 
is  fed  into  a  traveling  crusher  which  runs  on  tracks  over  the  34x3  6-in. 
buckets  of  a  conveyor.  The  conveyor  raises  the  coal  and  deposits 
it  in  overhead  bunkers  located  over  the  firing  aisle,  as  shown,  and 
from  these  it  is  fed  through  spouts  to  the  stoker  hoppers. 

The  fine  coal  which  sifts  through  the  grates  falls  through  spouts 
back  into  the  receiving  hopper  and  is  again  raised  to  the  overhead 
bunkers  by  the  conveyor.  The  ashes  falling  off  the  end  of  the  chain 
grates  are  caught  in  ash  hoppers  below,  which  have  a  capacity  for 
one  day's  accumulation.  Railroad  cars  for  receiving  the  ashes  are 
run  in  under  the  hoppers  and  the  latter  are  emptied  once  each  day. 

Designing  Boilers  for  a  Small  Street-railway  Plant.* — In  entering 
upon  the  studies  preliminary  to  the  design  of  the  steam-boilers  for 
a  small  or  medium-sized  electrical  street-railway  power-plant  the 
engineer  must  take  into  consideration  some  peculiar  features  of  the 
service  required  from  the  boilers  which  differ  more  or  less  from  those 
which  govern  the  design  of  boilers  for  other  purposes,  such  as  a 
factory.  Such  features  are:  the  extreme  variations  of  the  load  upon 
the  engines  from  hour  to  hour,  and  the  consequent  variation  in  the 
quantity  of  steam  to  be  furnished;  the  prime  necessity  of  having  the 
boiler-plant  constantly  in  condition  to  furnish  the  maximum  amount 
of  steam  required  during  the  hours  of  heaviest  load;  the  absence  of 
holidays  or  slack  seasons  during  which  general  repairs  or  alterations 
may  be  made;  and  the  considerable  uncertainty  that  exists  before 
the  plant  is  put  in  operation  concerning  the  actual  amount  of  power 
that  may  be  required  and  the  probable  additions  that  may  be  needed 
as  the  road  is  extended  or  as  traffic  increases.  The  first  considerations, 
therefore,  in  the  design  of  the  boiler-plant  are  certainty  of  operation 
under  the  severest  load,  and  capacity  for  furnishing  the  maximum 
amount  of  steam  that  may  be  needed  under  the  most  adverse  con- 
ditions, such  as  a  combination  of  heaviest  load,  bad  weather,  poor 

*  From  an  article  by  the  author  in  Street  Railway  Review,  February,  1899. 


404 


STEAM-BOILER  ECONOMY. 


FIG.  143. — BOILER  PLANT  OF  COMMONWEALTH  EDISON  Co.,  CHICAGO. 


BOILER  DESIGN  AND   CONSTRUCTION. 


405 


coal,  and  a  portion  of  the  boiler-plant  being  laid  off  for  cleaning  or 
repairs. 

To  meet  these  requirements  it  is  necessary  not  only  to  have  the 
boilers  of  sufficient  capacity  to  meet  the  greatest  demand  for  steam, 
but  also  to  have  enough  boilers  to  allow  one  of  them  to  be  laid  off 
without  curtailing  the  steam-supply  below  the  maximum  quantity 
that  may  at  any  time  be  required  by  the  engines.  In  even  the 
smallest-sized  plant  it  is  advisable  to  have  not  less  than  three  boilers, 
any  two  of  which  are  able  to  run  the  plant  at  the  time  of  heaviest 
loading.  In  larger  plants,  four,  five,  or  more  boilers  may  be  installed, 
and  so  arranged  that  any  one  of  them  may  be  laid  off  at  any  time  for 


13       8       4        0        8       10      12 

Ncoa 


4        6       8       10      12 

FIG.  144.  —  LOAD-DIAGRAM  OF  A  STREET-RAILWAY  PLANT. 


cleaning  or  repairs  without  interfering  with  the  operation  of  the 
others. 

Assuming  that  the  boiler-plant  is  to  contain  one  boiler  more  than 
is  sufficient  to  generate  the  steam  required  under  the  conditions  of 
maximum  load,  the  poorest  coal  being  supplied  that  is  ever  expected 
to  be  used  at  the  station,  and  the  weather  the  most  unfavorable  as 
regards  the  draft  and  the  amount  of  moisture  in  the  air  and  in  the 
coal,  "we  proceed  to  consider  the  number,  size,  proportions,  and  style 
of  the  boilers  to  be  selected. 

The  boiler-plant  is  usually  one  of  the  last  of  the  divisions  of  the 
complete  power-plant  that  are  to  be  designed.  Before  designing  it 
we  must  know  the  maximum  quantity  of  steam  that  will  be  needed. 
The  electrical  engineer  of  the  railway  company  will  furnish  data  as 
to  the  electrical  horse-power  that  will  be  required  from  the  dynamos: 
and  he  will  hand  to  the  steam  -engineer  a  diagram  something  like  the' 
one  shown  in  the  accompanying  cut,  Fig.  144,  giving  the  heaviest 
loads  expected  on  the  dynamos  during  twenty-four  hours.  From 
these  data  the  steam-engines  or  turbines  will  be  selected,  involving 


406  STEAM-BOILER  ECONOMY. 

a  study  of  their  size  and  of  their  probable  steam-consumption  at  dif- 
ferent loads.  The  two  "peaks'"'  of  the  load-diagram  will  be  carefully 
considered,  and  the  question  will  be  decided  whether  these  peaks  are 
to  be  taken  care  of  by  storage-batteries,  by  overloading  the  engines 
or  dynamos,  or  by  the  use  of  a  separate  engine  and  dynamo  to  be 
operated  during  three  or  four  hours  of  the  day  when  the  load  is 
heaviest. 

The  steam-engine  questions  being  decided,  a  careful  calculation  is 
then  made  of  the  probable  steam  consumption  per  hour  during  the 
single  hour  or  fraction  of  an  hour  of  maximum  load.  Not  until  this 
question  is  settled  is  it  time  to  prepare  the  design  of  the  boiler-plant. 

The  boilers,  after  one  of  them  is  reserved  for  cleaning  or  repairs, 
must  be  capable  of  furnishing  sufficient  steam  to  the  engines  during 
the  time  of  the  peak  of  the  load,  even  when  the  coal  is  poor  and  the 
weather  bad,  and  the  engine  not  in  its  best  condition  as  to  steam- 
tightness  and  valve-adjustment;  and  to  this  consideration  every  other 
one,  such  as  first  cost  of  boilers,  or  economy  of  coal,  must  be  made 
secondary. 

The  maximum  number  of  pounds  of  steam  per  hour  now  being 
given,  and  the  pressure  of  steam  required  by  the  engines  and  the 
probable  feed-water  temperature  being  known,  we  have  the  data  with 
which  to  begin  figuring  on  the  boilers.  By  referring  to  a  table  of 
"factors  of  evaporation,"  we  may  reduce  this  number  to  the  equivalent 
number  of  pounds  per  hour  evaporated  "from  and  at  212°  F." 
Dividing  this  by  34^  gives  the  number  of  "boiler  horse-power."  A 
slight  allowance,  say  1  per  cent,  may  be  added  to  cover  loss  of  heat 
due  to  radiation  from  the  steam-pipes. 

'Having  the  amount  of  work  to  be  done  by  the  boilers  during  the 
time  of  the  peak  of  the  load,  we  now  consider  how  this  capacity  is  to 
be  obtained.  The  first  essential  in  a  boiler  is  a  furnace  with  capacity 
for  burning  enough  coal.  We  must  therefore  proportion  the  furnace 
before  we  proportion  the  boiler,  and  to  do  this  we  must  first  find  out 
how  many  pounds  of  coal  are  to  be  burned  per  hour  during  the  time 
of  maximum  steam  demand.  This  is  rather  a  complex  question,  for 
it  involves  many  variable  elements,  such  as  the  quality  of  the  coal,  the 
kind  of  furnace,  the  rate  of  driving  of  the  boiler,  and  the  skill  of  the 
firemen. 

The  number  of  pounds  of  coal  required  per  hour  will  be  equal  to 
the  quotient  obtained  by  dividing  the  equivalent  evaporation  from 
and  at  212°  per  hour,  in  pounds,  by  the  number  of  pounds  of  water 
that  may  be  evaporated  from  and  at  212°  by  1  Ib.  of  coal.  This  latter 
number  will  vary  anywhere  from  12,  when  the  best  grade  of  semi- 
bituminous  coal,  low  in  ash,  is  used,  in  a  furnace  adapted  to  burn  all 
the  volatile  part  of  the  coal,  with  a  boiler  so  proportioned  as  to  be 
capable  of  absorbing  75  per  cent  of  the  heat  generated  in  the  furnace, 
and  with  skilful  firing,  down  to  5  Ibs.  or  less,  with  a  poor  grade  of 
western  bituminous  coal,  high  in  moisture,  ash,  and  sulphur,  burned 


BOILER  DESIGN  AND  CONSTRUCTION.  407 

in  an  ordinary  furnace  directly  under  the  boiler,  with  no  provision 
for  burning  the  volatile  matter  or  preventing  smoke,  with  a  boiler 
having  insufficient  heating  surface,  and  therefore  overdriven,  and  with 
unskilful  firing.  With  lignite,  or  lignitic  coal,  from  Utah,  a  figure 
as  low  as  3.79  Ibs.  has  been  obtained.  (Trans.  A.  S.  M.  E.,  vol.  iv. 
p.  263).  The  writer  once  obtained  as  low  as  5.09  Ibs.  from  a  poor 
quality  of  Illinois  coal,  with  expert  firing,  with  the  boiler  driven  16 
per  cent  below  its  rating,  but  with  both  the  furnace  and  the  grate- 
bars  unsuited  to  the  coal.  (Trans.  A.  S.  M.  E.,  vol.  iv.  p.  267.) 

It  may  be  estimated  that  with  any  kind  of  coal  the  evaporation 
per  pound  of  coal  will  be  in  the  neighborhood  of  15  per  cent  less  with 
a  rate  of  driving  of  6  Ibs.  of  water  from  and  at  212°  per  square  foot 
of  heating  surface  per  hour  than  at  a  rate  of  3  Ibs.,  the  rate  for  maxi- 
mum economy.  [This  is  for  hand-fired  boilers  in  ordinary  operation, 
With  mechanical  stokers  and  the  firing  regulated  in  accordance  with 
the  results  of  gas  analyses  the  loss  due  to  driving  at  the  higher  rate 
may  be  reduced  to  6  or  7  per  cent.] 

Extent  of  Heating  Surface  Required. — For  factory  boilers,  or  for 
any  boilers  that  are  to  be  driven  at  a  uniform  rate  throughout  the 
day,  the  boilers  should  be  so  proportioned  that  the  rate  of  driving 
should  not  exceed  3  Ibs.  of  water  from  and  at  212°  per  square  foot  of 
heating  surface  per  hour;  the  extra  cost  of  coal  for  driving  at  a  more 
rapid  rate  usually  being  greater  than  the  interest  on  the  extra  invest- 
ment necessary  to  secure  a  sufficient  extent  of  heating  surface  over 
and  above  that  required  for  more  rapid  rates  of  driving. 

With  boilers  for  electric  street-railway  service,  however,  the  case 
is  entirely  different.  The  heavy  load  upon  the  boiler-plant  lasts  for 
only  about  four  hours  out  of  the  twenty-four,  and  unless  money  is  very 
cheap  and  coal  very  dear,  it  will  usually  pay  to  sacrifice  say  15  per 
cent  of  economy  during  those  four  hours  rather  than  go  to  the  expense 
necessary  to  proportion  the  boilers  so  that  they  will  be  driven  at  their 
most  economical  rate  during  those  four  hours.  It  is  also  to  be  con- 
sidered that  the  extra  boiler  which  is  to  be  put  in  the  plant  so  that 
any  one  boiler  may  at  any  time  be  laid  off  for  cleaning  or  repairs  may 
be  used  most  of  the  time,  since  repairs  and  cleaning  are  not  required 
often,  so  that  all  the  boilers  may  be  in  service  during  the  time  of  the 
peak  of  the  load  for  a  large  proportion  of  the  days  of  the  year,  and 
the  excessive  rate  of  driving  during  the  time  of  the  peak  of  the  load 
may  thus  be  diminished. 

It  will  therefore  not  be  bad  designing  if  the  extent  of  heating 
surface  is  proportioned  so  as  to  allow  of  the  boilers,  after  one  is  laid 
off  for  cleaning  or  repairs,  to  be  driven  at  a  rate  of  6  Ibs.  of  water 
evaporated  from  and  at  212°  per  square  foot  of  heating  surface  per 
hour  during  the  time  of  the  peak  of  the  load,  and  sufficient  coal- 
burning  capacity  is  provided  in  the  furnaces,  so  that  enough  coal  may 
be  burned,  including  the  15  per  cent  wasted  by  rapid  driving,  to 
evaporate  this  amount  under  the  most  unfavorable  conditions  of  wet 


408  STEAM-BOILER  ECONOMY. 

weather  and  of  poor  coal.  [In  the  most  modern  practice  with  under- 
feed stokers,  boilers  are  sometimes  driven  during  peak  loads  at  a  rate 
as  high  as  10  Ibs.  of  water  from  and  at  212°  per  sq.  ft.  per  hour.] 

Assume  that  the  steam  engineer's  estimates  show  that  600  I.H.P. 
will  be  required  to  be  furnished  by  the  engines  during  the  time  of 
maximum  load,  that  the  engines  are  non-condensing,  requiring  30  Ibs. 
of  steam  per  I.H.P.  per  hour  at  their  economical  load  and  20  per  cent 
more  when  overloaded  so  as  to  furnish  the  600  I.H.P.;  that  the 
feed-water  is  furnished  from  a  heater  at  200°  P.,  and  that  the  steam- 
pressure  is  125  Ibs.,  we  then  make  a  calculation  as  follows : 

600    I.H.P. 
30    Ibs.  steam  per  I.H.P.  per  hour. 

18,000    Ibs.  per  hour. 
Add 3,600    20  per  cent  for  overloaded  engines. 

21,600    Ibs.  per  hour. 
Mult.  by.  . .    1.056     factor  of  evaporation  for  feed  at  200°  and  steam  of  125  Ibs. 

Product  .  .  .22,810    Ibs.  equivalent  evaporation  from  and  at  212°  per  hour. 
Divide  by.  .          6     Ibs.  evaporation  per  square  foot  heating  surface  per  hour. 

Quotient .  .  .   3,802     square  feet  heating  surface. 

This  is  the  very  smallest  amount  of  heating  surface  that  should 
be  provided  for  the  given  conditions.  It  may  be  divided  among  two 
boilers  of  not  less  than  1901  sq.  ft.  each,  or  three  boilers  of  1267  sq. 
ft.  each,  and  in  either  case  an  additional  boiler  of  the  same  size  must 
be  provided  so  that  one  boiler  may  be  laid  off.  The  plant  will  there- 
fore contain  either  three  boilers  of  1901  sq.  ft.  each  =  5703  sq.  ft., 
or  four  boilers  of  1267  sq.  ft.  each  =  5068  sq.  ft.  It  may  be  found 
that  the  three  larger  boilers  including  setting,  valves,  piping,  etc.,  will 
cost  little  if  any  more  than  the  four  smaller  boilers  with  their  setting, 
etc.,  and  it  may  also  be  considered  advisable  to  have  the  three  larger 
boilers,  with  their  greater  total  extent  of  heating  surface,  to  provide 
against  the  contingency  of  an  increased  amount  of  steam  being  needed 
by  the  engines. 

A  plant  of  three  boilers  is  a  favorite  arrangement  for  a  new  street- 
railway  plant,  two  of  the  boilers  being  set  in  one  battery  and  the  third 
singly,  a  space  being  left  alongside  of  the  third  boiler  for  a  fourth, 
completing  two  batteries,  if  .ever  it  should  be  needed. 

Now  let  us  assume  that  the  coal  to  be  used  is  a  rather  low  grade 
of  Illinois  coal,  of  a  heating  value  of  14,300  heat-units  per  pound  of 
combustible,  and  that  it  may  be  expected  to  contain  occasionally  as 
high  as  18  per  cent  ash  and  12  per  cent  moisture.  The  heating  value 
per  pound  of  coal  will  then  be  14,300  X  0.70  =  10,010  heat-units. 
This  divided  by  970.4  gives  10.32  Ibs.  of  water  from  and  at  212°  as 
the  possible  evaporation  of  the  coal  if  it  were  completely  burned  and 
all  the  heat  utilized  by  the  boiler.  But  only  a  portion  can  be  utilized, 


BOILER  DESIGN  AND  CONSTRUCTION 


409 


say  55  per  cent,  if  the  boiler  is  provided  only  with  an  ordinary  setting, 
or  say  65  per  cent  if  it  is  set  with  a  fire-brick  oven,  especially  designed 
to  burn  the  volatile  gases,  or  if  it  is  provided  with  a  down-draft  furnace 
or  a  mechanical  stoker  suitable  for  that  grade  of  coal.  The  difference 
in  economy  between  an  efficiency  of  55  per  cent  and  one  of  65  per 
cent  is  not  10  per  cent,  as  some  may  suppose,  but  10-f-  65  =  15.4  per 
cent. 

We  now  make  the  following  calculation : 


Plain 
Furnace. 

Special 
Furnace. 

Heating  value  of  1  Ib.  of  coal,  equivalent  evaporation  from 
and  at  212° 

10  32 

10  32 

Efficiency  of  boiler  and  furnace                

55 

65 

Product,  Ibs.  from  and  at  212°  
Deduct  15  per  cent  for  loss  due  to  driving  the  boiler  at  6  Ibs. 
per  sq.  ft.  of  heating  surface  per  hour,  or  double  its  most 
economical  rate  

5.676 
851 

6.708 
1.006 

Lbs.  water  evaporated  from  and  at  212°  per  Ib.  of  coal  
Divide  these  figures  into  the  figure  already  found  for  total 
water  from  and  at  212°  per  hour 

4.825 
22,810 

5.702 
22810 

Quotient,  Ibs.  of  coal  per  hour      .          

4,727 

4,000 

The  difference,  727  Ibs.,  is  15.4  per  cent  of  4727  Ibs.,  which  agrees 
with  the  economy  of  the  more  efficient  furnace  as  above  stated  and 
checks  the  computation. 

Extent  of  Grate-surface  Required. — To  calculate  the  extent  of 
grate-surface  required  we  must  know  how  many  pounds  of  coal  may 
be  burned  per  square  foot  of  grate  per  hour.  This  will  depend  on  the 
draft,  on  the  kind  of  grate  used,  and  on  the  nature  of  the  coal  as  to 
free-burning  quality  and  as  to  its  clinkering  on  the  grates  and  choking 
the  air-supply.-  We  may  assume  that  a  chimney  150  ft.  high  is  pro- 
vided, which  after  making  allowances  for  bends  in  the  flues  from  the 
boiler  to  the  chimney  will,  under  the  most  unfavorable  conditions  of 
weather,  give  a  draft  of  at  least  0.5  in.  of  water-column  at  the  end  of 
the  boiler.  The  coal  is  free-burning,  and  will  burn  rapidly  if  supplied 
with  enough  air  through  the  grate-bars,  but  it  clinkers  badly.  With 
ordinary  grates  we  cannot  count  on  burning  it  at  a  faster  rate  than 
25  Ibs.  per  sq.  ft.  of  grate  per  hour,  but  with  shaking  grates  well 
handled,  so  as  to  keep  the  fire  clear  of  clinker,  a  rate  of  35  Ibs.  may  be 
expected.  We  now  calculate  the  grate-surface  required  as  follows: 


Plain 
Furnace. 

Special. 
Furnace. 

Coal  to  be  burned  per  hour,  Ibs 

4727 

4000 

Plain  grates,  25  Ibs.  per  hour,  sq.  ft  .  . 

190 

160 

Shaking  grates,  35  Ibs.  per  hour,  sq.  ft 

135 

114 

410 


STEAM-BOILER  ECONOMY. 


With  shaking  grates  and  hard,  steady  firing,  we  may  expect  a  loss 
through  the  grates  of  unburned  coal  amounting  to  about  2  per  cent 
more  than  the  loss  through  the  plain  grates,  but  as  in  a  street-railway 
plant  this  hard  firing  will  last  only  about  two  hours  a  day,  we  need 
make  no  change  in  our  calculation  on  this  account. 

We  thus  have  four  different  figures  for  the  extent  of  grate-surface 
required,  according  to  whether  we  use  ordinary  or  special  furnaces 
and  ordinary  or  shaking  grates.  Dividing  the  heating  surface  already 
found,  3802,  by  these  figures,  we  have  for  the  ratio  of  heating  to  grate- 
surface  the  following: 


Plain  Furnace. 

Special  Furnace. 

Plain 
Grate. 

Shaking 
Grate. 

Plain 
Grate. 

Shaking 
Grate. 

Sq.  ft.  of  grate 

190 
20.1 

135 

28.2 

160 

23.8 

114 

33.3 

Ratio-  heating  to  grate-surface  

These  figures  for  the  ratio  of  heating  to  grate-surface  are  very 
much  smaller  than  those  provided  in  the  common  designs  of  modern 
boilers,  especially  those  of  the  water-tube  type.  The  ratio  they  give 
usually  ranges  from  35  to  50.  The  reason  for  this  difference  is  that 
the  data  upon  which  the  above  calculations  are  based  are  very  different 
from  those  upon  which  these  boilers  are  designed.  We  have  assumed 
a  maximum  rate  of  driving  of  6  Ibs.  of  water  evaporated  from  and  at 
212°  per  square  foot  of  heating  surface  per  hour,  with  an  intentional 
sacrifice  of  economy  in  order  to  save  first  cost  of  installation.  We 
have  also  assumed  a  low  grade  of  coal  that  clinkers  on  the  grate,  and 
in  the  case  of  the  plain  furnace  a  low  efficiency.  In  the  design  of  the 
ordinary  water-tube  boiler,  especially  for  factory  purposes,  economy 
of  coal  is  the  first  consideration.  The  heating  surface  is  therefore 
made  of  such  an  extent  that  it  does  not  require  to  be  driven  at  a  rate 
greater  than  3  Ibs.  per  sq.  ft.  per  hour  on  an  average,  with  a  maximum 
of  4  or  4  J  Ibs.  The  boilers  are  by  most  builders  rated  in  H.P.  at  the 
rate  of  3.45  Ibs.  evaporation  per  square  foot  of  heating  surface  per 
hour,  or  10  sq.  ft.  per  H.P.,  and  when  evaporation  tests  are  made  to 
prove  guarantees  a  good  quality  of  coal  is  usually  obtained  and  the 
boilers  are  driven  at  not  above  4  Ibs.  per  sq.  ft.  of  heating  surface  per 
hour. 

Another  reason  for  the  high  ratios  of  heating  to  grate-surface  in 
modern  water-tube  boilers  is  that  when  designed  with  a  view  to 
economy  of  first  cost  and  of  ground-space  occupied  they  are  made 
long,  narrow,  and  high,  so  as  to  pile  a  great  amount  of  heating  surface 
on  a  small  ground  area.  A  narrow  boiler  means  a  narrow  grate- 
surface,  and  as  it  is  not  easy  for  a  fireman  to  handle  with  good  results 
a  grate  over  7  ft.  long,  it  means  limited  extent  of  grate-surface.  This 
is  all  right  for  good  semi -bituminous  coal  or  for  Pittsburg  or  Hocking 


BOILER  DESIGN  AND  CONSTRUCTION.  411 

Valley  bituminous,  which  are  both  free-burning  and  low  in  ash.  With 
these  coals  and  strong  draft  and  a  ratio  of  heating  to  grate-surface  of 
45  or  even  50  to  1,  it  is  possible  to  drive  the  boiler  to  double  its 
economical  rate.  For  poor  coals,  however,  whether  anthracite  or  bitu- 
minous, such  a  ratio  gives  entirely  too  small  a  grate  for  rapid  driving. 

In  the  year  1896,  in  a  series  of  tests  made  by  the  writer  on  a 
water-tube  boiler  with  a  very  poor  quality  of  Illinois  coal,  with  an 
ordinary  furnace  and  plain  grate-bars,  and  with  a  good  draft,  he  found 
that  only  about  85  per  cent  of  the  capacity  of  the  boiler  could  be 
developed  even  with  expert  firing.  The  chief  troubles  were  the 
elinkering  of  the  grates  and  the  excessive  amount  of  moisture  in  the 
coal,  which  retarded  the  combustion.  With  the  same  boiler  provided 
with  a  fire-brick  arch  setting,  with  shaking  grates,  and  with  Hocking 
\Talley  lump  coal  the  boiler  was  driven  to  over  170  per  cent  of  its 
rating,  or  over  5.1  Ibs.  of  water  evaporated  from  and  at  212°  per  square 
foot  of  heating  surface  per  hour.  Had  it  been  possible  to  double  the 
extent  of  grate-surface  when  using  the  poor  grade  of  coal  it  is  quite 
likely  that  the  capacity  obtained  could  have  been  doubled. 

Having  made  the  calculation,  as  above  shown,  for  the  extent  of 
grate-surface  required  under  the  four  assumed  conditions,  we  must 
next  consider  which  one  of  the  four  results  should  be  adopted  in  the 
design.  Unless  coal  is  very  cheap  it  will  pay  to  go  to  any  reasonable 
expense  to  provide  the  special  furnace,  either  a  fire-brick  oven  built 
in  front  of  the  boiler  with  arrangements  for  burning  the  smoky  gases, 
or  a  down-draft  furnace,  or  a  mechanical  stoker.  With  any  of  these 
devices  a  saving  of  15  per  cent  in  fuel  should"  be  expected  when  the 
coal  is  a  highly  volatile  bituminous.  Shaking  grates  are  also  desirable 
in  a  street-railway  plant  using  poor  fuel,  since  they  enable  the  grate 
to  be  kept  free  from  clinker,  and  diminish  greatly  the  grate-surface 
and  therefore  the  ground  area  required. 

Specifications  for  Bids. — Having  fixed  upon  the  extent  of  grate- 
surface  that  is  necessary  to  burn  the  coal  under  the  most  unfavorable 
conditions  of  weather,  moisture,  etc.,  for  the  heaviest  load,  adding,  of 
course,  the  grate-surface  for  the  extra  or  reserve  boiler,  this  should  be 
entered  in  the  specifications  for  bidders  for  boilers,  and  no  bid  should 
be  considered  which  did  not  give  the  full  extent  called  for.  Many 
expensive  mistakes  have  been  made  by  purchasers  of  boilers  who  have 
accepted  the  guarantees  of  economy  and  capacity  offered  by  builders, 
without  reference  to  the  extent  of  grate-surface.  After  erection  the 
boilers  may  be  proved  to  have  fulfilled  the  guarantees,  on  an  expert 
test,  with  good  coal,  but  afterwards  they  fail  to  develop  the  additional 
capacity  required  of  them  in  emergencies,  or  even  their  rated  capacity 
when  the  coal  is  poorer  than  that  used  in  the  test.  The  remedy  then 
usually  is  the  costly  one  of  obtaining  additional  boilers,  and  sometimes 
of  building  a  new  boiler-house.  The  purchaser  is  fortunate  if  he  can, 
by  a  change  in  the  style  of  furnace  or  of  grates,  or  by  building  a  taller 
chimney  or  by  introducing  forced  draft,  so  increase  the  capacity  of 
the  boilers  as  to  avoid  the  necessity  of  buying  additional  ones. 


412  STEAM-BOILER  ECONOMY. 

The  extent  of  heating  surface  found  by  the  calculation  should  also 
be  entered  in  the  specifications  as  the  minimum  to  be  bidden  upon. 
Some  bidders  may  not  be  able  to  furnish  together  with  the  specified 
extent  of  grate-surface  as  small  an  extent  of  heating  surface  as  that 
called  for,  since  their  designs  are  not  adapted  for  such  small  ratios  of 
heating  to  grate-surface  as  those  given  above,  but  there  is  no  objection 
to  their  furnishing  as  much  more  as  they  choose,  and  among  bidders 
offering  the  same  grate-surface  those  offering  the  greater  extent  of 
heating  surface  should  have  the  preference,  other  conditions  being 
equal.  Capacity  for  emergencies  being  obtained  by  extent  of  grate- 
surface,  economy  of  coal  will  be  obtained  by  extent  of  heating  surface 
above  that  needed  to  give  an  evaporation  at  the  rate  of  6  Ibs.  .per  sq. 
ft.  of  heating  surface  per  hour. 

Bidders  Guarantees. — Guarantees  of  economy  and  capacity  may 
be  inserted  in  specifications,  but  they  should  be  considered  secondary 
as  compared  with  dimensions  of  grate  and  heating  surface,  and  nd 
attention  should  be  paid  to  guarantees  of  unusual  economy  offered  by 
any  bidder  who  does  not  give  any  more  heating  surface  than  other 
bidders,  unless  that  guarantee  is  based  upon  the  offer  of  a  special 
furnace  or  stoker,  which  may  reasonably  be  expected  to  give  better 
economy  than  a  plain  furnace  when  soft  coal  is  used. 

Type  of  Boiler. — The  calculations  made  as  above  described  are 
.applicable  to  any  type  of  boiler.  The  selection  of  a  type  depends  on 
other  considerations  than  capacity  or  economy,  for  these  depend  upon 
proportions  and  not  on  type.  These  considerations  are  safety,  dura- 
bility, convenience,  or  facility  for  cleaning  and  making  repairs,  ground 
space  occupied,  ability  to  furnish  dry  steam  when  overdriven,  and 
last  of  all,  cost. 

Materials  Used  in  Boilers. — For  the  shells,  tubes,  rivets  and  braces 
the  material  now  in  almost  universal  use  is  a  special  kind  of  soft 
open-hearth  steel,  low  in  sulphur  and  phosphorus  and  of  a  tensile 
strength  not  exceeding  65,000  Ibs.  per  sq.  in.  for  shell  plates  and  not 
exceeding  55,000  Ibs.  per  sq.  in.  for  rivets.  Prior  to  the  year  1890 
steel  of  higher  tensile  strength  had  frequently  been  used,  but  it 
often  proved  too  brittle  to  withstand  the  severe  strains  of  service 
due  not  onl}r  to  internal  pressure  but  also  to  alternate  heating  and 
cooling.  Before  the  general  introduction  of  steel  for  boiler  plates 
(1875  to  1885),  a  special  grade  of  wrought  iron  known  as  "C.H. 
No.  1"  (charcoal  hammered)  was  the  favorite  material.  Wrought 
iron  is  still  used  to  some  extent  for  tubes3  rivets  and  braces,  but 
its  use  is  relatively  decreasing. 

Cast  iron  is  used  for  fire-doors,  grate-bars,  manhole  and  hand- 
hole  plates,  headers  of  water-tube  boilers  (for  pressures  under  160 
lb.),  mud  drums  (not  exceeding  18  in.  diameter),  and  nozzles  for 


BOTLER  DESIGN  AND  CONSTRUCTION. 


413 


pipe   attachments,   but   there   is   a  tendency   to   substitute   rolled   or 
forged  steel  for  all  these  purposes  except  grate  bars. 

Quality  of  Steel.  (Massachusetts  Boiler  Rules,  1910.)  Open- 
hearth  Process. — All  plates  and  rivets  used  in  the  construction  of  steel 
shells  or  drums  of  boilers  shall  bo  as  specified  by  the  American  Society 
for  Testing  Materials,  1901. 


' 

Flange  or  Boiler 
Steel. 

Fire-box 
Steel. 

Extra  Soft 
Steel. 

Phosphorus,  not  to  exceed,  acid 
Phosphorus,  not  to  exceed,  basic 
Sulphur,  not  to  exceed. 

0.06% 
0.04% 
0.05% 
0.30  to  0.60 
55,000  to  65,000 
HT.S. 
36% 

0.04% 
0.03% 
0.04% 
0.30  to  0.50 
52,000  to  62,000 

HT.S, 

26% 

0.04% 
0.04% 
0.04 
0.30  to  0.50 
45,000  to  55,000 
^T.S. 
28% 

Manganese 

Tensile  strength,  Ibs.  per  sq.in. 
Yield  point,  not  less  than  
Elongation  in  8  in.  not  less  than 

Steel  for  rivets  shall  be  of  the  extra  soft  class. 

For  each  increase  of  |  in.  in  thickness  above  f  in.  a  deduction  of 
1%,  and  for  each  decrease  of  ^  in.  in  thickness  below  ^  in.  a  de- 
duction of  2J  per  cent  shall  be  made  from  the  specified  elongation. 

The  report  of  the  A.  S.  M.  E.  Boiler  Code  Committee,  1914,  ap- 
proved by  the  American  Boiler  Manufacturers'  Association,  contains 
the  following : 

The  steel  shall  conform  to  the  following  requirements: 


FLANGE 


r.    i 
Carbon 


FIREBOX 

/  Plate  %  in.  thick    and  under .  .  0.12 — 0.25% 
in.  thick 


Manganese 

0.30  —  0.60% 

0.30  —  0 

50% 

Phosphorus  {£cjc 
Sulphur  

.  .  .Not  over  0.05% 
.  .  .  Not  over  0.05% 

Not  over 
Not  over 
Not  over 

0.04% 
0.035% 
0.04% 

Copper. 

Not  over 

005% 

Tensile  strength,  Ib. 

per  SQ.  in 

55  000  —  65  000 

55  000  —  63  000 

Yield  point,  min.,  It 

).  per  sq.  in  . 

0  5  tens  str 

0  5  tens  str 

Elongation  in  8-in., 

min.,  per  cent  

1,500,000 

1,500,000 

Tens.  str. 


Tens.  str. 


For  material  over  %  in.  in  thickness  a  deduction  of  0.5  from  the  percentage  of 
elongation  shall  be  made  for  each  increase  of  y%  in.  in  thickness  above  %  in.,  to  a 
minimum  of  20  per  cent. 

Fig.  145  shows  the  correct  form  for  test  specimens.  The  old  form, 
Fig.  146,  which  makes  the  tensile  strength  from  10%  to  25%  too 


414  STEAM-BOILER  ECONOMY. 

high,  used  by  the  IT.  S.  Supervising  Inspectors  for  many  years,  is  now 
abandoned. 


3 

^ 

?Ol 

JHfi) 

r\ 

-3  to  ( 

FIG.  145. — SHAPE  OF  TEST-PIECE.         FIG.  146. — INCORRECT  TEST-PIECE. 

Bending  tests. — The  test  specimen  shall  be  1J  in.  wide,  if  pos- 
sible, and  of  the  same  thickness  as  the  plate  from  which  it  is  cut,  but 
for  material  more  than  f  in.  thick  the  specimen  may  be  J  in.  thick. 
Both  before  and  after  quenching  the  specimen  shall  bend  cold  180° 
flat  on  itself  without  fracture  on  the  outside  of  the  bent  portion. 
The  cold  bending  test  shall  be  made  on  the  material  in  the  condition 
in  which  it  is  to  be  used,  and  prior  to  the  quenched  bending  test 
it  shall  be  heated  to  a  light  cherry  red,  as  seen  in  the  dark,  and 
quenched  in  water  of  a  temperature  between  80°  and  90°  F.  For 
fire-box  steel  the  homogeneity  test  of  the  Penn.  E.  R.  specifications 
is  made  (see  M.  E.  Pocket-book,  8th  ed.  p.  484). 

Plates  are  to  be  stamped  with  the  heat  number,  brand  and  lowest 
tensile  strength,  and  name  and  location  of  manufacturer,  as  directed 
by  the  rules.  Plates  will  be  considered  up  to  gage  if  measuring  not 
over  0.01  inch  less  than  the  ordered  gage. 

Cast  steel  used  in  any  part  of  boilers  or  superheaters  shall  have 
not  less  than  50,000  Ibs.,  and  cast  iron  used  in  boilers  not  less  than 
18,000  Ibs.  per  square  inch  tensile  strength. 

Cross  pipes  connecting  steam  and  water  drums  and  mud  drums  of 
water-tube  boilers  shall  be  of  wrought  or  cast  steel  when  the  working 
pressure  exceeds  160  Ibs.  per  sq.  in. 

Pressure  parts  of  superheaters,  attached  to  boilers  or  separately 
fired,  shall  be  of  wrought  or  cast  steel  when  the  working  pressure 
exceed  50  Ibs.  per  sq.  in. 

Boiler  and  superheater  mountings,  such  as  nozzles,  cross  pipes, 
steam  pipes,  fittings,  valves  and  their  bonnets  shall  be  of  wrought 
or  cast  steel  when  exposed  to  steam  which  is  superheated  over  80° 
F.  Water-leg  and  door-frame  rings  of  vertical  fire-tube  boilers 
36  in.  or  over  in  diameter,  or  of  locomotive  boilers,  shall  be  of  wrought 
or  cast  steel,  or  wrought  iron. 

E.  D.  Meier,  president  of  the  Heine  Safety  Boiler  Co.,  comment- 
ing on  these  specifications  in  1912,*  says: 

Such  steel  can  safely  be  depended  on  with  a  factor  of  safety  of 
five,  (some  laws  allow  four). 

Sulphur  makes  iron  and  steel  "red  short,"  i.  e.,  brittle  at  red 

*  Stevens  Institute  Indicator,  Oct.,  1912. 


BOILER  DESIGN  AND  CONSTRUCTION.  415 

heat.  Phosphorus  makes  them  "cold  short/'  i.  e.,  brittle  at  low 
temperatures.  .Both  in  excess  would  endanger  the  work  while  flang- 
ing, bending,  or  modeling  when  hot,  and  again  after  cooling  down. 
In  1897  it  gave  me  great  pleasure  to  be  able  to  report  to  the  conven- 
tion of  the  American  Boiler  Manufacturers'  Association  that  in  more 
than  250  tests  of  steel  from  eight  different  mills  the  upper  limit  in 
sulphur  and  in  phosphorus  had  not  once  been  reached. 

Large  furnaces  for  heating  an  entire  flange  length  instead  of 
short  sections,  and  for  annealing  after  all  work  tending  to  distort  or 
set  up  shrinkage  strains  has  been  done,  insure  that  the  actual  structure 
will  carry  out  the  promise  of  the  test  piece. 

Rivets  and  stays  are  now  made  from  steel  of  the  same  high 
quality  as  boiler  plate.  There  was  much  prejudice  against  steel  rivets 
for  some  years,  and  high-grade  charcoal-iron  rivets  were  prescribed  by 
leading  authorities,  even  after  steel  plates  came  into  general  use. 
The  prejudice  was  finally  overcome  by  the  rational  work  of  the  rivet- 
makers  in  demonstrating  proper  methods  of  heating  and  driving, 
differing  much  from  those  in  vogue  with  iron  rivets. 

Tubes  also  have  undergone  progressive  evolution.  About  three 
years  ago  the  largest  tube  mill  in  the  country  publicly  announced 
that  it  would  no  longer  make  the  so-called  "charcoal"  iron  tubes. 
During  the  last  five  years  the  open-hearth  steel,  hot-rolled,  seam- 
less tubes  have  become  the  standard  for  high  grade  work.  Only 
architects  now  specify  charcoal-iron  tubes.  Their  reverence  for  the 
antique  is  touching  and  laudable,  but  should  not  be  extended  to 
metallurgy,  which  is  an  essentially  modern  science. 

Some  years  ago  I  made  exhaustive  tests  on  various  makes  of 
steel  and  iron  tubes.  The  iron  ran  about  48,000  pounds  per  square 
inch  tensile  strength  longitudinally,  but  only  36,000  transversely, 
and  the  steel  59,000  to  60,000  transversely  and  slightly  above  60,000 
longitudinally ;  so  that  a  steel  water-tube  is  about  66  per  cent  stronger 
than  an  iron  one.  Cold-drawn  steel  tubes  are  made  by  drawing 
hot-rolled  tubes  through  dies,  just  as  wire  is  drawn.  This  process 
gives  the  surfaces  a  polish  at  the  expense  of  ductility,  and  tubes  thus 
made  cannot  be  recommended  where  safety  and  durability  are  prime 
essentials. 

Cast  iron,  used  before  1890  very  generally  for  reinforcing  man- 
holes, for  feed  and  blow-off  pads  and  for  steam  saddles,  was  em- 
phatically condemned  in  the  American  Boiler  Manufacturers'  As- 
sociation specifications  of  1889,  and  forged  steel  of  best  quality 
is  now  used  for  such  parts.  Cast  iron  for  parts  under  tensile 
stress  was  prohibited,  and  in  1895  the  greatest  boiler  company  of 
the  country  marked  125  pounds  as  the  upper  limit  for  cast  iron 
headers. 

For  some  years  an  uncanny  metal  called  "flowed  steel,"  unknown 
to  metallurgical  experts,  was  recommended  to  a  credulous  and  un- 
discriminating  public,  but  it  has  faded  away  into  the  "Niffelheim" 
from  which  it  came. 


416  STEAM-BOILER  ECONOMY. 

Quality  of  Steel  in  a  Boiler  after  Thirty  Years  of  Service. — 

Three  horizontal  tubular  boilers  that  had  been  in  operation  30  years 
at  the  Lake  Superior  Iron  Mines,  Ishpeming,  Mich.,  were  condemned 
by  an  insurance  company  on  account  of  their  age,  although  they 
showed  no  sign  of  deterioration.  The  boilers  were  tested  to  destruc- 
tion by  hydraulic  pressure.  In  each  case  no  rupture  occurred  until 
a  pressure  of  275  Ibs.  per  sq.  in.,  or  upward,  was  reached,  and  in  each 
instance  the  manhole  frame  proved  to  he  the  weakest  part  of  the 
boiler.  Very  slight  leaks,  or  "weeping"  began  at  160  to  180  Ibs. 
Test  pieces  from  one  boiler  cut  from  the  shell  immediately  over 
the  fire  showed  an  average  tensile  strength  of  60,460  Ibs.,  elongation 
in  8  in.  .22.5%;  reduction  of  area  53.7%.  Analysis  gave  carbon, 
0.13;  sulphur,  0.026;  phosphorus,  0.097;  manganese,  0.27.  Test 
pieces  from  a  sheet  at  the  top  of  the  boiler  where  it  was  not  sub- 
jected to  the  action  of  the  fire  gave  an  average  tensile  strength  of 
70,145  Ibs.;  elongation  20.1%;  reduction  of  area  47.0%.  ;  elastic  limit 
39,060  Ibs.  The  steel  was  "Bay  State/'  made  about  1877.  It  was 
evident  that  there  had  been  no  deterioration  of  the  steel. —  (Power, 
Feb.  27,  1912). 

It  is  interesting  to  note  that  at  the  present  day  steel  that  gave 
the  results  above  stated  would  not  be  accepted  as  first  quality  boiler 
plate.  The  first  would  be  rejected  for  being  too  high  in  phosphorus, 
and  the  second  for  too  high  tensile  strength.  In  the  early  days  of 
the  manufacture  of  steel  for  boiler  plate  high  tensile  strength  and 
moderately  high  phosphorus  were  not  considered  as  objectionable  as 
they  now  are,  but  in  these  early  days  there  were  many  failures  of 
steel  plates  by  cracking  in  service,  which  were  generally  traced  to 
high  tensile  strength  and  brittleness  due  to  high  phosphorus. 

Boiler  Tubes. — Tubes  are  now  generally  made  of  soft  steel, 
but  charcoal  iron  tubes  are  preferred  by  some  authorities.  The 
American  Railway  Master  Mechanics  Association  in  its  revised  speci- 
fications of  1904  states  that  locomotive  tubes  shall  be  of  knobbled, 
hammered  charcoal  iron,  smooth  in  surface,  and  free  from  lamina- 
tions, cracks,  blisters,  pits  and  imperfect  welds.  Strips  planed  from 
the  tubes  heated  to  cherry  red  and  quenched  in  water  shall  be  bent 
and  hammered  down  flat  at  each  end  without  showing  crack  or  flaw, 
and  when  nicked  and  broken  shall  show  a  fracture  wholly  fibrous. 
A  section  of  tube  12  inches  long  shall  be  expanded  by  a  pin  tapered 
1J  in.  per  foot  till  the  end  is  expanded  to  1J  times  its  original 
diameter  without  splitting  or  cracking.  A  section  2£  in.  long  placed 
vertically  on  the  anvil  of  a  steam  hammer  and  subjected  by  light 
blows  must  crush  to  a  height  of  1|  in.  without  split  or  crack. 
Each  tube  must  be  tested  to  500  Ibs.  per  sq.  in.  hydraulic  pressure. 

Etching  Test. — In  case  of  doubt  as  to  the  quality  of  material, 


BOILER  DESIGN  AND  CONSTRUCTION. 


417 


the  following  test  shall  be  made  to  detect  the  presence  of  steel :  A 
section  of  tube,  turned  or  ground  to  a  perfectly  true  surface  on  the 
end,  will  be  polished  free  from  dirt  or  cracks,  and  the  end  of  the 
tube  will  be  suspended  in  a  bath  of  nine  parts  water,  three  parts 
sulphuric  acid  and  one  part  hydrochloric  acid.  The  bath  will  be 
prepared  by  placing  water  in  a  porcelain  dish,  adding  the  sulphuric 
and  then  the  hydrochloric  acid.  The  chemical  action  must  be  allowed 
to  continue  until  the  soft  parts  are  sufficiently  dissolved  so  that  the 
iron  tube  will  show  a  decided  ridged  surface,  with  the  weld  very 
distinct,  while  the  steel  tube  will  show  a  homogeneous  surface. 

Upsetting  Tubes. — For  marine  boilers  it  is  often  customary  to 
upset  or  thicken  the  tubes  at  the  ends  for  a  length  of  about  2-|  in. 
Greater  durability  is  claimed  for  such  upset  tubes.  The  Parkers- 
burg  Iron  Co.,  Parkersburg,  W.  Va.,  publishes  tables  giving  the 
amount  of  upsetting  or  increase  of  outside  diameter  allowed  for 
tubes  of  different  thicknesses,  from  which  the  following  figures  are 
taken : 


Thickness  of  tube,  B.W.G...  . 

10 

9 

8 

7 

6 

5 

4 

*in. 

Thickness  of  tube,  in  

o.r4 

0.148 

0.165 

0.182 

0.203 

0.219 

0.238 

0.250 

Ordinary  upset  in. 

13 

15 

17 

19 

20 

.22 

24 

25 

Advisable  limit,  in  

.10 

.20 

.25 

.28 

.30 

.33 

.36 

.38 

Possible,  but  difficult,  in  

.17 

.30 

.33 

.38 

.41 

.44 

.48 

.50 

Shells;  Water  and  Steam  Drums.  —  The  cylindrical  structure, 
including  the  ends,  of  a  fire-tube  boiler,  is  usually  called  the  shell. 
The  cylinder  superposed  on  the  tubes  of  a  water-tube  boiler  is  called 
a  water  and  steam  drum.  Shells  of  marine  boilers  of  the  Scotch 
type  have  been  built  of  diameters  as  large  as  16  ft.  Water  and  steam 
drums  of  water-tube  boilers  are  rarely  made  of  greater  diameter  than 
42  in. 

The  thickness  of  shell  for  a  given  pressure  is  found  from  the 
common  formula  for  safe  strength  of  thin  cylinders, 


MTf 
~ 


Whence     *-' 


PdF 


in  which  P  =  safe  working  pressure  ;  T  =  tensile  strength  of  plate,  both 
in  Ibs.  per  sq.  in.,  t=  thickness  of  plate  in  inches;  /=  ratio  of  the 
strength  of  a  riveted  joint  to  that  of  the  solid  plate;  F  =  factor  of 
safety  allowed;  and  d=  diameter  of  shell  or  drum  in  inches. 


418 


STEAM-BOILER  ECONOMY. 


The  value  taken  for  T  is  commonly  that  stamped  on  the  plates 
by  the  manufacturer,  /  is  taken  from  tables  of  strength  of  riveted 
joints  or  is  computed  as  shown  below,  and  F  must  be  taken  at  a 
figure  not  less  than  is  prescribed  by  local  or  State  laws,  or,  in  the  case 
of  marine  boilers,  by  the  rules  of  the  U.  S.  Board  of  Supervising 
Inspectors,  and  may  be  more  than  this  figure  if  a  greater  margin  of 
safety  is  desired. 

Strength  of  Circumferential  Seam,. — Safe  working  pressure  P  = 

A-f  7*/*  P V7  TP 

^  ;   t  =          ,  notation  as  above.      The  strength  of  a  shell  against 

rupture  on  a  circumferential  line  is  twice  that  against  rupture  on  a 
longitudinal  line,  therefore  single  riveting  is  sufficient  on  the  cir- 
cumferential seams  while  double,  triple  or  quadruple  riveting  is  used 
for  the  longitudinal  seams. 

Riveted  Joints. — Figs.  147  to  147d  show  the  usual  forms  of  riveted 
joints.  In  the  cuts  of  the  butt  and  double  strap  joints  the  dotted 


FIG.  147. — LAP  JOINT,  SINGLE-RIVETED. 


FIG.  147a. — LAP  JOINT,  DOUBLE- 
RIVETED. 


FIG.  1476. — BUTT  AND  DOUBLE  STRAP 
JOINT,  DOUBLE-RIVETED. 


FIG.  147c.-^-BuTT  AND  DOUBLE  STRAP 
JOINT,  TRIPLE-RIVETED. 


lines  indicate  the  width  of  the  bottom  strap  and  the  solid  lines  the 
width  of  the  narrower  upper  strap.  A  riveted  joint  may  fail  in 
either  one  of  several  ways:  1.  By  tearing  the  plate  along  a  line 


BOILER  DESIGN  AND  CONSTRUCTION. 


419 


through  a  row  of  rivets.  2.  By  shearing  the  rivets.  3.  By  crushing 
the  rivets  or  the  plate  in  front  of  the  rivets.  4.  If  the  lap  is  in- 
sufficient, by  splitting  or  shearing  the  edge  of  the  plate  in  front  of 
the  rivets.  5.  By  tearing  the  plate  and  shearing  some  of  the  rivets. 


FIG.  147d  —  BUTT  AND  DOUBLE  STRAP  JOINT,  QUADRUPLE-RIVETED.  ^ 

The  following  rules  for  proportioning  a  riveted  joint  so  as  to  obtain 
maximum  efficiency  are  given  by  F.  E.  Cardullo  : 

Let  t  =  the  thickness  of  the  main  plates. 

d  =  the  diameter  of  the  rivet-holes. 

/  =  the  tensile  strength  of  the  plate  in  pounds  per  sq.  in. 

s  =  the  shearing  strength  of  the  rivets  in  pounds  per  sq.  in. 
when  in  single  shear. 

p  =  the  distance  between  the  centers  of  rivets  of  the  outer  row 
(see  Figs.  147a  and  1476)  =  the  pitch  in  single  and  double 
lap  riveting  =  twice  the  pitch  of  the  inner  rows  in  triple 
butt  strap  riveting,  in  which  alternate  rivets  in  the  outer 
row  are  omitted  =  four  times  the  pitch  in  quadruple 
butt  strap  riveting,  in  which  the  outer  row  has  one- 
fourth  of  the  number  of  rivets  of  the  two  inner  rows. 
c  =  the  crushing  strength  of  the  rivets  or  plates  in  pounds  per 
sq.  in. 

n  =  the  number  of  rivets  in  each  group  in  single  shear.  (A 
group  is  the  number  of  rivets  on  one  side  of  a  joint  cor- 
responding to  the  distance  p-,  =  I  rivet  in  single  rivet- 
ing, 2  in  double  riveting,  5  in  triple  butt  strap  riveting, 
and  11  in  quadruple  butt  strap  riveting.) 

m  =  the  number  of  rivets  in  each  group  in  double  shear. 

s"  =  the  shearing  strength  of  rivets  in  double  shear,  in  pounds 
per  sq.  in.,  the  rivet  section  being  counted  once. 

T  =  the    strength    of    the    plate    at    the    weakest    section, 

=  ft(p-d). 
S  =  the  strength  of  the  rivets  against  shearing, 


C  =  the  strength  of  the  rivets  cr  the  plates  against  crushing, 
=  dtc(n  +  m). 


420  STEAM-BOILER  ECONOMY. 

In  order  that  the  joint  shall  have  the  greatest  strength  possible,  the 
tearing,  shearing,  and  crushing  strength  must  all  be  equal.  In  order 
to  make  it  so, 

1.  Substitute  the  known  numerical  values,  equate  the  expressions 
for  shearing  and  crushing  strength,  and  find  the  value  of  d,  taking  it 
to  the  nearest  ^  in. 

2.  Next  find  the  value  of  8  in  the  second  equation,  and  substitute 
it  for  T  in  the  first  equation.     Substitute  numerical  values  for  the 
other  factors  in  the  first  equation,  and  solve  for  p. 

The  efficiency  of  a  riveted  joint  in  tearing,  shearing  and  crushing, 
is  equal  to  the  tearing,  shearing  or  crushing  strength,  divided  by  the 
quantity  ftp,  or  the  strength  of  the  solid  plate. 

The  efficiency  in  tearing  is  also  equal  to  (p  —  d)  -r-  p. 

The  maximum  possible  efficiency  for  a  well-designed  joint  is 


E=m+n+( 

Empirical  formula  for  the  diameter  of  the  rivet-hole  when  the 
crushing  strength  is  unknown:  Assuming  thut  c  =  1.4/,  and  s"  = 
1.75*,  we  have  by  equating  C  and  8,  and  substituting, 


s(n  +  1.75m) 

Margin.  The  distance  from  the  center  of  any  rivet-hole  to  the 
edge  of  the  plate  should  be  not  less  than  Ijd  The  distance  between 
two  adjacent  rivet  centers  should  not  be  less  than  2d.  It  is  better 
to  increase  each  of  these  dimensions  by  %  in. 

The  distance  between  the  rows  of  rivets  should  be  such  that  the  net 
section  of  plate  material  along  any  broken  diagonal  through  the  rivet- 
holes  should  be  not  less  than  30  per  cent  greater  than  the  plate  section 
along  the  outer  line  of  rivets. 

The  thickness  of  the  inner  cover  strap  of  a  butt  joint  should  be 
%  of  the  thickness  of  the  main  plate  or  more.  The  thickness  of  the 
outer  straps  should  be  %  of  the  thickness  of  the  main  plate  or  more. 

Steam  Tightness.  It  is  of  great  importance  in  boiler  riveting 
that  the  joint  be  steam  tight.  It  is  therefore  necessary  that  the  pitch 
of  the  rivets  nearest  to  the  calked  edge  be  limited  to  a  certain  function 
of  the  thickness  of  the  plate.  The  Board  of  Trade  rule  for  steam 
tightness  is 

p=  Ct  +  If  in., 

where  p  =  the  maximum  allowable  pitch  in  inches ; 
t  =  the  thickness  of  main  plate  in  inches ; 
C  =  a  constant  from  the  following  table. 

No.  of  rivets  per  group ....  1  2  3  4  5 

Lapjoints C  =  1.31  2.62          3.47          4.14 

Double-strapped  joints . . . .   C  =  1 . 75  3 . 50          4 . 63          5 . 52         6 . 00 


BOILER  DESIGN  AND  CONSTRUCTION.  421 

The  pitch  should  not  exceed  ten  inches  under  any  circumstances. 

When  the  joint  has  been  designed  for  strength,  it  should  be 
checked  by  the  above  formula.  Should  the  pitch  for  strength  exceed 
the  pitch  for  steam  tightness,  take  the  latter,  substitute  it  in  the 
formula 

fl(p  -d)  =  0.7854rf2(w*  +  ms"), 

and  solve  for  d.     If  the  value  of  d  so  obtained  is  not  the  diameter  of 
some  standard  size  rivet,  take  the  next  larger  •£§  in. 

Efficiency  of  Riveted  Joints.     (Mass.  Boiler  Rules,  1910.)*' 

X  =  efficiency  =  ratio  of  strength  of  unit  length  of  riveted  joint  to  the  strength 

of  the  same  length  of  a  solid  plate. 

T  =  tensile  strength  of  the  material,  in  pounds  per  square  inch. 
t  =  thickness  of  plate,  in  inches. 
6  =  thickness  of  butt  strap,  in  inches. 

P  =  pitch  of  rivets,  in  inches,  on  the  row  having  the  greatest  pitch. 
d  =  diameter  of  rivet,  after  driving,  in  inches. 
a  =  cross-section  of  rivet  after  driving,  in  square  inches. 
[  s  =  strength  of  rivet  in  single  shear,  in  pounds  per  square  inch. 
S= strength  of  rivet  in  double  shear,  in  pounds  per  square  inch. 
c  =  crushing  strength  of  rivet,  in  pounds  per  square  inch. 
n  =  number  of  rivets  in  single  shear  in  a  length  of  joint  equal  to  P. 
N  =  number  of  rivets  in  double  shear  in  the  same  length  of  joint. 
For  single-riveted  lap  joints: 

A  =  strength  of  solid  plate  =  PtT. 

B  =  strength  of  plate  between  rivet  holes  =  (P—d)tT. 

C  =  shearing  strength  of  one  rivet  =  nsa. 

D  =  crushing  strength  of  plate  in  front  of  one  rivet =dtc. 

7?  C1  D 

X  =-r    or  -;     or    — ,  whichever  is  least. 
A          A  A 

For  double-riveted  lap  joints: 

A  and  B  as  above,  C  and  D  to  be  taken  for  two  rivets. 
X  =  B,  C,  or  D  (whichever  is  least)  divided  by  A. 
For  butt  and  double  strap  joint,  double-riveted: 
A  =  strength  of  solid  plate  =  PtT. 

B  =  strength  of  plate  between  rivet  holes  in  the  outer  row  =  (P  —  d)tT. 
C  =  shearing  strength  of  two  rivets  in  double  shear,  plus  shearing  strength 

of  one  rivet  in  single  shear  =  NSa-\-nsa. 

D  =  strength  of  plate  between  rivet  holes  in  the  second  row,  plus  the  shearing 

strength  of  one  rivet  in  single  shear  in  the  outer  row  =  (P— 2d)tT -\-nsa. 

E  =  strength  of  plate  between  rivet  holes  in  the  second  row,  plus  the  crushing 

strength  of  butt  strap  in  front  of  one  rivet  in  the  outer  row  =  (P—2d)tT 

+dbc. 

*  The  same  rules  are  given  in  the  A.  S.  M.  E.  Boiler  Code  of  1914,  which  was 
modeled  on  the  Massachusetts  Rules.  It  is  published  in  pamphlet  form  by  the 
American  Society  of  Mechanical  Engineers, 


422  STEAM-BOILER  ECONOMY. 

F  =  crushing  strength  of  plate  in  front  of  two  rivets,  plus  the  crushing  strength 

of  butt  strap  in  front  of  one  rivet  =  Ndtc+ndbc. 
G  =  crushing  strength  of  plate  in  front  of  two  rivets,  plus  the  shearing  strength 

of  one  rivet  in  single  shear  =  Ndtc -\-nsa. 
X  =B,  C,  D,  E,  F,  or  G  (whichever  is  least)  divided  by  A. 
For  butt  and  double  strap  joint,  triple-riveted: 

The  same  as  for  double-riveted,  except  that  four  rivets  instead  of  two  are 

taken  for  N  in  computing    C,  F,  and  G. 
For  butt  and  double  strap  joint,  quadruple-riveted: 
A,  B,  and  D  the  same  as  for  double-riveted  joints. 
C  =  shearing  strength  of  eight  rivets  in  double  shear  and  three  rivets  in  single 

shear  =  NSa+nsa. 

E= strength  of  plate  between  rivet  holes  in  the  third  row  (the  outer  row  being 
the  first)  plus  the  shearing  strength  in  single  shear  of  two  rivets  in  the 
second  row  and  one  rivet  in  the  outer  row  =  (P  —  4d)tT +nsa. 
F  =  strength  of  plate  between  rivet  holes  in  the  second  row,  plus  the  crushing 
strength  of  butt  strap  in  front  of  one  rivet  in  the  outer  row  =  (P  —  2d)tT 
+dbc. 

G  =  strength  of  plate  between  rivet  holes  in  the  third  row,  plus  the  crushing 
strength  of  butt  strap  in  front  of  two  rivets  in  the  second  row  and  one 
rivet  in  the  outer  row  =  (P— 4d)tT+ndbc. 
H  =  crushing  strength  of  plate  in  front  of  eight  rivets,  plus  the  crushing 

strength  of  butt  strap  in  front  of  three  rivets  =  Ndtc -\-ndbc. 
/  =  crushing  strength  of  plate  in  front  of  eight  rivets,  plus  the  shearing 
strength  in  single  shear  of  two  rivets  in  the  second  row  and  one  in  the 
outer  row  =  Ndtc +nsa. 

X=B,C,  D,  E,  F,  G,  H,  or  /  (whichever  is  least)  divided  by  A. 
The  Massachusetts  Rules  allow  the  crushing  strength  of  mild  steel  to  be 
taken  at  95,000  Ibs.  per  sq.  in.     The  maximum  shearing  strength  of  rivets, 
in  Ibs.  per  sq.  in.  of  cross-section,  is  taken  as  follows: 
In  single  shear,  iron,  38,000;   steel,  42,000. 
In  double  shear,  iron,  70,000;   steel,  78,000. 

The  A.  S.  M.  E.  Boiler  Code  also  allows  95,000  Ibs.  per  sq.  in.  for  crushing 
strength,  but  for  shearing  strength  of  rivets  allows: 
In  single  shear,  iron,  38,000  steel,  44,000. 
In  double  shear,  iron,  76,000;  steel,  88,000. 

Convex  or  Bumped  Heads. — When  the  head  is  of  material  of  the 
,came  quality  and  thickness  as  that  of  the  shell,  the  head  is  of  equal 

strength  with  the  shell  when  the  radius 
of  curvature  of  the  head  equals  the  diam- 
eter of  the  shell,  or  when  the  rise  of  the 
curve=0.134   diam.    of   shell.     Fig.    148. 
Thickness  of  Plates;  Riveting.  (Mass. 
Boiler    Rules,    1910.)— The    longitudinal 
FIG.  148.— BUMPED  HEAD,      joints  of  a  boiler,  the  shell  or  drum  of 
which  exceeds   36  in.  diameter,   shall  be  of  butt  and  double  strap 
construction;  if  it  does  not  exceed  36  in,  lap-riveted  construction 


BOILER  DESIGN  AND  CONSTRUCTION. 


423 


may  be  used,  the  maximum  pressure  on  such  shells  being  100  Ibs. 
per  sq.  in. 

The  longitudinal  joints  of  horizontal  return-tubular  boilers  shall 
be  located  above  the  fire-line  of  the  setting.  A  horizontal  return- 
tubular,  a  vertical  tubular,  or  a  locomotive  type  boiler  shall  not  have 
a  continuous  longitudinal  joint  over  12  ft.  in  length.* 

The  thickness  of  plates  in  a  shell  or  drum  shall  be  of  the  same 
gage.  The  minimum  thickness  of  plates  used  in  the  construction  of  a 
boiler  shall  be  i/4  in.  The  minimum  thickness  of  shell  plates  shall 
be  as  follows  : 


Diam.  36  in.  or  under,  14  in.  ;  over  36  to  54  in., 
to  72  in.,  %  in.  ;  over  72  in.,  i/2  in. 
Minimum  thickness  of  butt  straps: 


in.  ;  over  54 


Thickness  of  plates,  in.  .  . 
Min.  thickn.  of  straps,  in. 

ItoH 

¥ 

ftott 

AjoH 

*** 

ftof 

\ 

H«e«o|oo 

1  to  1ft 

Minimum  thickness  of  tube  sheets: 


Diam.  of  tube  sheet,  in  .... 
Thickness  of  tube  sheet,  in. 

42  or  under 
I 

over  42  to  54 
A 

over  54  to  72 
ft 

over  72 
A 

d  FP 
Minimum  thickness  of  convex  heads,  t  =  —  -^-;  d 


diameter  in 


inches;  F  =  5=  factor  of  safety;    P  =  working  pressure,  Ibs.  per  sq. 
in.  ;  T  =  tensile  strength  stamped  on  the  head. 


For  T=  50,000,  * 


dP 


40,'JOO 


;  forT7^  60,000,  t 


dP 

48,000 


When  a  convex  head  has  a  manhole  opening  the  thickness  is  to 
be  increased  not  less  than  %  in. 

[The  A.  S.  M.  E.  Boiler  Code  specifies  a  higher  factor  of  safety, 

5.5,  and  adds  y8  in.  to  the  thickness,  making  the  formula  -    ^-= — 

<i  1 

+  %  in.,  R  being  the  radius  to  which  the  head  is  dished,  in  inches. 
When  R  is  less  than  Q.8d  the  thickness  shall  be  at  least  that  found  by 
the  formula  when  R  =  O.Sd.  Dished  heads  with  the  pressure  on  the 
convex  side  are  allowed  a  maximum  working  pressure  equal  to  60% 
of  that  for  heads  of  the  same  dimensions  with  the  pressure  on  the 
concave  side.  When  the  dished  head  has  a  manhole  opening  the 
thickness  as  found  by  these  rules  shall  be  increased  by  not  less  than 
l/s  in-  The  corner  radius  of  a  dished  head  shall  be  not  less  than  IVo 
in.  nor  more  than  4  in.,  and  not  less  than  3%  of  R.  A  manhole  open- 


*  There  seems  to  be  no  good  reason  for  this  restriction. 
A.S.M.E.  Code. 


It  is  not  found  in  the 


424 


STEAM-BOILER  ECONOMY. 


ing  in  a  dished  head  shall  be  flanged  to  a  depth  not  less  than  three 
times  the  thickness  of  the  head  measured  from  the  outside.] 

Minimum  thickness  of  plates  in  flat-stayed  surfaces,  ^  in. 

The  ends  of  staybolts  shall  be  riveted  over  or  upset. 

Rivets  shall  be  of  sufficient  length  to  completely  fill  the  rivet 
holes  and  form  a  head  equal  in  strength  to  the  body  of  the  rivet. 

Rivets  shall  be  machine  driven  wherever  possible,  with  sufficient 
pressure  to  fill  the  rivet  holes,  and  shall  be  allowed  to  cool  and  shrink 
under  pressure. 

Rivet  holes  shall  be  drilled  full  size  with  plates,  butt  straps  and 
heads  bolted  in  position ;  or  they  may  be  punched  not  to  exceed  *4  in- 


ig  iii  FIG.  150. — SECTION 

— 6, I2"spaces=6'0—        — *  ;  OF  SEAM  ON  UN- 

DER    HALF     OF 
BOILER. 


FIG.  149. — QUADRUPLE-RIVETED  JOINT. 

less  than  full  size  for  plates  over  ^  in.  thick,  and  %  in.  or  less  for 
plates  not  exceeding  ^  in.  thick,  and  then  drilled  or  reamed 
to  full  size  with  plates,  butt  straps  and  heads  bolted  up  in  position. 

Quadruple  Riveted  Joint.— F.  W.  Dean,  (Power,  May  16,  1911) 
condemns  the  use  of  that  form  of  butt  and  strap  joint  in  which 
the  outside  strap  is  narrower  than  the  inside.  A  part  of  the  joint  is 
lapped  and  in  that  part  the  rivets  are  overhung  and  in  single  shear, 
and  the  whole  joint  may  be  deformed  under  strain.  Fig.  149  shows 
the  method  of  riveting  designed  by  Mr.  Dean  (after  German  marine 
practice)  for  a  horizontal  tubular  boiler  84  in.  diameter,  193  3  in. 
tubes  20  ft.  long,  3056  sq.  ft.  of  heating  surface.  Both  butt  straps 
are  the  same  size,  %  in.  thick.  The  rivets  are  %  in-  diam.,  4  in. 
pitch.  An  efficiency  of  92  per  cent  may  be  obtained  with  this  form 
of  joint.  The  plates  at  the  circumferential  seams  are  thinned  down 
on  the  under  half  of  the  boiler,  as  shown  in  Fig.  150  to  avoid  having 
too  great  a  double  thickness  of  seam. 

Working  Pressure  on  Boilers  with  Triple  Riveted  Joints. — A 
triple  riveted  double  butt  and  strap  joint,  carefully  designed,  may  be 
made  to  have  an  efficiency  something  higher  than  85  per  cent.  Good 
boiler  plate  steel  may  be  considered  to  have  a  tensile  strength  of 
55,000  Ibs.  per  sq.  in.  Taking  these  figures  and  a  factor  of  safety 
of  5,  we  have  safe  working  pressure 

2Ttf  _  2  X  55,000  X  t  X  0.85  _  18700^ 

•*•         7    1-1         ^      T  1  5 


from  which  the  following  table  is  calculated. 


BOILER  DESIGN  AND  CONSTRUCTION. 


425 


SAFE   WORKING   PRESSURE   FOR  SHELLS  WITH   JOINTS   OF  85%   EFFICIENCY. 


Thickness,  inches  

H 

& 

H 

A 

Y* 

A 

5/8 

H 

H 

tt 

X 

H 

1 

Diameter,  inches  24 

195 
156 
130 
111 

247 
195 
162 
139 
122 
108 

234 
195 
167 
146 
130 
117 
106 

227 
195 
170 
151 
136 
124 
114 

260 
223 
195 
173 
156 
142 
130 
120 

250 
219 
195 
175 
159 
146 
135 
125 
117 

243 
216 
195 
177 
162 
150 
139 
130 
121 

238 
214 
195 
179 
165 
153 
143 
134 

233 
212 
195 
180 
167 
156 
146 

230 
211 
195 
181 
169 
158 

227 
210 
195 
182 
170 

225 
209 
195 
183 

223 
208 
195 

30 
36 
42 

48 
54 
60 
66 
72 
78 
84 
90 
96 

... 

Shells  of  externally-fired  boilers  are  rarely  made  over  ^  in.  thick. 

Pressures  Allowed  on  Boilers.  (Mass.  Boiler  Rules,  1910.) — The 
pressure  allowed  on  a  boiler  constructed  wholly  of  cast  iron  shall 
not  exceed  25  Ibs.  per  sq.  in. 

The  pressure  allowed  on  a  boiler  the  tubes  of  which  are  secured 
to  cast-iron  headers  shall  not  exceed  160  Ibs.  per  sq.  in. 

The  maximum  pressure  to  be  allowed  on  a  shell  or  drum  of  a 
boiler  shall  be  determined  from  the  minimum  thickness  of  the  shell 
plates,  the  lowest  tensile  strength  stamped  on  the  plates  by  the  man- 
ufacturer, the  efficiency  of  the  longitudinal  joint  or  of  the  ligament 
between  the  tube  holes,  whichever  is  least,  the  inside  diameter  of  the 
outside  course,  and  a  factor  of  safety  not  less  than  five. 

The  lowest  factor  of  safety  to  be  used  for  boilers  the  shells  or 
drums  of  which  are  exposed  to  the  products  of  combustion,  and  the 
longitudinal  joints  of  which  are  lap  riveted,  shall  be  as  follows : 
5  for  boilers  not  over  10  years  old ;  5.5  for  boilers  over  10  and  not 
over  15  years  old;  5.75  for  boilers  over  15  and  not  over  20  years 
old;  6  for  boilers  over  20  years  old.  The  lowest  factor  of  safety  to 
be  used  for  boilers  the  longitudinal  joints  of  which  are  of  butt 
and  double  strap  construction  is  4.5. 

A  hydrostatic  test  is  to  be  applied  if  in  the  judgment  of  the 
inspector  or  of  the  insurance  company  it  is  advisable.  The  maximum 
pressure  in  a  hydrostatic  test  shall  not  exceed  1J  times  the  maximum 
allowable  working  pressure,  except  that  twice  the  maximum  allowable 
working  pressure  may  be  applied  on  boilers  permitted  to  carry  not 
over  25  Ibs.  pressure,  or  on  pipe  boilers. 

All  steam  boilers  and  their  appurtenances  except  [here  follows 
a  list  of  exceptions,  covering  locomotives,  agricultural  boilers,  heat- 
ing boilers,  boilers  of  not  more  than  3  H.P.,  and  boilers  under  the 
jurisdiction  of  the  United  States]  shall  be  thoroughly  inspected 
internally  and  externally  at  intervals  of  not  over  one  year,  and  shall 


426 


STEAM-BOILER  ECONOMY. 


not  be  operated  at  pressures  in  excess  of  the  safe  working  pressure 
stated  in  the  certificate  of  inspection. 

Making  a  Boiler  Shell. — The  several  sheets  of  which  the  shell 

is  to  be  constructed  are  sheared  to  the  exact  size  called  for  in  the 

drawings,  the  rivet  holes  are  located  by  means  of  wooden  templates 

and  their  centers  prick  punched,  or  else  the  holes  are  spaced  and 
punched  by  automatic  machinery.  The  holes 
for  all  nozzles  and  screwed  pipe  connections 
are  located  and  punched  or  cut.  The  operation 
of  punching  a  rivet  hole  is  shown  in  Fig.  151. 
The  metal  in  the  immediate  vicinity  of  the 
hole  is  strained  and  hardened  by  the  action  of 

FIG.  151.— PUNCHING  A  the  punch,  and  therefore  it  is  required  in  the 
best  boiler-making  practice  that  the  holes  be 

punched  smaller  than  their  full  size  and  finished  to  size  by  drilling 

or  reaming  after  the  plates  have  been  rolled  and  bolted  in  position. 
After  cutting  the  holes  the   edges  of  the  plates   are  planed   or 

cut  with  chisels  to  make  smooth  the  edges  that  are  left  rough   in 

shearing,  and  where  lap  joints  are 

to  be  made  the  plates   are  beveled 

to   a   thin   edge    so   that   the   joint 

may  be  made  tight  by  calking.    Fig. 

152  shows  how  plates  are  "scarfed" 

and    joined    together    at   the   meet- 
ing  point   of   a    horizontal    and    a 

girth  lap  joint. 

After     punching,     drilling    and 

planing,    the    plate    is    rolled    into 

the  required  shape,,  by  being  passed 

back  and  forth  between  three  rolls, 

the    top    one  'of    which    is    forced 

downward  by  screws  as  the  radius 

of  the  bend  becomes  smaller.     The 

bending   is   done   slowly   so   as   not 

to  overstrain  the  metal,  the  amount  of  curvature  made  at  each  pass 

being  less  for  a  thick  plate  than  for  a  thin  one. 

After   rolling  to  shape,   the  rivet  holes   of  a  joint   are   brought 

together  by  means  of  drift  pins  and  bolts  and  such   irregularities 

as  are  found  to  exist,  on  account  of  the  change  in  dimensions  with 

rolling,  are  reamed  out  by  passing  a  reamer  or  drill,  the  full  size  of 


;    o 

0    |    0        0 

0        0 

0 

r 

XX       XX      XV 


FL ' " '     > 


FIG.  152. — PLATES  SCARFED  AT 
MEETING  OF  JOINTS. 


BOILER  DESIGN  AND  CONSTRUCTION. 


427 


the  rivet  hole,  through  each  pair  of  holes  which  come  together. 
After  a  few  rivet  holes  have  been  drilled,  stay  rivets  are  put  in  and 
headed  over  and  the  drift  pins  or  bolts  may  be  taken  out  as  the  stay 
rivets  hold  the  joints  in  position,  and  the  riveting  of  the  joint  is 
then  completed.  Hydraulic  or  other  machine  riveting  is  used  wherever 
possible,  as  it  generally  makes  a  tighter  joint  than  hand  riveting. 

Flanged  heads  are  usually  formed  to  shape  in  hydraulic  presses, 
the  metal  being  heated  to  redness.    It  is  important  to  heat  the  plate 

evenly  throughout  and  to  complete 
the  flanging  while  the  metal  is 
still  at  a  red  heat.  Flanging 
at  a  '"blue"  heat,  that  is,  below 


FIG.  153. — TAPER-PIN  TUBE  EXPANDER.  FIG.  154. — ROLLER  EXPANDER. 

redness,  is  apt  to  cause  cracking.  After  flanging  the  head  should 
be  annealed  by  heating  to  dull  red  in  an  annealing  furnace  and  cool- 
ing slowly. 

Holes  for  tubes  are  cut  in  the  tube  sheets  by  a  spiral  punch  or 
a  revolving  cutter.  The  tubes  are  secured  to  the  tube  sheets  by  means 
of  expanding  tools,  such  as  are 
shown  in  Figs.  153  and  154.  Care 
must  be  taken  to  continue  the  ex- 
panding process  until  a  thoroughly 
tight  joint  is  made,  pressing  the 
tube  against  the  tube  sheet  suf- 
ficiently to  cause  a  slight  groove  in 
the  tube,  but  not  so  far  as  to  need- 
lessly thin  down  the  tube.  When 
the  expanding  is  properly  done  the 
tube  sheets  are  strongly  stayed  by 


the  tubes  so  that  no  flaring  or  bead-  FIG.    155.  —  TUBE       FIG.  156.— Ex- 
P  , ,  i      <•  ,1      .    i  EXPANDED  INTO  PANDED  AND 

ing  over  of  the  end  of  the  tube  is       SHEET.  FLARED. 

necessary,  but  it  is  customary  in 

fire-tube  boilers  to  form  a  bead  on  the  end  of  the  tube  and  make  a 
good  finish.  Figs.  155  and  156  show  two  examples  of  expanded  tubes, 
the  first  in  which  the  tube  is  merely  expanded ;  the  second  one  shows 
the  tube  flared  at  the  end  after  expanding. 


428 


STEAM-BOILER  ECONOMY. 


Mass.  Boiler  Rules. — Tube  holes  shall  be  drilled  full  size,  or  they 
may  be  punched  not  to  exceed  J  in.  less  than  the  full  size,  and  then 
drilled,  reamed  or  finished  full  size  with  a  rotating  cutter.  The 
edge  of  tube  holes  shall  be  chamfered  to  a  radius  of  about  ^  in. 
A  fire-tube  boiler  shall  have  the  ends  of  the  tubes  substantially 
beaded.  The  ends  of  all  tubes,  suspension  tubes  and  nipples  shall 
be  flared  not  less  than  J  in.  over  the  diameter  of  the  tube  hole  on 
all  water- tube  boilers  and  superheaters,  and  shall  project  through 
the  tube  sheets  or  headers  not  less  than  J  in.  nor  more  than  \  in. 
Separately  fired  superheaters  shall  have  the  tube  ends  protected  by 
refractory  material  where  they  connect  with  drums  or  headers. 

Holding  Power  of  Expanded  Tubes.  (The  Locomotive,  Sept. 
1893.) — Tubes  3  in.  external  diameter,  0.109  in.  thick  were  expanded 
in  a  f-in.  plate  by  rolling  with  a  Dudgeon  expander,  without  the 
projecting  part  being  flared  or  beaded.  Stress  was  applied  to  draw 
the  tubes  out  of  the  plates.  The  observed  stress  which  caused 
yielding  was,  in  three  specimens,  6500,  5000  and  7500  Ibs.  Two 
other  specimens  were  flared  so  that  the  diameter  of  the  extreme  end 
of  the  tube,  projecting  -£$  in.  beyond  the  plate  was  3. 2  in.,  the  diameter 
of  the  tube  where  it  entered  the  plate  being  3.1  in.  The  observed 
stress  which  caused  the  yielding  of  these  specimens  was  21,000  and 
19,500  Ibs.  The  Locomotive  estimates  that  the  factor  of  safety  of 
the  plain  rolled  tubes  is  nearly  4  and  that  of  the  flared  tubes  about 
15  against  the  stress  to  which  they  are  subjected  in  a  boiler  at  100 
Ibs.  gage  pressure.  It  is  considered  that  the  tubes  act  as  stays  for 
that  portion  of  the  flat  head  that  is  within  two  inches  of  the  upper  row 
of  tubes,  and  that  the  segment  above  this  (except  that  portion  that 
lies  with  3  ins.  of  the  shell)  requires  to  be  braced. 

The  stress  that  acts  on  each  tube  tending  to  pull  it  out  of  the 
head  may  be  calculated  as  follows :  Multiply  the  area  of  that  por- 
tion of  the  head  that  is  stayed  by  the 
tubes,  in  square  inches,  minus  the  sum 
of  the  areas  corresponding  to  the  ex- 
ternal diameter  of  the  tubes,  by  the 
maximum  pressure  of  steam  the  boiler 
is  allowed  to  carry  in  Ibs.  per  sq.  in., 
and  divide  the  product  by  the  number 
of  tubes. 

Calking. — Fig.  157  shows  the  opera- 
tion of  calking  the  edge  of  a  lap  seam 
FIG.  157.— CALKING  OP  JOINTS     an(j  aiso  calking  the  head  of  a  rivet. 

AND    RlVETS.  ..  1,11          n  -,     i  T      . 

A  round-nosed  tool  should  be  used  in 

order  to  avoid  cutting  the  plate.     The  tool  is  struck  with  a  hammer 
with  sufficient  force  to  drive  the  edge  of  the  plate  or  of  the  rivet 


BOILER  DESIGN  AND  CONSTRUCTION. 


429 


head  down  to  a  firm  bearing  so  as  to  close  the  joint  completely  and 
prevent  leaks.     Too  heavy  a  blow  is  apt  to  open  the  joint. 

Braces  and  Stays. — The  flat  surfaces  of  a  boiler  which  are  not 
stayed  by  the  tubes  require  to  be  stayed  by  other  means.  "Through" 


FIG.  158. — END  OF  A 
THROUGH  STAY. 


FIG.  159. — CHANNEL  REINFORCEMENT  FOR 
STAYS. 


stays,  which  run  direct  from  one  head  to  the  other  are  commonly 
used  in  marine  boilers  of  the  Scotch  type,  see  Fig.  100,  page  350,  and 
to  some  extent  in  large  high-pressure  return  boilers.  Fig.  158  shows 


FIG.  160. — DIAGONAL  AND  THROUGH 
BRACING. 


FIG.  161. — CROW-FOOT  BRACES. 


FIG.  162. — BRACE  MADE  OP 
BENT  PLATE. 


one  method  of  securing  the  end  of  a  through  stay  rod  to  the  head. 
Fig.  159  shows  channel  bars  riveted  to  the  inside  of  a  boiler  head 
to  reinforce  the  sheet  at  the  through  stay  connections. 

Fig.  160  shows  one  form  of  diagonal  stay  and  also  a  through  stay. 

Fig.  161  shows  an  old  form  of  "crow-foot"  brace,  used  for  bracing 
tubular  boilers,  and  Fig.  163  .shows  the  position  of  the  feet  of  these 


430 


STEAM-BOILER  ECONOMY. 


braces  in  the  head,  the  little  circles  representing  the  position  of 
the  rivet  holes.  The  dotted  lines  enclose  the  area  that  requires 
bracing. 

Fig.  162  shows  a  common  form  of  crow-foot  brace  made  out  of  steel 
plate  bent  to  shape.    It  is  known  as  the  McGregor  brace. 


<* 


ooooooo 
ooooooo 
ooooooo 
ooooooo 
oooooo 
ooooo 
oooo 


ooooooo 

ooooooo 

ooooooo 

ooooooo 

oooooo 

ooooo 

oooo 


o 

~" 

FIG.  163. — ARRANGEMENT  OF  STAYS  AND  TUBES. 


FIG.  164. — BRACES 
WITH  T-BARS. 


Fig.  164  shows  the  braces  used  with  the  T-irons  shown  in  Fig.  165. 
The  T-bars  are  riveted  to  the  head  for  attachment  of  the  stays.  Fig. 
166  shows  methods  of  fastening  stays  to  the  heads  and  to  the  shell. 


FIG.  165. — T-BAR  ATTACHMENT  FOR  STAYS. 

Fig.  167  shows  three  methods  of  bracing  the  flat  top  or  "crown 
sheet"  of  a  fire  box  or  combustion  chamber,  such  as  that  of  a  locomotive., 
or  of  an  internally  fired  marine  boiler.  At  the  left  a  pair  of  "crown 
bars"  is  shown  in  section.  The  bars  extend  the  width  of  the  fire 
box  and  are  bent  down  and  forged  into  feet  at  the  end  so  as  to  rest 
on  the  edges  of  the  side  plates.  The  downward  pressure  of  steam, 
which  tends  to  crush  in  the  flat  top,  is  conveyed  by  bolts  and  nuts 


BOILER  DESIGN  AND  CONSTRUCTION. 


431 


to  caps  which  straddle  a  pair  of  bars.  In  the  two  other  methods, 
shown  at  the  right,  the  load  is  transmitted  by  stays  to  the  upper 
shell  of  the  boiler. 


FIG.  166. — METHODS  OF  FASTENING  BRACES. 


FIG.  167. — METHODS  OF  BRACING  A  CROWN  SHEET. 

Allowable  Stresses  on  Braces  and  Staybolts.  (Massachusetts 
Eules.) — The  maximum  allowable  stress  per  square  inch  net  cross- 
sectional  area  of  stays  and  stay  bolts  shall  be  as  follows :  Weldless 
mild  steel,  head  to  head  or  through  stays,  8000  Ibs.,  9000  Ibs. ; 
diagonal  or  crow-foot  stays,  7500  Ibs.,  8000  Ibs. ;  mild  steel  or  wrought- 
iron  staybolts  6500  Ibs.,  7000  Ibs.  The  first  figure  in  each  case  is 
for  size  up  to  1J  in.  diameter  or  -equivalent  area,  the  second  for 
size  over  1J  in.  or  equivalent  area. 

The  A.  S.  M.  E.  Boiler  Code  allows  for  welded  stays  6000  Ibs.  per 
sq,  in.;  for  unwelded  stays,  (a)  7500;  (b)  9500;  (c)  8500.  (a)  less 
than  20  diameters  long,  screwed  through  plates  with  ends  riveted  over ; 
(b)  lengths  between  supports  not  exceeding  120  diameters:  (c)  ex- 
ceeding 120  diameters. 

Stay-bolts. — Stay-bolts  in  water-legs  are  subject  not  only  to 
longitudinal  stress  due  to  the  boiler  pressure,  and  to  corrosion,  but 
also  to  bending  stress  caused  by  relative  motions  of  the  outer  and 
inner  sheets  of  the  furnace  or  water-leg  due  to  the  variations  in 
temperature  to  which  the  two  are  subjected.  A  stay-bolt  usually 


432  STEAM-BOILER  ECONOMY. 

fails  by  transverse  fracture  close  to  the  outer  sheet,  which  is 
supposed  to  be  due  to  the  fact  that  the  fire-box  sheet  is  generally 
thinner  than  the  outer  sheet,  and  therefore  holds  the  end  of 
the  stay  less  rigidly.  Fig.  168  shows  a  stay-bolt  drilled  with 
a  small  hole  at  one  end  through  which  water  will  be  blown 
out  as  soon  as  a  fracture  extends  far  enough  across  the  section 
to  reach  the  hole,  thus  calling  attention  to  the  failure  of  the  stay. 
Fig.  169  shows  a  better  form,  in  which  the  hole  extends  the  whole 
length  of  the  stay.  The  inner  portion  of  the  stay  is  turned  to  %  in- 


FIG.  168. — STAY  BOLT,  DRILLED  AT  FiG.~169. — HOLLOW  STAY  BOLT. 

ONE  END. 

smaller  diameter   than  the  ends,   in   order  to   make  the  stay   more 
flexible  and  diminish  the  chances  of  fracture. 

"Flexible  Spring  Stay-bolt .— H.  V.  Wille,  (Trans.  A.  S.  M.  E., 
1909)  describes  a  flexible  stay-bolt  made  of  oil-tempered  spring  steel 
that  will  safely  stand  a  tensile  stress  of  100,000  Ibs.  per  sq.  in.  Its 

high  elastic  limit  makes  it  possible  to 
reduce  the  diameter  to  %  in.  or  less. 
The  bolts  are  slightly  enlarged  and 
threaded  at  the  ends  and  screwed  into 
soft  steel  end  pieces  which  are  screwed 
FIG.  170.— FLEXIBLE  STAY-BOLT,  into  the  plates  and  headed  up  in  the 

usual  manner  (Fig.  170). 

Stay-bolts  fail  not  because  of  the  tensional  loads  upon  them, 
but  from  flexural  stresses  induced  by  the  vibration  resulting  from 
the  greater  expansion  of  the  fire-box  sheets  than  of  the  outside  sheets. 
It  is  general  practice  to  recess  the  bolts  below  the  base  of  the  threads 
and  this  has  effected  a  slight  reduction  in  the  fiber  stress,  but 
practically  no  effort  has  been  made  to  design  a  bolt  to  meet  the 
flexural  stresses  or  even  to  calculate  their  magnitude.  The  stress 
increases  in  direct  proportion  to  the  diameter  and  decreases  as  the 
square  of  the  distance  between  the  sheets. 

Flat  Surfaces  Supported  by  Stay-bolts.  A.  J.  Toppm  (Power, 
Dec.  24,  1912). — There  seems  to  be  a  difference  of  opinion  relative 
to  the  allowable  pressure  for  a  given  thickness  of  plate  and  pitch  of 
rivets  Formulas  by  different  authorities  give  notably  different  results. 
Massachusetts,  Ohio  and  the  city  of  Detroit  employ  the  formula : 

66(?-f  I)2 


BOILER  DESIGN  AND  CONSTRUCTION.  433 

in  which  P  =  safe  working  pressure  in  pounds  per  square  inch  ;  I  =  ' 
thickness  of  plate  in  sixteenths  of  an  inch;  66  =  a  constant  determined 
by  experiment;  S  =  maximum  pitch  in  inches. 
The  United  States  Government  rule  is  : 


in  which  P,  £,  and./S'  are  the  same  symbols  as  in  the  previous  formula, 
and  k  is  a  constant  depending  on  the  method  of  staying.  For  screwed 
stays  riveted  over  and  plates  not  exceeding  ^  in.  thick,  k=  112.  For 
the  same  conditions  and  plates  over  ^&  in-  thick,  k  =  120. 

'To  determine  the  area  of  bolt  necessary  to  sustain  the  load,  let 
P=  pressure  in  Ibs.  per  sq.  in.;  Smex,  =  maximum  pitch  in  inches; 
$min.  =  minimum  pitch  in  inches;  A  =  net  area  under  pressure  in 
square  inches;  D  =  outside  diameter  of  stay-bolt  in  inches;  T  =  the 
allowable  tensile  strength  of  the  stay-bolt  in  Ibs.  per  sq.  in.;  d  =  diam- 
eter at  root  of  thread  of  stay-bolt. 

The  net  area  supported  by  one  stay-bolt  would  be  the  product  of  the 
two  pitches  minus  the  area  of  stay-bolt  at  the  root  of  the  thread,  or 

.  X  ^min.)  T~  • 

The  load  sustained  by  the  stay-bolt  would  be  P  times  this  area.     The 

ird2 
strength  of  the  stay-bolt  would  be  T  X  -y-.    As  this  must  balance  the 

load 


Transposing, 


-i  Q-*  \J-  '-'max.  X 


Stay-bolts  1J  in.  in  diameter  and  under,  generally  have  12  threads 
per  inch  and  the  outside  diameter 

D=d  +  0.1443. 
Substituting  in  the  foregoing,  we  obtain 


T)        £)-*-     ^max.  X  £>min.     ,     r\   1AAQ 

=  ir(T+P) *"  ' 

The  value  of  T  varies  according  to  different  authorities.  Massa- 
chusetts allows  only  6500  Ibs.  per  square  inch  on  mild  steel  or 
wrought-iron  stay-bolts  up  to  and  including  1J  in.  diameter.  The 
United  States  Government  allows  8000  for  tested  steel  stays  1J  to 
2J  in.  diameter  when  not  forged  or  welded. 


434 


STEAM-BOILER  ECONOMY. 


For  hollow  stays  the  reduction  in  area  due  to  the  diameter  of 
the  hole  must  be  taken  into  account  in  computing  the  strength  of  the 
stay. 

From  these  formulae  Mr.  Toppin  calculates  a  series  of  tables 
for  the  allowable  pressures  corresponding  to  different  diameters  and 
pitches  of  stays  and  thicknesses  of  plates  and  plots  the  curves  shown 
in  Figs.  171  and 


12  JL6    20    24    28    32    36    40    44    48    52    56    60   64 
Area  to  be  supported  in  Square  Inches 


4  4ya  5  sl/&  6  ey3  i  iy%  8 

Pitch  of  Stay-bolts  in  Ins. 


FIG.  171. — ALLOWABLE  PRESSURES  ON  STAY-    FIG.   172. — ALLOWABLE   PRES- 
BOLTS  AT  6500  LBS.  STRESS.  SURES  ON  PLATES  OF  VARIOUS 

THICKNESS  AND  PITCHES. 

For  calculating  allowable  pressure:  at  7000  Ibs.  per  square  inch  stress,  multiply  the 
pressure  given  in  tables  by  1.077.  At  7500  Ibs.  multiply  by  1.157.  At  8000  Ibs.  multiply 
by  1.232.  At  6000  Ibs.  multiply  by  0.922. 


ALLOWABLE    PRESSURES    ON    STAY-BOLTED    FLAT    SURFACES    ACCORDING    TO 
MASSACHUSETTS    FORMULA. 


Thickness  of  Plate  in 
Inches. 

Allowable  Pressures  on  Stay-bolted  Flat  Plate.      Varying  Pitch  and  Thickness. 

Maximum  Pitch  in  Inches. 

4 

4* 

4* 

4| 

4* 

4| 

41 

5 

5i 

5* 

52 

6 

61 

6* 

6} 

7 

71 

7J 

71 

8 

I 

\ 

165 
237 

149 
215 

136 
197 

125 
180 

115 
166 
227 

107 
154 
210 

99 
143 
195 

86 
125 
170 
222 

76 
110 
150 
195 

68 
98 
133 
174 
220 

61 
87 
119 
156 
197 

55 
79 
107 
140 
178 
220 

49 
71 
97 
127 
161 
199 

45 
65 
89 
116 
147 
182 
220 

41 
60 
81 
106 
135 
166 
201 

38 
55 
75 
98 
124 
153 
185 

35 
51 
69 
90 
114 
141 
171 

32 
47 
64 
84 
106 
131 
158 

30 
43 
59 
78 
98 
122 
147 

28 
40 
55 
72 
92 
113 
137 

BOILER  DESIGN  AND  CONSTRUCTION.  435 

The  above  table  was  calculated  according  to  Massachusetts  formula 

p_66«+l)2 
"     52-6     ' 

in    which    P=  allowable    pressure  in  pounds  per  square  inch;    S=  maximum  pitch  in  inches: 
t  =thickness  of  plates  in  sixteenths  of  an  inch;  66  =  a  constant  determined  by  experiment 

ALLOWABLE    PRESSURES    ON    STAY-BOLTED    FLAT    SURFACES    ACCORDING   TO 
U.    S.    GOVERNMENT   FORMULA. 


Thickness  of  Plate  in  Inches. 

Allowable  Pressures  on  Stay-bolted  Flat  Plates.              Varying  Pitch  and  Thickness. 

Maximum  Pitch  in  Inches. 

4 

105 
164 

4K 

4% 

434 

4^8 

4M 

5 

5M 

5H 

55* 

6 

6M 

6K2 

Vi 

7 

7* 

7H 

29 
46 
67 
89 
128 
161 
199 

8 

28 
43 
64 
83 
'120 
151 
187 

1 
i 

112 
175 

99 
155 
223 

93 
146 
210 

88 
138 
199 

83 
134 

188 

79 
124 

178 

71 
112 
161 
215 

65 
101 
149 
195 

59 
92 
133 
178 

54 
84 
122 
163 

49 
77 
112 
149 
213 

45 
71 
103 
138 
196 

42 
66 
96 
127 
181 

39 
61 
88 
118 
168 
213 

36 
57 
82 
109 
156 
198 

34 
53 
76 
102 
146 
184 

31 
49 
71 
95 
136 
172 
213 

The  above  table  calculated  according  to  the  U.  S.  Government  formula, 


in  which  A;  =a  constant;   S  =max.  pitch;  t  =thickness  of  plate  in  sixteenths  of  an  inch;   k  =112 
for  plates  up   to  7/16  in.;  k  =  120  for  plates  over  7/l6  in. 

The  A.  S.  M.  E.  Boiler  Code  gives  the  same  formula  as  the  U.  S. 
Government  with  the  following  values  of  the  constants :  For  stays 
screwed  through  plates  with  ends  riveted  over,,  plates  not  over  -^ 
in.  thick,  C  =  112;  over  T^  in.  thick,  C  =  120;  for  stays  screwed 
through  plates  and  fitted  with  single  nuts  outside  of  plate,  C  =  135 ; 
for  stays  fitted  with  inside  nuts  and  outside  washers,  the  diameters 
of  washers  not  less  than  0.4$  and  thickness  not  less  than  t,  C  =  175. 

Size  of  Boiler  Tubes. — The  following  table  gives  the  dimensions 
of  the  tubes  commonly  used  in  steam  boilers,  together  with  their  cal- 
culated surface  per  foot  of  length,  and  the  length  per  square  foot 
of  surface,  internal  and  external: 


External 
Diam- 
eter. 
In. 

Standard 
Thick- 
ness. 
In. 

Inside 
Diam- 
eter. 
In. 

Inside 
Surface 
per  Foot 
of  Length. 

Length 
per  Sq.ft. 
of  Inside 
Surface. 

Outside 
Surface 
per  Foot 
of  Length, 

Length 
per  Sq.ft. 
Outside 
Surface, 

Internal 
Area, 
Sq.ft. 

External 
Area, 
Sq.ft. 

Sq.ft. 

Ft. 

2       • 

.095 

1.810 

0.4738 

2.110 

0.5236 

.910 

0.0179 

0.0218 

2J* 

.095 

2.060 

.5393 

1.854 

.5890 

.698 

.0231 

.0276 

2H 

.109 

2.282 

.5974 

1.674 

.6545 

.528 

.0284 

.0341 

2^ 

.109 

2.532 

.6629 

.508 

.7199 

.389 

.0350 

.0412 

3 

.109 

2.782 

.7283 

.373 

.7854 

.273 

.0422 

.0491 

3K 

.120 

3.010 

.7880 

.269 

.8508 

.175 

.0494 

.0576 

3^i 

.120 

3.260 

.8535 

.172 

.9163 

.091 

.0580 

.0668 

3^* 

.120 

3.510 

.9189 

1.088 

.9817 

1.018 

.0672 

.0767 

4 

.134 

3.732 

.9770 

1.024 

1.0472 

0.955 

.0760 

.0873 

1 

436 


STEAM-BOILER  ECONOMY. 


Pines  Subjected  to  External  Pressure. — The  General  Rules  and 
Regulations  of  the  IT.  S.  Board  of  Supervising  Inspectors,  Steam- 
boat Inspection  Service,,  1909,  give  the  following  rules  for  flues 
subjected  to  external  pressure  only : 

Plain  lap-welded  flues  7  to  13  in.  diameter. 

Furnaces. — The  tensile  strength  of  steel  used  in  the  construction 
of  corrugated  or  ribbed  furnaces  shall  not  exceed  67,000,  and  be 
not  less  than  543000  Ibs. ;  and  in  all  other  furnaces  the  minimum 
tensile  strength  shall  not  be  less  than  58,000,  and  the  maximum  not 
more  than  67,000  Ibs.  The  minimum  elongation  in  8  inches  shall  be 
20%. 

All  corrugated  furnaces  having  plain  parts  at  the  ends  not 
exceeding  9  inches  in  length  (except  flues  especially  provided  for), 


FIG.  173. — TUBE-SPACING  IN  A  HORIZONTAL  BOILER. 

when  new,  and  made  to  practically  true  circles,  shall  be  allowed  a 
steam  pressure  in  accordance  with  the  formula  P  =  C  X  T  -~  D. 

p  =  pressure  in  Ibs.  per  sq.  in.,  T  =  thickness  in  inches,  C  =  a  con- 
stant, as  below. 


BOILER  DESIGN  AND  CONSTRUCTION. 


437 


Leeds  suspension  bulb  furnace C  =  17,000,  T  not  less  than  &  in. 

Morison  corrugated  type C  =  15,600,  T  not  less  than  ^  in. 

Fox  corrugated  type C  =  14,000,  T  not  less  than  &  in. 

Purves  type,  rib  projections C  =  14,000,  T  not  less  than  •&  in. 

Brown  corrugated  type C  =  14,000,  T  not  less  than  ^  in. 

Type  having  sections  18  ins.  long . .   C  =  10,000,  T  not  less  than  &  in. 

Limiting   dimensions   from   center   of   the   corrugations   or   pro- 
jecting ribs,  and  of  their  depth,  are  given  for  each  furnace. 

Tube  Spacing  in  Horizontal  Tubular  Boilers . — In  modern  practice 
the  tubes  are  arranged  in  vertical  and  horizontal  rows  (not  staggered 
as  in  earlier  practice),  with  not  less  than  1  in.  space  between  adjacent 
tubes,  not  less  than  2  ins.  between  the  two  central  vertical  rows,  and 
not  less  than  2J  in.  between  the 
shell  and  the  nearest  tube.  In 
boilers  60  in.  diameter  and  larger 
a  manhole  is  put  in  the  front 
head  beneath  the  central  rows  of 
tubes.  Fig.  173  (from  J.  T. 
Ryerson  &  Son,  Chicago)  shows 
the  arrangement  of  tubes  and 
also  of  the  braces  in  a  72  in. 
boiler. 

Fig.  174  shows  how  the  tubes 
are   arranged   in   some   styles   of 

vertical  tubular  boiler  in  order  to  facilitate  the  cleaning  of  scale  from 
the  tubes  and  crown-sheet. 

Manholes  and  Handholes. — Manholes  are  usually  made  11x15  in., 


Manhole 


FIG.  174. — RADIAL  ARRANGEMENT  IN 
TUBES  IN  A  VERTICAL  BOILER. 


FIG.  175.— FLANGED  MANHOLE.     FIG.  176. — MANHOLE  AND  HANDHOLE  PLATES. 

of  elliptical  shape.     The  metal  around  them  should  be  reinforced, 
either  by  riveting  on  it  an  elliptical  ring,   or  by  flanging.     The 


438  STEAM-BOILER  ECONOMY. 

sectional  area  of  the  reinforcing  ring  should  not  be  less  than  that 
of  the  portion  of  the  plate  removed  in  making  the  manhole,  measured 
through  its  longer  axis.  Handholes  are  of  the  same  shape  as  man- 
holes, and  are  usually  made  about  4x6  in.  They  should  always  be 
reinforced.  Various  methods  of  reinforcing  are  shown  in  Figs.  175 
and  176. 

Rule  for  Reinforcing.  (Hartford  Steam  Boiler  Insurance  and 
Inspection  Co.) — To  find  the  least  allowable  proportions  of  a  re- 
inforcing ring,  multiply  the  thickness  of  the  plate  by  the  length 
of  the  stock-hole;  this  gives  the  sectional  area  of  plate  cut  away  in 
making  the  hole.  The  total  sectional  area  of  the  reinforcing  ring 
must  be  at  least  as  great  as  this,  and  the  material  of  the  ring  must 
be  as  good  as  the  material  of  the  shell  plates.  The  width  of  the  re- 
inforcing ring  is  usually  limited  by  circumstances,  but  when  the 
width  has  been  decided,  the  thickness  of  the  ring  may  be  determined 
as  follows:  If  there  are  two  rings,  one  inside  and  one  outside  as 


FIG.  177. — RE-INFORECMENT  OF  MANHOLE. 

we  recommend,  and  as  is  shown  in  Fig.  177,  the  thickness  of  each 
ring  is  found  by  dividing  the  sectional  area  of  the  ring  by  four 
times  its  width.  (If  only  one  ring  is  used,  its  thickness  must  be 
equal  to  the  combined  thickness  of  the  two  rings  shown  in  Fig.  177. 

Rules  of  the  United  States  Board  of  Supervising  Inspectors: 
When  holes  exceeding  six  inches  in  diameter  are  cut  in  boilers  for 
pipe  connections,  man  and  handhole  plates,  such  holes  shall  be 
reinforced  with  wrought  iron  or  steel  rings  of  sufficient  width  and 
thickness  of  material  to  equal  the  amount  of  material  cut  from  such 
boilers,  except  that  when  holes  are  cut  in  any  flat  surface  of  such 
boilers,  and  such  holes  are  flanged  inwardly  to  a  depth  of  not  less 
than  1^  inches,  measuring  from  the  outer  surface,  the  reinforce- 
ment rings  may  be  dispensed  with. 

Massachusetts  Rule  for  Manholes. — A  manhole  shall  be  located  in 
the  front  head,  below  the  tubes,  of  a  horizontal  return-tubular  boiler 
60  in.  or  over  in  diameter.  A  manhole  or  handhole  shall  be  located  in 
the  front  head,  below  the  tubes,  of  a  horizontal  return-tubular  boiler 
less  than  60  in.  in  diameter.  A  handhole  shall  be  located  in  the  rear 
head  of  a  horizontal  return-tubular  boiler,  below  the  tubes,  except 
one  which  has  a  manhole  in  the  front  head,  below  the  tubes. 

Dimensions  of  Boilers. — The  tables  on  pages  439  and  440  give  the 
principal  dimensions  of  standard  forms  of  horizontal  return-tubular 
boilers  and  of  vertical  tubular  boilers. 


BOILER  DESIGN  AND  CONSTRUCTION. 


439 


Return-tubular  Boilers.     Standard  Dimensions.    (Coatesville  Boiler  Works.) 


Number 
of  Sizes. 

Horse- 
power. 

Diameter, 
inches. 

II 

a> 

Thickness 
of  Shell. 

Thickness 
of 
Heads. 

Number 
of  3-inch 
Tubes. 

"o    ^  M 

fill 

fill 

B 

Diameter 
of  Stack, 
inches. 

Thickness 
of  Stack 
B.G.No. 

1 

15 

36 

8 

1A 

H 

26 

2786 

2700 

30 

14 

16 

2 

20 

36 

10 

y* 

26 

3328 

2700 

30 

14 

16 

3 

25 

42 

10 

% 

36 

4458 

2900 

30 

16 

16 

4 

30 

44 

10 

A 

% 

42 

4750 

3500 

40 

18 

16 

5 

35 

44 

12 

% 

42 

5246 

3700 

40 

18 

16 

6 

40 

44 

14 

A 

y* 

42 

5790 

4000 

40 

18 

16 

7 

40 

48 

12 

A 

7 

IT 

48 

6122 

4300 

40 

18 

16 

8 

45 

48 

14 

A 

A 

48 

6832 

4300 

40 

20 

16 

9 

50 

48 

16 

A 

48 

7507 

4400 

40 

20 

16 

10 

55 

54 

12 

A 

A 

64 

8100 

4500 

40 

23 

16 

11 

60 

54 

14 

A 

A 

64 

8700 

4600 

40 

23 

16 

12 

70 

54 

16 

A 

A 

64 

10000 

4800 

50 

23 

14 

13 

60 

60 

12 

1 

A 

82 

9020 

4900 

45 

26 

10-12 

14 

70 

60 

14 

H 

A 

82 

10264 

5000 

45 

26 

10-12 

15 

80 

60 

16 

H 

A 

82 

11355 

5100 

50 

26 

10-12 

16 

95 

60 

18 

H 

A 

82 

12327 

5300 

60 

26 

10-12 

17 

90 

66 

14 

*/8 

98 

12203 

6200 

50 

28 

10-12 

18 

100 

66 

16 

i* 

98 

13498 

6400 

55 

28 

10-12 

19 

125 

66 

18 

% 

98 

14679 

6600 

60 

28 

10-12 

20 

100 

72 

14 

A 

y*. 

120 

15000 

6900 

50 

32 

10-12 

21 

125 

72 

16 

A 

y*. 

120 

16500 

7100 

60 

32 

10-12 

22 

150 

72 

18 

A 

¥ 

120 

17700 

7300 

60 

32 

10-12 

23 

175 

72 

20 

A 

120 

19500 

7500 

60 

36 

10-12 

24 

175 

78 

18 

A 

A 

20000 

8000 

60 

36 

10-12 

25 

200 

78 

20 

A 

2 

22000 

8200 

60 

36 

10-12 

Dimensions  of  Vertical  Tubular  Boilers. 


STAN&ARD 

SUBMERGED  TUBE. 

i 

Shell. 

Furnace. 

2-in.Tubes 

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440  STEAM-BOILER  ECONOMY. 

Standard  Vertical  Boilers.     (Coatesville  Boiler  Works.) 


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Fittings  comprise  one  steam  gage,  three  gage  cocks,  one  glass  water 
gage,  one  safety  valve,  one  check  valve,  one  blow-off  cock.  All  boilers 
are  tested  to  150  pounds,  hydrostatic  pressure.  Discounts  on  application. 

Dimensions  of  Marine  Water-tube  Boilers. — The  following  table 
of  the  weight  and  space  occupied  by  various  makes  of  marine  water- 


A 

Kind  of  Boilers. 

Heating 
Surface. 

sq.ft. 

Length, 
ft.     in. 

Width, 
ft.     in. 

Height. 
ft.     in. 

Outside 
Diameter 
of  Tubes, 
in. 

1 

Babcock    &     Wilcox      (U.S.S. 
Utah)  8  ft.  tubes  

5359 

9       1 

18       4 

13     11 

2  &  4 

2 

3 

4 

5 

Babcock     &     Wilcox     (U.S.S. 
New  Hampshire)  9  ft.  tubes 
Normand  (T.B.D.  Trippe)  
Normand,      modified     (U.S.S. 
Salem)  
Normand,      modified      (U.S.S. 
Chester)  

3926 
4780 

3166 
2670 

10       1 
12       6 

9     11 
10       8 

14     10 
15       1 

12        0 
12       8 

13        2 
14        2 

12        2 
11      10 

2    &  4 

1    &  1% 

iys 

154 

6 

7 
g 

9 
10 

Mosher  (U.S.S.  Kearsatge)  .... 
Thornycroft  (T.B.D.  Terry)  .  .  . 
White-Forster  (T.B.D.   Mary- 
ant)  ».  
Yarrow  (T.B.D.  Sterrett)  
Thornycroft  (T.B.D.  Burrows) 

3980 
4500 

4500 
4500 
4800 

12        2 
10       9 

9       1 
12       9 
12       7 

15       2 
15        3 

14       8 
14        2 
15        3 

12       9 
12        2 

12       8 
12      10 
12        6 

2 
IX  &  l*/s 

i    &  iy8 
i    &  \% 
\Yi&  iy8 

BOILER  DESIGN  AND  CONSTRUCTION. 


441 


Sq.    ft.    of 

Sq.    ft.    of 

Weight 
of  boiler 

1 

Kind  of  Boiler. 

Gage 
of  Tubes. 
B.  W.  G. 

Floor 
Space. 

Cubic 
Space. 

H.   S.   per 
sq.ft.  of 
Floor 

H.   S.   per 
cu.  ft.  of 
Cubic 

and  water 
per  sq.  ft. 
we 

§ 

. 

Space. 

Space. 

H.  o. 
pounds. 

fc 

No. 

sq.  ft. 

cu.  ft. 

/  1 

Babcock     &     Wilcox     (U.S.S. 

Utah)  8  ft.  tubes 

8  &  6 

167.7 

2337 

31.96 

2.293 

*28  .  70 

2 

Babcock     &     Wilcox      (U.S.S. 

New  Hampshire)  9  ft.  tubes 

8&  6 

150.0 

1978 

26.18 

1.985 

*25.80 

3 

Normand  (T.B.D.  Trippe)  .... 

12  &  10 

188.6 

2672 

25.35 

1.789 

f!2.40 

4 

Normand,      modified      (U.S.S. 

Salem)  

11 

119.4 

1453 

26.51 

2.179 

*13.10 

5 

Normand.      modified      (U.S.S. 

Chester)   

10 

134  7 

1592 

19.82 

1   678 

*17.64 

6 

Mosher  (U.S.S.  Kearsarge)..  .  . 

8 

184.2 

2349 

21.60 

1.695 

*23  .  00 

7 
8 

Thornycroft  (T.B.D.  Terry)  .  . 
White-Forster    (T.B.D.  Mary- 

12  &  10 

164.3 

1997 

27.31 

2.254 

f!2.20 

ant) 

12  &  10 

133.3 

1688 

33.74 

2.665 

fl2.10 

9 

Yarrow  (T.B.D.  Sterrett)  .... 

12  &  10 

181.0 

2323 

24.86 

1.937 

f!2.50 

10 

Thornyoroft  (T.B.D.  Burrows) 

11  &  10 

192.9 

2422 

24.88 

1.982 

t!3.23 

j  *  Includes  grates — coal  burning.  t  No  grates — oil  burning. 

Weights  are  for  boilers  and  fittings  with  water,  and  do  not  include  uptakes  and  funnels. 

tube  boilers  is  given  by  Rear-admiral  G.  W.  Melville,  II.  S.  N".  (Eng. 
Mag.,  Jan.,  1912). 

Sizes  of  Water-tube  Boilers. — Water-tube  boilers  are  commonly 
made  with  4-in.  tubes;  some,  such  as  the  Heine  boiler,  are  made  with 
3|-in.,  and  the  Babcock  &  Wilcox  marine  type  are  made  with  the 
bottom  row  4-in.  and  all  the  others  2-in.  tubes.  The  length,  number, 
spacing  and  arrangement  of  the  tubes  vary  greatly  according  to  the 
style  of  boiler  and  the  size  and  shape  of  the  space  it  is  designed  to 
occupy.  In  calculating  the  heating  surface  of  a  water-tube  boiler  of 
the  ordinary  types,  with  straight  tubes,  the  following  table  will  be 
found  convenient : 

HEATING    SURFACE    OF  BOILER   TUBES,    2,    3^    AND    4-IN.    DIAMETER. 


Length  of  Tubes,  Feet. 


Tubes  in. 

8 

10 

12 

14 

16 

18 

20 

Heating  Surface  of  One  Tube,  Sq.ft. 

2 

3^ 

4.189 
7.330 
8.378 

5.236 
9.163 
10.472 

6.283 
10.996 
12.566 

7.330 

18.828 
14.661 

8.378 
14.661 
16.755 

9.425 
16.493 
18.850 

10.472 
18.326 
20.944 

In  the  standard  form  of  inclined  tube  boiler,  with  4-in.  tubes, 
the  length  of  the  tubes  is  commonly  made  18  ft.,  and  the  number  of 
tubes  in  a  horizontal  row,  according  to  the  size  of  the  boiler,  is  4, 
5,  6  or  7  with  one  longitudinal  steam  and  water  drum,  8,  10,  12  or 


442 


STEAM-BOILER  ECONOMY. 


14  with  two  drums,  and  21  with  three  drums.  The  number  of 
horizontal  rows  is  7,  8;  9,  10,  12  or  14.  The  number  of  tubes  and 
the  total  heating  surface  of  the  tubes  in  these  arrangements,  together 
with  the  corresponding  area  of  grate  surface,  are  given  below : 

HEATING    SURFACE    OF   WATER-TUBE    BOILERS. 


Tubes 
High. 

Number  of  Tubes  Wide. 

4 

5 

6 

7 

8 

10 

12 

14 

21 

Total  Number  of  Tubes. 

7 

28 

35 

42 

49 

56 

70 

84 

98 

147 

8 

32 

40 

48 

56 

64 

80 

96 

112 

168 

9 

36 

45 

54 

63 

72 

90 

108 

126 

189 

10 

40 

50 

60 

70 

80 

100 

120 

140 

210 

12 

48 

60 

72 

84 

96 

120 

144 

168 

252 

14 

56 

70 

84 

98 

112 

140 

168 

196 

294 

Total  Heating  Surface,  with  Tubes  18  Feet  Long. 

7 

528 

660 

792 

924 

1056 

1319 

1583 

1847 

2771 

8 

604 

754 

905 

1056 

1206 

1508 

1810 

2111 

3167 

9 

690 

848 

1018 

1188 

1357 

1696 

2036 

2375 

3563 

10 

754 

942 

1131 

1319 

1508 

1885 

2262 

2639 

3958 

12 

905 

1131 

1357 

1583 

1810 

2262 

2714 

3166 

4750 

14 

1056 

1319 

1583 

1847 

2111 

2639 

3167 

3694 

5542 

Grate  Surface,  7  Feet  Long.  Square  Feet. 

"16.3 

20.4 

24.5 

28.6 

32.7 

40.8 

49.0 

57.2 

85.7 

The  water  and  steam  drums  are  usually  made  30,  36,  42  or  48  in. 
diameter,  and  of  lengths  ranging  from  6  to  20  ft.,  according  to  the 
size  of  the  boiler  and  according  to  whether  the  drum  is  placed  length- 
wise or  crosswise  of  the  boiler.  Taking  the  heating  surface  as  that  of 
the  lower  half  of  the  drum,  the  following  table  gives  the  heating  sur- 
face of  drum  of  the  several  sizes  named : 


Length,  tft. 


20 


Diam.,  ins. 

Heating  Surface  of  Lower  Half  of  Drum,  sq.ft. 

30 

24 

31 

39 

47 

55 

63 

71 

79 

36 

28 

38 

47 

57 

66 

75 

85 

94 

42 

33 

44 

55 

66 

77 

88 

99 

110 

48 

38 

50 

63 

75 

88 

101 

113 

126 

Specifications  for  Horizontal  Tubular  Boiler  and  Boiler-room 
Equipment.  (Charles  L.  Hubbard,  in  Power,  Dec.  1905.) — The  ap- 
pended "dummy"  has  been  found  useful  in  making  up  specifications 
for  tubular  boilers,  together  with  their  settings.  Under  each  heading 
will  be  found  numbered  clauses  to*  fit  all  usual  cases,  and  such  of 
these  may  be  chosen  as  are  necessary  to  meet  the  conditions  of  any 


BOILER  DESIGN  AND  CONSTRUCTION.  443 

particular  instance.  For  example,  under  "Braces,"  No.  1  calls  for 
the  usual  crowfoot  bracing;  Nos.  3  and  4,  or  3  and  5,  call  for 
through-bracing,  and  Nos.  1,  2  and  4  a  combination  of  the  two. 

In  making  up  a  specification  the  engineer  has  simply  to  check 
off  the  clauses  he  wishes  to  use  under  the  different  heads,  fill  in  with 
pencil  the  spaces  left  for  dimensions,  etc.,  and  his  typewriter  operator 
may  do  the  rest.  Check  marks  and  writing  can  be  erased  afterward, 
and  the  dummy  used  again  and  again  a  number  of  times. 

Blank  spaces  are  filled  in,  in  the  following  specification,  in 
order  to  make  the  method  of  use  more  clearly  understood. 

SPECIFICATIONS  FOR  BOILERS. 

Type  and  General  Dimensions. — The  boilers,  2  in  number,  are 
to  be  of  the  horizontal  tubular  type,  with  full  overhanging  fronts,  and 
all  parts  and  pieces  must  be  designed  accordingly. 

The  shells  are  to  be  16  feet  6  inches  long  outside,  and  60 
inches  in  diameter,  measured  on  the  outside  of  the  smallest  ring  of 
plates. 

The  heads  are  to  be  15  feet  0  inches  apart  outside.  The 
size  and  description  of  the  other  parts  are  to  conform  substantially 
to  the  details  usually  furnished  by  the  In- 

spection and  Insurance  Company  for  boilers  of  this  size,  and  during 
the  process  of  construction  all  the  material  and  workmanship  en- 
tering into  the  same  are  to  be  subjected  to  the  inspection  of  the  en- 
gineer and  a  representative  of  said  company. 

Materials;  Quality  and  Thickness. — (1)  Shell  plates  are  to  be 
%  of  an  inch  in  thickness,  of  open-hearth  fire-box  steel,  having 
a  tensile  strength  of  not  less  than  54,000  nor  more  than  60,000 
pounds  per  square  inch,  with  not  less  than  56  per  cent  as  con- 
traction of  area,  and  an  elongation  of  25  per  cent  in  length  of  8 
inches. 

(2)  Phosphorus  to  be  less  than  0.03  per  cent  and  sulphur  less 
than  0.025  per  cent.* 

(3)  A  coupon  two  inches  Avide  is  to  stand  bending  180.  degrees 
on  itself  without  showing  signs  of  fracture,  both  before  and  after 
heating  to  a  cherry-red  and  quenching  in  water. 

(4)  A   sworn   certificate  is   to  be  furnished  by  the  plate   mill 
that  each  heat  of  metal  used  for  the  plates  has  been  tested  and  ful- 
filled  the    chemical   tests,   and   that   the    coupon    from   each   plate 
has  been  tested  and  has  come  up  to  the  physical  requirements.    With 
and  as  a  part  of  the  certificate  shall  be  furnished  a  schedule  of  the 
samples  tested  and  the  data  determined  by  the  tests. 

*  The  Hartford  Steam  Boiler  Inspection  and  Insurance  Co.  allows  0.035 
phosphorus  and  0.035  sulphur.  The  Pennsylvania  Railroad  Co.'s  specifica- 
tions for  fire-box  steel  allow  0.035  P  and  0.003  S.  American  Bureau  of  Shipping's 
specifications  for  marine  boilers  allow  for  shells  P  and  S  each  not  over  0.04; 
for  fire-boxes,  P  and  S  each  not  over  0.035. 


444  STEAM-BOILER  ECONOMY. 

(5)  Heads  to  be    %    inch  in  thickness  of  best  open-hearth  flange 
steel. 

(6)  All  plates,  both  of  shells  and  heads  are  to  be  plainly  stamped 
with  the  name  of  maker,  brand  and  tensile  strength.     The  marks 
shall  be  so  located  that  they  may  be  plainly  seen  on  each  plate  after 
the  boiler  is  constructed. 

Riveting. —  (1)  Longitudinal  seams  are  to  be  of  the  double- 
riveted  lap-joint  type  with  rivets  staggered.*  They  must  be  arranged 
to  come  well  above  the  fire  line  of  the  boilers,  and  must  break  joints 
in  different  courses  in  the  usual  manner. 

Rivets  to  be  13-16  inch  in  diameter  and  pitched  3  inches  on 
centers;  the  two  rows  to  be  2  inches  apart  on  centers. 

(2)  Longitudinal   seams  are  to   be  of  the  double-riveted   butt- 
joint   type   with   double   covering   strips.      They   must   be   arranged 
to   come   well   above   the   fire   line   of   the  boilers,   and   must  break 
joints  in  different  courses  in  the  usual  manner. 

Rivets  are  to  be  %  incn  *n  diameter;  those  of  the  inner  rows 
are  to  be  pitched  2  inches  apart. 

The  rivets  of  the  outer  rows  are  to  be  pitched  4  inches  on 
centers  and  the  rows  to  be  2^  inches  apart. 

The  covering  strips  are  to  be     %     inches  in  thickness. 

(3)  Longitudinal   seams   are   to   be   of   the   triple-riveted  butt- 
joint  type  with  double  covering  strips.     They  must  be  arranged  to 
come  well  above  the  fire  line  of  the  boilers,  and  must  break  joint,  in 
different  courses  in  the  usual  manner.     Rivets  are  to  be    %    inch  in 
diameter;  those  of  the  two  inner  rows  are  to  be  pitched     3J     inches 
on  centers,  and  the  rows  are  to  be  2%  inches  apart;  the  rivets  of 
the  two  intermediate  rows  are  to  be  pitched     3|     inches  on  centers 
and  the  rows  are  to  be  6f.  inches  apart,  while  the  rivets  of  the  two 
outer  rows  are  to  be  pitched     6-J     inches,  and  the  rows  are  to  be 
llf     inches  apart.     The  covering   strips  are  to  be     5-16     inch  in 
thickness. 

(4)  The  transverse  seams  are  to  be  single  riveted,  with  rivets 
13-16     inch  in  diameter  and  pitched     2     inches  on  centers. 

(5)  The  rivet  holes  must  be  drilled,  and  must  be  neatly  cham- 
fered    1-32     inch  on  the  faying  side  of  all  plates.     Care  must  be 
exercised  in  drilling  the  holes  that  they  come  fair  in  construction. 

(6)  The  use  of  the  drift  pin  to  bring  blind  or  partially  blind 
holes  in  line  will  be  sufficient  cause  for  the  rejection  of  the  boilers. 

Braces. —  (1)  Each  boiler  shall  have  8  solid  steel  crowfoot  braces 
attached  to  each  head  above  the  tubes  and  arranged  as  shown  on 
detail.  Each  brace  shall  have  a  sectional  area  of  not  less  than  1 
square  inch  at  its  weakest  part,  and  shall  be  riveted  to  the  head  and 
shell  with  two  1  inch  rivets  at  each  end. 

Braces  in  the  outer  row  shall  be     48     inches  in  length,  those 

*  The  lap  joint  for  longitudinal  seams  is  now  condemned  by  law  in  some 
States. 


BOILER  DESIGN  AND  CONSTRUCTION.  445 

in  the  second  row  60  inches  in  length,  and  those  in  the  third 
row  72  inches  in  length.  Care  must  be  exercised  in  setting  them 
so  that  they  shall  bear  a  uniform  tension. 

(2)  In  addition  to  the  crowfoot  braces  above  specified,  each  boiler 
shall  have    3    through  braces  of  mild  steel  of  a  tensile  strength  equal 
to  that  of  the  shell. 

Each  brace  shall  be  1£  inches  in  diameter  and  without  welds. 
The  ends  shall  be  upset  to  2  inches  and  shall  be  provided  with 
nut,  check-nut  and  heavy  cast-iron  washer,  one  inch  in  thickness 
and  5  inches  in  diameter,  planed  or  milled  on  both  sides. 

(3)  Each  boiler  shall  have     5     through  braces   of  mild  steel 
of  a  tensile  strength  equal  to  that  of  the  shell. 

Each  brace  shall  be  1%  inches  in  diameter  and  without  welds. 
The  ends  shall  be  upset  to  2  inches  and  shall  be  provided  with  nut, 
check-nut  and  heavy  cast-iron  washer,  one  inch  in  thickness  and  5 
inches  in  diameter,  planed  or  milled  on  both  sides. 

Care  must  be  exercised  in  setting  them,  so  that  they  shall  bear 
uniform  tension. 

(4)  The  boiler  heads   are  to   be   stiffened    with     6     inch    by 
2.39     inch  by     0.52     inch  channel  bars  riveted  to  the  heads  and 
arranged  as  shown  on  detail- 

( 5 )  The  boiler  heads  are  to  be  stiffened  with    3    inch  by    3    inch 
by     !/2    inch  angle  bars  riveted  to  the  heads  and  arranged  as  shown 
on  detail. 

Tubes:  (1)  Each  boiler  is  to  have  72  best  lap-welded  tubes 
3  inches  in  diameter  and  15  feet  long,  set  in  vertical  and  horizon- 
tal rows,  with  a  clear  space  between  them  vertically  and  horizontally 
of  one  inch,  except  the  central  vertical  space,  which  is  to  be  2 
inches. 

The  holes  for  the  tubes  are  to  be  neatly  chamfered  off  on  the 
outside. 

(2)  The  tubes  are  to  be  set  with  a  expander  and 

beaded  down  at  each  end. 

Manhole:  Each  boiler  is  to  have  one  manhole,  11x15  inches, 
with  a  strong  internal  frame,  made  of  "gun"  iron  or  sound  steel 
casting,  with  suitable  plate,  yoke  and  bolt,  the  proportions  of  the 
whole  to  be  such  as  will  make  it  as  strong  as  any  portion  of  the 
shell  of  like  area.  It  is  to  be  located  in  the  shell  on  top  of 
boiler. 

Handholes:  Each  boiler  is  to  have  one  handhole,  4x6  inches, 
with  suitable  plate,  yoke  and  bolt,  located  in  each  head,  below  the 
tubes. 

Brackets  and  Wall  Plates:  (1)  Each  boiler  is  to  have  4  cast- 
iron  brackets,  2  on  each  side,  securely  riveted  in  place,  12  inches 
long,  with  a  projection  of  10  inches  from  the  shell. 

(2)  Cast-iron  wall  plates  20  inches  long,  and  10  inches 
wide  and  1J  inches  thick  shall  be  furnished  for  each  bracket  to 
rest  upon,  and  three  rollers  1  inch  in  diameter  and  9  inches 


446  STEAM-BOILER  ECONOMY. 

long  shall  be  furnished  for  all  except  the  front  brackets,  to  rest  upon 
to  allow  free  expansion  of  the  boiler. 

Nozzles. — Each  boiler  is  to  have  two  nozzles  of  "gun"  iron  or 
cast  steel,  5  inches  in  diameter  for  steam-pipe  connection,  and 
one  4  inches  in  diameter  for  safety-valve  connection,  each  ac- 
curately squared  on  top  flange,  and  securely  riveted  to  the  boiler. 
These  flanges  are  to  be  trued  to  the  plane  of  the  tubes,  and  must 
receive  the  approval  of  the  engineer  in  this  regard  before  the  boilers 
are  set. 

Smoke  Opening. — Each  boiler  is  to  have  an  opening  12  inches 
by  38  inches  cut  out  of  front  connection  (on  top)  for  the  at- 
tachment of  uptake  or  bonnet. 

Internal  Feed  Pipe. — Each  boiler  is  to  have  a  hole  tapped  to  re- 
ceive a  1J  inch  feed-pipe.  This  is  to  be  located  at  the  front 
head  at  the  point  indicated  on  details;  also  furnish  and  put  in  a 
1J  inch  brass  feed-pipe,  extending  from  front  head  back  to  within 
two  feet  of  the  rear  head  of  the  boiler,  thence  across  the  end  to 
an  elbow  looking  down  between  the  tubes  and  shell.  The  pipe  shall 
be  securely  supported  by  hangers  attached  to  the  braces. 

Blow-off. —  (1)  Each  boiler  is  to  have  a  circular  plate  of  the 
same  material  as  the  shell,  8  inches  in  diameter  and  five-eighths 
inch  thick,  riveted  to  the  bottom  of  the  shell,  9  inches  from  the  back 
end,  and  tapped  to  receive  a  2  inch  blow-off  pipe. 

(2)  The  blow-off  pipes  are  to  be  extra  heavy,  with  extra  heavy 
fittings,  and  are  to  be  carried  straight  down  through  the  paving  of 
the  combustion  chamber.     That  portion  exposed  in  the  combustion 
chamber  is  to  be  protected  by  a  cast-iron  sleeve  packed  with  mineral 
wool. 

(3)  These  pipes  are  to  be  extra  heavy,  with  extra  heavy  fittings, 
and  are  to  be  carried  straight  down  through  the  paving  of  the  com- 
bustion chamber;  they  are  to  be  protected  on  the  side  toward  the 
furnace  by  means  of  a  V-shaped  shield  of  fire-brick  laid  in  either 
a  mixture  of  fire-clay  and  ground  fire-brick,  or  in  pure  cement,  and 
extending   from   the   paving  to  the   boiler  shell. 

Fusible  Plug. — The  boilers  are  each  to  be  provided  with  a  high- 
pressure,  long  fusible  plug  in  the  back  head  with  its  center  two 
inches  above  the  top  of  the  upper  row  of  tubes. 

Fittings. —  (1)  Furnish  and  properly  connect  to  each  boiler  one 
8  inch  steam  gage  with  nickel-plate  rim  and  iron  body  of  the 

or   other   approved   make,   graduated   for    indicating 
pressures  up  to  a  maximum  of  100  pounds  per  square  inch. 

(2)  Furnish  and  connect  to  each  boiler  one     3-|     inch 

or  other  equally  approved  make,  pop  safety  valve,  set  to  blow  at 
a  pressure  of  70  pounds  per  square  inch. 

(3)  Furnish  and  connect  with  each  boiler  one    4    inch 

or  other  equally  approved  lever  safety  valve  of  best  make,  and  set 
to  blow  at  a  pressure  of  70  pounds. 

(4)  Provide  suitable  chain  and  pulley  attachments  for  lifting 


BOILER  DESIGN  AND  CONSTRUCTION.  447 

the  safety  valves  and  carry  the  pull  chains  to  such  convenient  point 
for  use,  as  shall  be  directed  by  the  engineer. 

(5)  Connect  each  safety  valve  with  a    3^     inch  pipe  and  carry 
the  same  out-of-doors,  as  directed  for  discharge. 

(6)  This  pipe  is  to  be  dripped  to  the  ash-pit  through  a     % 
inch  connection  if  found  necessary  by  the  engineer. 

(7)  Furnish  and  connect  with  each  boiler  one  combination  box 
with  a     %     inch  gage  glass,  and  three  gage  cocks;  the  boiler  con- 
nections are  to  be  of     1£     inch  brass  pipe  outside  the  smoke  bon- 
net and  extra  heavy  wrought  iron  of  the  same  size  inside  the  bonnet. 

A  %  inch  brass  drip  pipe  with  valve  is  to  be  carried  to  the 
ash-pit. 

Set  the  water  gage  at  such  a  level  that  there  shall  be  two  inches 
of  water  over  the  top  of  the  tubes  when  the  water  disappears  from 
the  bottom  of  the  glass. 

Castings,  Doors,  Bolts,  etc. —  (1)  Each  boiler  shall  be  provided 
with  a  cast-iron  front,  neatly  made  and  close  fitting,  and  erected  in 
strict  accordance  with  directions  to  be  given  by  the  engineer;  all 
necessary  anchor  bolts  10  feet  long;  close-fitting  front  connection 
doors,  with  suitable  fastenings  to  prevent  warping;  2  furnace  doors 
with  liner  plates;  2  ash  doors;  back  connection  door,  16x24  inches, 
with  liner  plates;  all  doors  to  be  made  easily  closing  and  tight 
fitting. 

(2)  Arch  bars  for  back  connection  and  all  buckstaves,  with  the 
necessary  bolts  or  tie-rods;  and  all  other  castings  or  iron  work  of 
any  description  necessary  for  the  proper  setting  of  the  boilers  com- 
plete. 

Grates. —  (1)  Provide  and  install  grate-bars  for  plain  grates  of 
the  ,  or  other  approved  pattern,  60  inches  long  by 

54  inches  wide  with  suitable  bearer  bars  for  the  same.' 

(2)  Provide  and  install  complete  for  operation,  shaking  grates 
of  the  ,  ,  or  other  approved  make,  60  inches 

long  by  54  inches  wide. 

Inspection  and  Insurance. — The  size  and  description  of  all  parts 
to  conform  subtantially  to  the  details  usually  furnished  for  boilers 
of  this  size,  and  during  the  process  of  construction  all  the  material 
and  workmanship  are  to  be  subject  to  the  inspection  of,  and  after 
erecting  to  be  approved  by,  the  engineer  and  by  the  In- 

spection and  Insurance  Company,  and  the  latter's  insurance  policy 
for  $1000  on  each  boiler  for  3  years  from  completion  of  setting 
to  be  furnished  the  owners  by  the  contractor. 

Tests. — Before  leaving  the  construction  shops,  each  boiler  shall 
be  tested  under  a  hydrostatic  pressure  of  150  pounds  to  the  square 
inch,  and  all  joints  and  all  connections  made  tight  at  that  pressure. 

Should  leaks  develop  under  pressure  when  first  applied,  the 
pressure  shall  be  removed  and  all  leaks  stopped  by  calking,  after 
which  the  boiler  must  again  be  subjected  with  satisfactory  results 
to  the  pressure. 


448  STEAM-BOILER  ECONOMY. 

All  tests  shall  be  made  in  the  presence  of  a  representative  of  the 
aforesaid  insurance  company  and  of  the  engineer. 

Boiler  Foundations. —  (1)  The  boiler  foundations  will  be  fur- 
nished under  another  contract. 

(2)  The  boiler  foundations  are  to  be  furnished  by  the  contractor, 
and  shall  be  of  concrete  or  of  stone,  laid  in  pure  cement.     If  con- 
crete is  used,  it  shall  consist  of  one  part  best  Portland  cement,  two 
parts  of  clean,  sharp  sand  and  four  parts  of  broken  stone.     They 
shall  extend  a  distance  of  not  less  than    30    inches  below  the  boiler- 
room  grade,  or  shall  be  carried  to  such  depth  as  the  engineer  shall 
direct  in  order  to  secure  a  proper  footing. 

( 3 )  The  width  of  foundation  for  the  different  walls  of  the  setting 
shall   be   as   follows:    Outside   walls,    42   inches;    division   walls      4 
inches;   front   wall,     24      inches;   bridge   wall,      24      inches;   rear 
wall,     42     inches. 

(4)  The  foundation  shall  be   in  the   form   of  a  solid   bed,   20 
feet,     0     inches  long,  by     18     feet     10     inches  wide,  and  of  the 
depth  specified  above. 

Boiler  Settings. —  (1)  The  boiler  settings  are  to  be  built  sub- 
stantially, as  shown  on  plans. 

(2)  The  settings  are  to  be  of  the  usual  form  employed  for  this 
type  of  boiler. 

(3)  Inside  bricks  are  to  be  light-hard;  exposed  or  outside  bricks 
are  to  be  best  quality  hard-burned. 

(4)  Furnace,   bridge   wall   and   combustion   chamber   are   to   be 
lined    with   Al    firebrick. 

(5)  Furnace,  bridge  wall  and  arch  over  combustion  chamber  are 
to  be  lined  with  Al  fire-brick. 

(6)  The  outside  walls  are  to  be     22     inches  in  thickness,  made 
up  of  a    12    inch  inside  wall,  a    2    inch  air-space,  and  an    8    inch 
outside  wall ;  division  wall,    2    inches ;  front  wall,    9    inches ;  bridge 
wall,     24     inches;   and   rear   wall,     18      inches,   made   up   of   two 
8-inch  walls,  with  a  2-inch  air-space  between.     The  distance  from 
bridge  wall  to  boiler  shell   shall  be     9     inches. 

(7)  All  red  bricks  are  to  be  laid  in  cement  mortar  of  best  qual- 
ity, mixed  the  day  it  is  to  be  used.     Fire-bricks  are  to  be  laid  either 
in  a  mixture  of  fire-clay  and  ground  fire-brick,  or  in  pure  cement, 
with  very  close  joints. 

(8)  The  boiler  tops  are  to  be  covered  with  one  layer  of  light- 
burned  brick,  laid  loose  on  side,  care  being  taken  to  leave  a  clear 
space  about  the  rivet  heads,  and  an  outer  cover  similarly  laid  in 
cement  mortar. 

(9)  The  entire  surface   of  the  boiler  setting  is  to  be  covered 
with  two  coats  of  freshly  made  cement  wash,  colored  to  resemble 
brick  and  applied  with  a  brush.     This  wash  is  to  be  applied  near  the 
completion  of  the  contract,  and,  before  it  is  done,  all  cracks  and 
openings  in   the   setting  shall  be   pointed.     If  any   portion  of  the 
setting  has  become  loosened  by  the  expansion  of  the  boilers  it  shall 


BOILER  DESIGN  AND  CONSTRUCTION.  449 

be  removed  and  the  bricks  relaid  in  a  manner  satisfactory  to  the 
engineer. 

Smoke  Connection. —  (1)  Smoke  connections  are  to  be  made  of 
No.  12  American  gage  black  iron  of  the  sizes  indicated,  and  are 
to  be  run  as  shown  on  plans.  So  far  as  practicable,,  all  rectangular 
parts  are  to  be  made  with  internal  angle  irons,,  to  which  the  plates 
are  to  be  riveted,  and  all  joints  are  to  be  made  tight  with  suitable 
filling,  if  found  necessary. 

All  joints  between  boilers  and  uptakes  are  to  be  neatly  and  tightly 
made  by  means  of  angles  bolted  to  the  shells  and  uptakes.  Clean-out 
doors  are  to  be  provided  as  indicated  or  directed. 

(2)  A  damper  is  to  be  placed  in  each  uptake  or  bonnet  for  hand 
regulation,  and  suitable  and  approved  means  are  to  be  approved  for 
adjusting  and  securing  it  in  any  desired  position. 

(3)  Furnish  and  place  in  the  main  smoke-pipe  a  balanced  damper 
of  No.     10     iron,  closing  at  an  angle  of     45     degrees,  and  provide 
the  same  with  roller  bearings  for  easy  movement.     This  damper  is 
to  be  connected  with  a  damper  regulator  to  be  specified  later. 

Damper  Regulator. — Furnish  and  properly  connect  to  the  steam 
main,  water  pressure  and  main  damper  a  ,  ,  or  other  ap- 

proved damper  regulator  of  latest  pattern,  locating  the  same  in  the 
boiler-room  at  such  point  as  the  engineer  shall  direct.  Provide  all 
necessary  chains,  weights  and  pulleys  and  adjust  the  regulator  to 
close  the  damper  at  a  pressure  of  50  pounds  steam  pressure. 

Feed  Pipe. —  (1)  The  feed  pipe  to  the  boilers  should  be  of  brass, 
1J  inches  in  diameter,,  each  branch  to  be  furnished  with  a 

check  valve  and  gate  valve,  placed  inside  the 

check  next  to  the  boiler.  A  1J  inch  brass  connection  shall  be 
made  between  this  pipe  and  the  supply  main  inside  the  building. 

(2)    The  delivery  pipe  from  the  pumps  to  the  boilers  shall  be 
2     inches  in  diameter,  of  heavy  polished  brass,  with  polished  brass 
fittings,  and  run  substantially  as  shown  on  plans.     Each  branch  is  to 
be  furnished  with  a  check  valve,  finished  brass  union,  and 
gate  valve  placed  inside  the  check  next  to  the  boiler. 

That  portion  of  the  feed  pipe  within  the  smoke  bonnets  is  to 
be  of  extra-heavy  iron.  A  1£  inch  valved  connection  of  brass 
pipe  is  to  be  made  with  the  feed  pipe  between  the  pumps  and  boiler 
for  supplying  water  directly  from  the  street  main. 

Blow-off  Pipe. —  (1)  Provide  and  place  in  the  blow-off  pipe  from 
each  boiler  an  asbestos-packed  cock,  a  gate  valve  and 

flanged  union,  placing  the  gate  valve  inside  the  cock  next  to  the 
boiler.  Provide  wrenches  for  the  cocks. 

(2)  Provide  and  place  in  the  blow-off  pipe  from  each  boiler 
a  heavy  blow-off  valve,  made  by  ;  also  a  heavy 

flanged  union. 

Blow-off  Tank. —  (1)  Furnish,  place  and  connect,  in  a  complete 
and  proper  manner,  a  blow-off  tank  of  %  inch  boiler  iron,  heads 
to  be  5-16  inch  in  thickness  and  of  the  same  material.  The  tank 


450  STEAM-BOILER  ECONOMY. 

shall  be  36  inches  in  diameter  by  48  inches  in  length;  it  shall  be 
made  with  a  manhole  on  top  and  a  handhole  in  each  end,  each  to 
be  furnished  with  a  suitable  plate,,  yoke  and  bolt.  Provide  with  drain 
from  the  bottom  and  inlet  at  the  top,  so  designed  as  to  keep  the  tank 
continuously  full  of  water.  It  is  to  be  mounted  on  cast-  or  wrought- 
iron  cradles,  bolted  to  bluestone  or  slate  slabs,  mounted  on  brick 
foundations. 

Provide    and    connect    with    the    tank    a     24     inch    water-gage 
glass. 

(2)  Furnish,,  place  and  connect  in  a  complete  and  suitable  man- 
ner a  cast-iron  flow-off  tank,     24    inches  in  diameter  by    48     inches 
in  depth.     The  tank  is  to  have  a  cast-iron  head  and  is  to  be  fur- 
nished with  a  suitable  drain  from  the  bottom  and  inlet  at  the  top,  so 
designed  as  to  keep  it  continuously  full  of  water.     The  tank  is  to 
be  sunk  in  the  ground  to  a  depth  of    40    inches. 

Fire  Tools. — Furnish  complete  sets  of  fire  tools,  each  con- 

sisting of  slice-bar,  poker,  hoe,  steam- jet  flue  cleaner,  large-size  steel 
scoop  shovel,  long-handled  shovel  and  long  wooden-handled  hoe  of 
large  size  for  removing  ashes.  Provide  iron  racks  of  approved 
design  for  holding  the  tools  when  not  in  use. 

(3)  Furnish  one  coal  barrow  of     300     pounds  capacity,  made 
by  and  of  a  pattern  approved  by  the  engineer. 

(4)  Furnish  one  steel  coal  car  of     500     pounds  capacity,  made 
by  and  of  a  pattern  approved  by  the  en- 
gineer. 

(5)  Furnish  one    50    foot  length  of  best    %    inch  4-ply  rubber 
hose,  complete  with  coupling,  nozzle,  etc.     It  is  to  be  furnished  and 
mounted   on   an   iron  hose   rack  in  the  boiler-room.     Also   provide 
screw  bibbs  in  the  water-supply  pipe  at  convenient  points  for  the 
attachment  and  use  of  the  hose. 

Feed   Pumps. — (1)    Furnish      2      duplex,   brass-finished    boiler 
feed  pumps,      4J       by    2J    by    4    inches  in  size,  of  ,  , 

or  other  approved  make  of  equal  capacity.  Mount  the  pumps 
on  brick  foundations,  capped  with  bluestone  or  slate  slabs  of  suit- 
able size.  Make  all  steam  exhaust,  suction  and  discharge  connections, 
connect  all  drips  with  the  sewer,  and  provide  all  valve  and  fittings 
required  for  installing  the  pumps  in  a  complete  and  satisfactory 
manner,  ready  for  use.  Provide  and  connect  with  the  steam  pipe 
of  each  pump  a  or  other  approved,  brass  sight-feed  lubri- 

cator of  1  pint  capacity. 

(2)  Suitable  pans  of  heavy  copper,  of  a  size  to  accommodate 
the  bed  plates  of  the  pumps,  are  to  be  provided  for  catching  the 
leakage  of  water  and  oil.     These  are  to  be  dripped  to   the  sewer 
through  valved  drain  pipes  of  suitable  size. 

(3)  The  cast-iron  bed  plates  of  the  pumps  are  to  be  so  made 
as  to  form  a  drip  pan  for  catching  the  leakage  of  water  and  oil. 
These  are  to  be  dripped  to  the  sewer  through  valved  drain  pipes  of 
suitable  size. 


BOILER  DESIGN  AND  CONSTRUCTION.  451 

The  specifications  of  Mr.  Hubbard  agree  fairly  well  with  the 
printed  specifications  issued  by  the  largest  manufacturers  and  with 
those  of  the  boiler  inspection  and  insurance  companies.  The  speci- 
fications of  the  Bigelow  Co.,  New  Haven,  Conn.,  contain  some  items 
not  included  in  Mr.  Hubbard's  specifications,  and  also  some  differences 
of  detail,  such  as  quality  of  rivets,  machine-flanging  and  annealing 
of  heads,  and  pressed  steel  manhole  frames.  Some  paragraphs  from 
the  Bigelow  Co/s  specifications  are  given  below. 

Riveting. — All  holes  to  be  punched  %  of  an  inch  smaller  than 
the  diameter  of  the  rivet,  where  the  plates  are  to  be  bolted ,  together, 
and  each  and  every  rivet  hole  drilled  in  place,  1-16  of  an  inch 
larger  than  the  diameter  of  the  rivet.  No  rivets  to  be  driven  into 
unfair  holes.  Should  any  holes  be  in  the  least  unfair,  they  are  to 
be  brought  in  line  by  the  use  of  a  reamer  or  drill,  and  in  no  case 
will  a  drift  pin  be  used  for  this  purpose.  All  rivets,  where  possible, 
to  be  driven  by  hydraulic  pressure,  and  the  rivet  allowed  to  cool 
and  take  its  shrinkage  under  pressure. 

Rivets. — To  be  of  soft  steel,  having  tensile  strength  of  not  less 
than  52,000  pounds  per  square  inch  of  section,  and  elongation  of 
not  less  than  29  per  cent  in  8  inches. 

Flanging. — Heads  to  be  machine  flanged,  with  a  radius  of  2l/2 
inches,  and  after  they  have  been  bored  and  reamed  for  tubes  and 
rivets  are  to  be  put  into  the  furnace  and  thoroughly  annealed. 

Planing  and  Calking. — All  plates  to  have  proper  allowance  for 
planing,  and  to  be  planed  on  a  planing  machine  to  an  angle  of  about 
15  degrees  from  the  vertical.  The  heads,  after  they  have  been 
flanged,  drilled  and  annealed,  are  to  be  put  on  a  boring  mill  and 
edges  planed  to  the  same  bevel  as  the  shell  plates. 

All  seams  to  be  carefully  calked  with  a  round  nosed  tool. 

Holes  for  Tubes. — To  be  drilled  and  reamed  not  to  exceed     1-32 
of  an  inch  larger  than  the  diameter  of  the  tube,  and  neatly  cham- 
fered on  the  outside.    Tubes  set  with  a  Dudgeon  expander, 
on  each  end. 

Manholes. — Boiler  to  have  a  manhole  opening     11     inches 

by  15  inches,  with  a  double  riveted  internal  pressed  steel  frame 
located  on  top  of  shell,  with  a  suitable  pressed  steel  plate  with 
yoke  and  bolt  nicely  fitted,  the  proportions  of  the  whole  such  as 
will  make  it  equally  as  strong  as  any  other  portion  of  the  shell, 
of  like  area. 

Front  and  Castings  for  Setting. — Each  boiler  to  be  provided  with 
a  cast-iron  front  like  Plate  in  our  cata- 

logue, made  in  not  less  than  pieces,  exclusive  of  the  doors, 

fitted  and  fastened  together  with  angle  iron.  To  have  double 
flue,  fire  and  ash  doors  all  closely  fitted,  with  suitable  fastenings 
to  prevent  warping,  and  the  fire-doors  to  have  liner  plates 
bolted  on.  Front  to  have  all  necessary  anchor  bolts  feet 


452 


STEAM-BOILER  ECONOMY. 


long,  also  extra  heavy  arch  and  flat  plate  for  top   and  bottom  of 
fire-doors. 

Arch  plate  to  be  of  our  special  pattern,  with  removable  fire- 
brick lining  which  can  be  replaced  at  any  time  without  removing 
the  cast-iron  plate  itself  or  affecting  the  mason  work  in  any  way 
whatsoever.  Also  special  fire-brick  jambs  for  the  side  of  fire-doors. 

One  back  cleaning  door  18  inches  by  20  inches,  with  tee 
pieces  and  anchor  bolts  to  hold  the  same  in  the  brick-work. 

Three  special  patent  rear  arch  bars  for  back  connection,  made  to 
be  lined  with  fire-brick. 

Setting  of  a  Horizontal  Return-tubular  Boiler. — Fig.  178  shows 
a  modern  form  of  setting  of  a  return-tubular  boiler,  from  a  design 
described  by  S.  F.  Jeter  (Power,  Jan.  3,  1911).  The  following  is 
condensed  from  his  description :  A  good  foundation  should  be  pre- 
pared before  the  arrival  of  the  boiler.  The  manufacturer  of  the 


-R- 


— 1 

SETTING  FOR  FLUSH  FRONT 
FIG.  178. — SETTING'OF  A  HORIZONTAL  RETURN-TUBULAR  BOILER,  FLUSH  FRONT. 

boiler  should  furnish  a  plan  of  the  setting  walls,  and  from  this 
the  dimensions  and  location  of  the  foundation  walls  may  be  obtained. 
If  a  setting  plan  is  not  furnished,  dimensions  may  be  obtained  from  the 
table.  The  depth  of  foundations  and  the  width  of  footings  neces- 
sary depend  upon  the  nature  of  the  soil  at  each  plant.  Where  the 
soil  is  capable  of  supporting  only  light  loads,  a  bed  of  concrete, 
properly  reinforced  and  extending  entirely  over  the  space  occupied 
by  the  setting,  makes  a  satisfactory  foundation.  For  boilers  sup- 
ported on  columns,  the  load  on  the  portions  of  the  foundations 
beneath  the  columns  is  more  concentrated  than  in  the  case  of  lug- 
supported  boilers  resting  directly  on  the  brick-work,  and  it  is  necessary 
that  additional  width  to  the  footings  be  provided  at  the  base  of 
the  columns.  The  foundation  must  be  capable  of  holding  the  boiler 
and  setting  practically  rigid.  A  weak  foundation  will  cause  the 


BOILER  DESIGN  AND  CONSTRUCTION.  453 

walls  to  crack  and  also  may  cause  stresses  on  the  pipe  connections  to 
the  boiler  that  are  apt  to  result  in  a  serious  accident. 

When  the  boiler  arrives  at  is  destination  it  should  be  carefully 
unloaded  and  transported  to  the  site  of  erection.  The  nozzles  are 
most  likely  to  be  damaged  in  handling ;  and  pipes  or  bars  should  never 
be  stuck  in  the  tubes  to  aid  in  moving  the  boiler. 

It  is  best  to  place  a  boiler  in  the  correct  position  with  the  front 
in  place  before  commencing  the  brick-work;  if  the  boiler  is  to  be 
supported  on  lugs  resting  on  the  brick-work  it  should  be  placed  about 
a  half  inch  higher  than  the  desired  final  position,  to  allow  for  lower- 
ing on  the  brick-work  when  the  supports  are  removed.  When  a 
boiler  is  to  be  hung  from  beams  it  can  be  placed  in  the  correct 
position  at  once.  None  of  the  weight  should  be  carried  by  the  boiler 
front,  and  to  insure  against  this,  !/2  to  %  inch  clearance  should  be 
left  between  the  bottom  of  the  shell  and  the  front.  Ample  clearance 
between  the  front  and  shell  is  especially  important  in  the  lug-sup- 
ported type  in  order  to  allow  for  settling. 

The  front  end  of  a  boiler  should  be  placed  about  one  inch  higher 
than  the  rear  to  aid  draining  through  the  blow-off  pipe  when  washing 
out. 

A  mortar  of  lime  and  cement  should  be  used  in  building  boiler 
settings.  Regular  lime  mortar  is  made,  using  three-quarters  of  a 
cubic  yard  of  good,  sharp  sand  to  one  barrel  of  lime,  then  a  mixture 
of  sand  and  cement  is  made,  using  two  barrels  of  sand  to  four  bags 
of  cement  added  to  the  lime  mortar.  This  quantity  of  material 
should  make  enough  mortar  to  lay  about  one  thousand  brick.  If 
all  the  mortar  cannot  be  used  at  once,  the  sand  and  cement  mixture 
should  only  be  added  to  such  portion  of  the  lime  mortar  as  will 
be  required  for  immediate  use,  as  it  is  difficult  to  keep  it  in  proper 
condition  over  night  after  the  cement  has  been  added.  Fire  clay 
is  the  only  bonding  material  that  should  be  used  in  laying  the  fire- 
brick and  for  this  purpose  it  should  be  mixed  with  water  to  about 
the  consistency  of  buttermilk,  so  that  the  bricks  may  be  dipped  in  it 
and  rubbed  together  when  laying  them.  About  two  barrels  of  fire 
clay  are  required  to  lay  one  thousand  brick. 

The  temperatures  attained  in  the  furnaces  of  return-tubular 
boilers  are  generally  moderate,  and  it  does  not  require  a  specially 
high  grade  of  fire-brick  to  withstand  the  heat ;  but  there  is  more  need 
of  mechanical  strength  to  withstand  the  wear  incidental  to  the 
rubbing  of  the  fire  tools  and  breaking  off  clinkers.  On  this  account 
a  medium  grade  of  fire-brick,  costing  about  $22  to  $25  per  thousand, 
will  be  generally  found  most  suitable.  Fire-brick  that  are  made 
especially  with  a  view  to  resisting  the  very  high  temperatures  are 
usually  mechanically  weak  and  soft  and  they  are  also  the  most 
costly.  For  arches  in  Dutch  ovens,  where  there  is  no  danger  of  hitting 
the  brick  with  the  fire  tools,  the  higher  grade  of  brick  generally 
gives  the  best  service.  The  common  brick  used  for  setting  should 
be  well  burned. 


454 


STEAM-BOILER  ECONOMY. 


DIMENSIONS   FOR    BOILER    SETTING. 


Horsepower  on  a 
Basis  of  10  Sq.ft. 
of  Heating  Sur- 
face per  Horse- 
power. 

^Diameter  of  boiler. 
Inches. 

t-Length  of  Tubes, 
W  Feet. 

Number  of  Tubes. 

*o 

T3 
•** 
?j 

I1 

B 

•+j  a?*""1 
eSTJ-r 

£§.3 
23^ 

W^O 

*N 

gfeo} 
J 

La 

*0"-H 

J3  of 

Is 

K 

i 

^3 

*o 

If 

L 

"SJj'awfS 

#:!*! 

ill 

gpq'£«o* 
< 

Number  of  fire- 
ihricks  required  to 
Set  one  Boiler. 

Number  of  Red 
Bricks  required  to 
Set  one  Boiler. 

P 

a 

CO 

-J 

f 

53 

48 

44 

48 

12 

50-3" 
38-3  V 
30-4" 

8'-0" 

26 

48 

42 

16,000 

800 

13,500 

61 

56 

51 

48 

14 

8'-0" 

26 

54 

42 

18,000 

850 

15,000 

72 

63 

51 

54 

14 

60-3" 
44-3  J" 
30-4" 

8'-6" 

28 

54 

48 

23,000 

950 

16.500 

83 

72 

58 

54 

16 

8'-6" 

28 

54 

48 

25,500 

950 

18,000 

99 

88 

86 

60 

1.6 

72-3" 
54-3  £" 
46-4" 

9'-0" 

28 

60 

54 

32,500 

1,100 

18,500 

110 

99 

96 

60 

18 

9'-0" 

28 

66 

54 

35,500 

1,150 

20,000 

130 

118 

108 

66 

16 

98-3" 
74-3i" 
60-4" 

9'-6" 

30 

72 

60 

38,000 

1,350 

20,000 

147 

132 

121 

66 

18 

9'-6" 

30 

78 

60 

41,500 

1,400 

22,000 

163 

149 

131 

72 

16 

124-3" 
96-3*" 
74-4"  f 

10'-9' 

30 

72 

66 

47,500 

1,550 

25,000 

183 

167 

147 

72 

18 

10'-9" 

30 

84 

66 

51,000 

1,600 

27,500 

203 

188 

185 

164 

72 

20 

10'-9" 

30 

90 

66 

56,000 

1,650 

29,500 

175 

161 

78 

16 

144-3" 
114-3J" 
92-4" 

11  '-3" 

34 

72 

72 

50,000 

1,700 

27,000 

211 

197 

181 

78 

18 

11  '-3" 

34 

78 

72 

54,500 

1,750 

29,500 

234 

218 

201 

78 

20 

ll'-3" 

34 

84 

72 

59,000 

1,800 

31,500 

NOTE. — In  using  this  table  for  setting  boilers,  dimensions  F,  J,  M,  and  N  must  conform 
to  the  dimensions  of  the  front  furnished  with  the  boiler  and  dimensions  K  and  L  with  the 
grates  furnished.  On  flush  fronts,  dimensions  Q,  R,  and  S  depend  on  the  dimensions  P,  and 
these  dimensions  must  be  changed  to  conform  to  any  changes  that  may  be  necessary  in  P. 
The  column  giving  the  number  of  common  brick  required  refers  to  the  overhanging-front  style 
of  setting,  and  for  flush  fronts  there  should  be  added  500  to  2500  brick,  depending  upon  the 
size  of  a  boiler. 

ADDITIONAL  DIMENSIONS. 


A 
C 
F 
G 
H 
I 
M 
O 
P* 
Q* 

^| 

S* 


Diameter,  ins  .............................. 

Thickness  of  inside  furnace  walls,  ins  .......... 

Height  of  setting  wall,  ft.  and  ins  ............. 

Thickness  of  bridge  wall,  ins  ................. 

Width  of  top  of  bridge  wall,  ins  .............. 

Top  of  bridge  wall  to  shell,  ins  .............. 

Floor  line  to  bottom  of  shell  at  front,  ins  ...... 

Distance  between  tube  sheet  and  rear  wall,  ins. 

Depth  of  smoke  box,  ins  .............................. 

Thickness  of  front  wall,  ins  .......................... 

Overall  length  of  setting  walls  at  floor  line,  ft.  and  ins.  .  . 
Thickness  of  front  wall  at  floor  line  =0  +4  ins. 


8-0  8-6 


17   1 18 


8-8  9-6  9-10 


17 


72 
21* 


30| 

14 

12 
f>9 
30 
18 
20 


--B+O+P+21  ins. 
=B  +O  +25  ins. 


78 


*  For  flush  fronts  only. 


t  For  overhanging  fronts. 


Keturn-tubular  boilers  are  usually  set  with  an  air-spaced  wall,  as 
illustrated  in  Fig.  179.  The  air  space  reduces  the  temperature  of  the 
outer  wall  surface,  but  introduces  other  losses  that  probably  outweigh 
the  gain  in  economy  due  to  this  feature,  and  it  is  doubtful  if  this 


BOILER  DESIGN  AND  CONSTRUCTION.  455 

form  of  construction  is  better  than  a  solid  wall.  The  chief  advantage 
of  the  air-space  construction  is  that  when  properly  built  it  tends 
to  prevent  the  cracking  of  the  outer  wall  surface  and,,  therefore, 
makes  a  better  looking  setting.  One  important  point  in  the  design 
of  setting  walls,  to  prevent  cracking,  is  the  method  used  to  join  the 
ends  of  the  bridgewall  with  the  side  walls. 

There  are  two  ways  of  preventing  trouble  from  the  expansion 
of  the  bridgewall.  One  is  to  leave  the  ends  of  the  bridgewall  about 
an  inch  away  from  the  side  walls,  packing  the  space  with  asbestos 
or  mineral  wool.  The  elasticity  of  the  packing  allows  for  the 
expansion  of  the  bridgewall  and  it  prevents  the  space  from  becoming 
clogged  with  ash  and  cinders.  The  other  way  is  to  build  a  recess 
about  4  inches  deep  in  the  side  walls  having  the  same  shape 
as  a  vertical  section  of  the  bridgewall  and  build  the  ends  of  the 
bridgewall  into  this  recess,  leaving  1J  inches  of  clearance  at  each 
end  for  expansion. 

The  chief  function  of  a  bridgewall  is  to  limit  the  length  of  the 
grate  surface  by  presenting  a  barrier  beyond  which  the  spreading 
of  the  fuel  is  prevented;  it  also  aids  in  mingling  the  unburned 
gases  and  air,  so  as  to  cause  complete  combustion  before  reach- 
dng  the  tubes.  The  exact  shape  or  height  of  the  bridgewall  does 
not  greatly  affect  the  attainment  of  these  functions.  Where  girth 
seams  are  located  in  the  vicinity  of  the  bridgewall,  the  top  of  the 
wall  should  be  so  shaped  and  of  such  a  distance  below  the  shell 
that  the  products  of  combustion  will  not  impinge  directly  against  the 
seam.  The  top  of  the  bridgewall  should  be  built  straight  across 
and  not  follow  the  contour  of  the  shell  as  is  sometimes  done.  All 
the  bricks  on  top  of  the  bridgewall  should  be  laid  as  headers,  so 
that  they  may  be  better  able  to  resist  being  dislodged  by  the  fire 
tools. 

The  side  walls  of  a  boiler  are  generally  battered  as  shown  in 
Fig.  179;  and  this  is  good  construction;  especially  for  a  lug-supported 
boiler. 

The  combustion  chamber  at  the  rear  of  the  bridgewall  tends 
to  aid  complete  combustion,  especially  if  bituminous  coal  is  used. 
The  rear  edge  of  the  bridgewall  should  be  built  vertical,  and  the 
space  behind  it  down  to  about  the  level  of  the  floor  should  be 
left  open  as  in  Fig.  178,  and  not  filled  up  and  paved  as  in  common 
practice.  The  deep  combustion  chamber  at  the  rear  of  the  bridge- 
wall  tends  to  cause  a  whirl  in  the  air  and  gases  coming  over  it  and 
greatly  aids  in  their  proper  mixture.  It  also  affords  storage  capacity 
for  the  fine  ash  and  cinder  that  is  carried  beyond  the  bridgewall. 
The  practice  of  filling  the  space  behind  the  bridgewall  to  con- 
form to  the  contour  of  the  shell,  as  is  sometimes  done,  cannot  be 
too  strongly  condemned,  for  it  seriously  interferes  with  the  ac- 
cessibility for  inspection  of  the  most  important  surfaces  of  the  boiler, 
and  is  certain  to  prevent  complete  combustion,  if  bituminous  coal  is 
used.  Convenience  in  cleaning  out  the  combustion  chamber  is  obtained 


456  STEAM-BOILER  ECONOMY. 

by  arranging  the  bottom  of  this  chamber  as  illustrated  in  Fig.  178;  so 
that  the  blow-off  pipe  passes  out  below  the  paving,  and  the  cleanout 
door,  which  is  usually  located  in  the  rear  wall,  is  placed  on  a  level  with 
the  paving  so  that  no  obstacle  is  oifered  to  raking  out  the  ashes.  The 
blow-off  pipe  should  be  placed  in  a  brick  trough,  the  bricks  on  top 
being  arranged  so  that  they  may  be  readily  removed  for  inspection. 
This  arrangement  also  admits  of  the  blow-off  pipe  being  placed  above 
the  boiler-room  floor  without  interfering  with  free  access  to  the 
cleanout  doors.  The  vertical  section  of  the  blow-off  pipe  should 
be  protected  from  the  direct  impingement  of  the  flames  by  slipping 
a  pipe  sleeve  over  it;  or  a  form  of  protection  which  is  equally  as 
good,  with  the  blow-off  pipe  accessible  for  inspection,  may  be  made 
by  laying  loose  fire-brick  in  front  of  the  pipe  in  the  form  of  a  V. 

The  amount  of  wall  surface  that  is  required  to  be  lined  with 
fire-brick  is  largely  a  matter  of  opinion;  some  engineers  prefer  to 
line  all  of  the  inner  surfaces  that  are  swept  by  flame  and  heated 
gases;  but,  although  this  makes  a  good  and  lasting  setting,  it  adds 
considerably  to  the  cost.  If  the  front  wall  and  the  side  walls  over  the 
space  indicated  by  the  letters  W,  X,  Y ,  Z ,  Fig.  178,  are  lined,  together 
with  the  bridgewall,  and  the  balance  of  the  setting  is  laid  with 
good,  hard,  burned  red  brick,  a  satisfactory  and  durable  job  will 
result.  Every  fifth  or  sixth  course  of  fire-brick  should  be  a  header 
course  to  properly  bind  the  lining  to  the  main  wall. 

Although  it  has  been  the  general  custom  to  place  binder  bars 
on  side  walls  of  settings,  it  is  a  debatable  question  as  to  whether 
they  are  of  any  real  benefit  or  not,  except  possibly  near  the  front  and 
rear  ends  of  the  setting.  When  a  boiler  is  set  with  a  Dutch  oven, 
there  is  absolute  need  of  binder  bars  or  their  equivalent  to  carry 
the  thrust  of  the  arch,  but  no  such  need  exists  with  the  ordinary 
return-tubular  setting  where  the  boiler  is  hung,  and  probably  not 
where  the  boiler  is  supported  by  lugs  resting  on  the  setting  walls. 

An  important  point  upon  which  depends  the  prevention  of  cracks 
in  the  walls  of  the  setting,  is  the  proper  provision  for  expansion  of 
the  boiler.  In  supporting  the  boiler  on  lugs  it  is  generally  attempted 
to  secure  this  feature,  in  part,  by  providing  rollers  under  one  pair 
of  lugs  (usually  the  rear  lugs).  These  rollers  prevent  a  lengthwise 
thrust  on  the  walls  due  to  the  expansion  of  the  shell;  but  it  is 
doubtful  if  they  are  of  much  real  value  because  they  do  not  provide 
for  any  movement  across  the  setting.  For  instance,  in  a  72-in.  by 
16-ft.  boiler 'the  longitudinal  distance  between  the  centers  of  the  lugs 
is  about  8  ft.,  while  the  distance  between  centers  across  the  boiler 
is  about  7  ft.;  hence,  the  movement  across  the  setting  that  should 
be  cared  for  is  about  as  great  as  it  is  lengthwise,  and  the  rollers 
do  not  aid  the  movement  in  this  direction.  The  method  of  making 
allowance  for  expansion  between  the  shell  and  setting  is  shown 
in  Fig.  180,  where  a  1-inch  space  is  left  between  them  and  the  space 
filled  with  plastic  asbestos  or  asbestos  rope.  The  brick-work  should 
not  be  allowed  to  touch  the  boiler  at  any  point,  and  special  care  must 


BOILER  DESIGN  AND  CONSTRUCTION. 


457 


be   taken  to   keep   it   free   from   the   rear   supporting  lugs,  pockets 
usually   being  left  in  the   walls   for   this   purpose.      Another  point 


Asbestos 


1  Space  between 
Brickwork  and  Shell 
filled  with  Asbestos 


oooooooooooo 
oooooooooooo 
oooooooooooo 
oooooooooooo 
oooooooooooo 
oooooooooo 

000    „  000 


ISpace  filled  with  Asbestos 


FIG.  179. — CROSS-SECTION  OF  SET-     FIG.  180. — SHOWING  CLEARANCE  AT  ENDS 
TING.  OF  BRIDGEWALL  AND  AROUND  SHELL. 

where  clearance  is  of  vital  importance  is  around  the  pipe  connections 
to  the  water  column  and  the  blow-off  pipe,  for,  unless  proper  free- 


U  Bolt  to  Fasten  Arch  Bars 


to  Angle  Iron 

— 1 1 r 


OOOOOOOOOOOO 

ooooooo  ooooooo 

ooooooo  ooooooo 

ooooooo  ooooooo 

oooooo  oooooo 

oooooo  oooooo 

ooooo  ooooo 


FIG.  181. — BEST  FORM  OF  COVER- 
ING FOR  REAR  CONNECTION. 


FIG.  182. — CROSS  ARCH  FOR  COVERING 
BACK  CONNECTION. 


dom  is  allowed  at  these  points,  there  is  danger  of  the  pipes  being 
broken  off. 

The  back  connection  covering  is  one  of  the  most  difficult  points 
about  a  boiler  setting  to  keep  tight.    A  good  plan  is  shown  in  Pig.  181. 


458  STEAM-BOILER  ECONOMY. 

The  usual  arrangement  of  this  form  of  covering  is  to  have  an  angle 
iron  bolted  to  the  boiler  head,  with  the  ends  of  the  arch  bars  resting 
on  it,  but  the  angle  is  apt  to  burn  off  in  a  short  time.  It  is  better 
to  fasten  the  tops  of  the  arch  bars  to  the  angle  iron  by  U-bolts,  as 
shown  in  the  cut.  It  is  not  necessary  to  bolt  the  angle  iron  to  the 
boiler  head.  With  this  form  of  covering  the  arches  follow  the 
movement  of  the  boiler  head;  and  by  covering  the  whole  surface 
with  plastic  asbestos  about  2|  in.  thick,  a  tight  job  is  insured. 
One  of  the  desirable  features  of  this  form  of  covering  for  the  back 
connection  is  that  it  presents  a  straight  line  across  the  head  above 
the  tubes,  affording  ample  protection  against  overheating  to  the 
portion  of  the  head  above  the  water  line,  without  interfering  with  the 
free  passage  of  heated  gases  to  any  of  the  tubes. 

Another  method  of  closing  in  the  back  connection  that  is  commonly 
used  throughout  the  East,  is  illustrated  in  Fig.  182.  In  setting  this 
type  of  arch,  care  must  be  taken  that  the  head  above  the  water  line 
is  not  exposed;  and  it  is  sometimes  necessary  to  partially  block  off 
one  or  two  of  the  outside  tubes  to  accomplish  this.  In  the  arrange- 
ment of  all  types  of  covering  for  the  back  connection*  the  fusible  plug 
must  be  left  uncovered  so  that  it  is  freely  exposed  to  the  products 
of  combustion. 

The  best  covering  for  the  exposed  surface  on  top  of  a  boiler, 
and  the  one  that  will  reduce  the  radiation  losses  to  a  minimum,  is 
85%  megnesia  from  2  to  3  in.  thick,  the  outer  layer  being  made 
with  a  hard  finishing  cement.  The  usual  covering  consists  of  a 
layer  of  bricks  laid  on  edge;  but  such  covering  only  has  cheapness 
and  durability  to  recommend  it,  as  it  is  practically  worthless  as  an 
insulator.  The  water  column  should  be  placed  so  that  the  lowest 
gage  cock,  is  at  least  3  in.  above  the  tops  of  the  tubes,  and  the 
lowest  point  of  vision  in  the  gage  glass  at  least  %  in.  above  the 
tops  of  the  tubes. 

Fire-brick  Furnace  Arches.  (A.  E.  Dixon,  Power,  Eeb.  20,  1912). 
— Eire-clay  mortar  must  be  very  thinly  mixed.  Within  limits,  the 
thinner  the  better.  The  brick  should  be  dipped  in  the  mortar  in  such  a 
way  that  the  surface  to  be  exposed  to  the  flame  or  heat  and  two- 
thirds  of  the  surface  in  the  wall  do  not  receive  any  mortar.  The 
back  of  the  brick  and  the  rear  third  of  the  wall  surface  only  are/' 
covered  with  the  mortar.  The  bricks  must  be  hammered  up  tight  to 
each  other  and  the  seams  on  the  top  of  the  arch  should  be  very 
thin;  the  fire-face  of  all  seams  must  be  slightly  open,  in  order  to 
permit  the  fire-face  of  the  brick  to  expand  slightly  when  heated. 

Fire-clay  used  for  mortar  should  be  the  same  clay  as  used  in  the 
brick.  The  best  mortar  is  made  from  a  mixture  ranging  from  20  to 
30%  of  raw  clay  and  70  to  80%  from  old  fire-brick  ground  for  this 
purpose.  The  two  kinds  of  clay  are  thoroughly  mixed  before  they 
are  wet,  then  mixed  with  water  in  a  tank  or  tub  and  allowed  to 
stand  at  least  48  hours  before  using. 

Fire-brick   arches   generally   have   a   rise   of   from   1^   to   2J   in. 


BOILER  DESIGN  AND  CONSTRUCTION.  459 

per  foot  of  span.  The  flatter  the  arch,  the  greater  the  thrust  upon 
the  skewbacks  and  buckstays  and  the  greater  the  pressure  on  the 
bricks  near  the  spring  of  the  arch.  As  fire-brick  are  not  adapted  to  carry 
great  weights,  particularly  when  exposed  to  high  temperatures,  an 
arch  should  be  given  as  great  a  rise  as  possible,  particularly  if  of  any 
great  length  of  span.  Spans  under  4  or  5  ft.,  however,  can  be 
made  very  flat.  The  thrust  of  an  arch  under  a  uniform  load  may 
be  computed  by  the  formula  : 


in  which  T  =  thrust  in  Ibs.  per  sq.  ft.  of  cross-section  per  foot  of  length 
of  arch;  p  =  load  on  arch,  Ib.  per  sq.  f  t.  ;  d  =  span  of  arch  in  feet, 
skewback  to  skewback;  h  =  rise  of  arch  in  inches. 

In  the  case  of  fire-brick  arches,  the  weight  per  cubic  foot  can  be 
assumed  as  130  Ibs.  ;  this  will  be  the  load  per  square  foot  if  the  arch 
is  12  in.  thick.  The  thrust  per  lineal  foot  T  and  the  spacing  of  the 
buckstays  should  be  such  that  the  tie-rods  are  not  stressed  higher  than 
9000  to  10,000  Ibs.  per  sq.  in.  Skewback  supports  are  desirable  to 
carry  the  arch-thrust  between  the  buckstays.  Heavy  angle  or  chan- 
nel irons  are  frequently  employed.  These  are  subjected  to  bending 
stresses  and  should  be  worked  at  very  low  fibre  stresses  in  order  to 
avoid  the  racking  of  the  brick-work  which  would  be  occasioned  if 
they  deflected  or  sprung  very  much  under  the  loads  placed  upon  them. 

To  illustrate  the  effect  of  the  rise  of  an  arch  upon  the  thrust, 
the  thrust  of  an  arch  12  in.  thick  with  a  span  of  12  ft.  6  in.,  has 
been  computed  for  four  different  rises.  This  span  is  approximately  the 
width  of  the  firebox  under  a  600  H.P.  water-tube  boiler. 

Rise  per  Foot,  Thrust,  Pounds  per 

Inches.;  Linear  Foot. 

1.0  2420 

1.5  1630 

2.0  1220 

2.5  975 

The  total  rise  for  these  four  cases  would  be  12.5,  18.75,  25.0  and 
31.25  in.,  respectively,  and  while  the  first  is  so  flat  that  it  gives 
a  pressure  on  the  skewbacks  of  16.8  Ibs.  (2420  -T-  144)  per  square  inch, 
it  is  not  unreasonably  high.  The  other  rises  would  be  too  high  for 
a  coking  arch  under  the  tubes  of  a  water-tube  boiler,  but  they  would 
be  all  right  in  a  Dutch  oven.  It  is  not  desirable  to  run  the  pressure 
on  fire-brick  much  over  25  Ibs.  per  square  inch  or  3600  Ibs.  per 
square  foot. 

Hollow  Walls  Not  an  Advantage.  —  Tests  reported  in  Bulletin  8 
of  the  U.  S.  Bureau  of  Mines,  1911,  indicate  that  in  furnace  con- 
struction a  solid  wall  is  a  better  heat  insulator  than  a  wall  of  the 
same  total  thickness  containing  an  air  space.  This  is  particularly 
true.  if  the  air  space  is  close  to  the  furnace  side  of  the  wall,  and  if 


460  STEAM-BOILER  ECONOMY. 

the  furnace  is  operated  at  high  temperatures.  If  it  is  desirable  in 
furnace  construction  to  build  the  walls  in  two  parts,  so  as  to  prevent 
cracks  being  formed  by  the  expansion  of  the  brick  work  on  the  furnace 
side  of  the  walls,  it  is  preferable  to  fill  the  space  between  the  two 
walls  with  some  "solid"  (not  jirm,  but  loose)  insulating  material. 
Any  such  materials  as  ash,  crushed  brick,  or  sand  offer  higher  resistance 
to  heat  flow  through  the  walls  than  an  air  space.  Such  loose  material 
also  reduces  air  leakage.  A  1-in.  air  space  filled  with  asbestos  gave 
more  resistance  to  the  flow  of  heat  than  a  2-in.  air  space  with  air  only. 
Fire-brick  for  Furnaces.  (W.  N.  Best,  Proc.  N".  Y.  Railroad 
Club,  1912.) — With  liquid  fuel  we  can  attain  and  maintain  a  tem- 
perature far  in  excess  of  that  which  any  ordinary  refractory  material 
can  withstand.  The  quality  of  the  various  fire-bricks  on  the  market 
varies  greatly.  If  furnaces  are  not  operated  continuously,  that  is, 
day  and  night,  it  is  essential  to  carefully  select  fire-brick  having  no 
perceptible  expansion  or  contraction,  and  for  welding  purposes  the 
furnaces  should  be  constructed  of  fire-brick  capable  of  withstanding 
3000°  F.,  without  dripping  or  melting  away.  The  analysis  of  such 
brick  is  as  follows :  Silica,  56.15 ;  alumina,  33.29 ;  peroxide  iron, 
0.59;  lime,  0.17;  magnesia,  0.121;  water  and  inorganic  matter,  9.68; 
total,  100%. 


CHAPTER  XIV. 


BOILER  ATTACHMENTS   AND  BOILER-ROOM  APPLIANCES. 

Mud  Drums  .—When  muddy  water,  such  as  that  of  many  Western 
rivers,  is  used,  it  is  often  customary  to  provide  a  large  mud  drum 
beneath  the  boiler  as  shown  in  Fig.  183.  Such  drums  are  often  a 
source  of  danger  on  account  of  ex- 
ternal corrosion,  which  is  apt  to 
take  place  whenever  they  are  in  a 
damp  atmosphere  at  a  temperature 
below  the  boiling-point  of  water. 
The  mud  drum  of  the  ordinary 
form  of  Babcock  &  Wilcox  boiler 
is  shown  below  the  bank  of  tubes 
in  Fig.  127,  page  361.  It  is  made 
of  small  diameter,  not  over  18  in., 
and  for  pressures  not  over  150  Ibs. 
is  made  of  cast  iron,  which  is  FlG-  ISS.-OLD-STYLE  MUD  DRUM 
less  liable  to  corrosion  than  wrought  iron  or  steel.  The  mud  drum 
in  modern  practice  is  often  reduced  to  a  mere  pipe,  or  is  dispensed 
with  entirely. 


ow-off 


shell  of  Boiler 

FIG.  184. — INTERNAL  MUD  DRUM. 

The  mud  drum  is  sometimes  put  inside  of  the  water  and  steam 
drum  of  a  water-tube  boiler,  as  shown  in  Fig.  184,  which  represents 
the  mud  drum  of  the  Keeler  boiler. 

The  feed  water  is  introduced  through  the  front  head  into  a 
submerged  sheet-steel  mud  drum.  It  is  heated  in  its  passage  through 
the  surrounding  water,  and  before  it  leaves  this  drum  at  the  front  end 
is  of  practically  the  same  temperature  as  the  rest  of  the  water  in  the 
boiler.  This  high  temperature  causes  the  precipitation  of  most  of 

461 


462 


STEAM-BOILER  ECONOMY. 


the  impurities  in  the  lower  end  of  the  drum  to  be  blown  out  through 
the  outlet  in  the  rear  head  provided  for  that  purpose.  The  internal 
mud  drum  also  serves  to  prevent  the  feed  from  coming  in  contact 
with  hot  plates,  with  consequent  contraction  and  leakage  at  the  seams. 
Impurities  carried  into  the  general  circulation  are  discharged  through 
the  main  blow-off  openings  in  the  bottom  of  the  rear  header. 

Blow-off  Pipe. — Two  methods  of  arranging  the  blow-off  pipe 
of  horizontal  tubular  boilers  are  shown  in  Figs.  185  and  186.  In 
the  first  the  descending  pipe  is  protected  from  the  heat  of  the  gases 
by  a  sleeve  of  fire-brick,  and  the  tee  and  the  horizontal  pipe  are 
protected  by  ashes.  In  the  second  the  blow-off  pipe  is  connected 


FIG.  185. — BLOW-OFF  WITH 
CIRCULATING  PIPE. 


FIG.  186. — BLOW-OFF  PROTECTED 
BY  TILE. 


to  a  circulating  pipe  which  enters  the  rear  head  of  the  boiler.     Some- 
times the  descending  pipe  is  protected  by  a  brick  pier. 

Blow-off   Valve.  —  The    common    forms    of   globe   or   gate    valves 
are  scarcely  suitable  for  blow-off  valves'  of  boilers,  as  the  seats  and 

valve  faces  are  apt  to  be  abraded  and 
scored  by  the  particles  of  scale  discharged 
from  the  boiler.  Special  valves  with  re- 
newable discs  and  seats  are  commonly 
furnished  by  the  leading  boiler  makers. 
Blow-off  Tank.  —  In  buildings  in  cities, 
where  it  is  not  permitted  to  blow  down 
a  boiler  under  steam  pressure,  discharg- 
ing hot  water  into  the  sewer,  it  is  cus- 
tomary to  provide  a  tank,  Fig.  187, 
into  which  the  water  is  discharged  and 
allowed  to  cool  before  being  run  to  the 


FIG.  187.  —  BLOW-OFF  TANK, 

Steam  Dome.  —  A  braced  steam  dome,  such  as  was  fifty  years  ago 
in  common  use  with  return-tubular  boilers,  but  is  now  obsolete,  is 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  REQUIREMENTS.    463 

shown  in  Fig.  188.  The  Massachusetts  Board  of  Boiler  Rules  says 
(1910)  :  "The  Board  does  not  recommend  a  steam  dome  on  a  boiler, 
but  does  recommend  the  use  of  a  deflecting  plate  or  a  dry  pipe." 


FIG.  188. — BRACING  OF  A  STEAM 
DOME. 


FIG.  189.— DRY  PIPE. 


Dry  Pipe. — One  form  of  dry  pipe  is  shown  in  Fig.  189.  It  is  a 
long  pipe  capped  at  the  end,  suspended  near  the  shell  in  the  upper 
part  of  the  steam  space  of  a  horizontal  boiler,  with  its  upper  portion 
drilled  with  a  great  number  of  small  holes  whose  aggregate  area  is 
about  double  the  cross-sectional  area  of  the  pipe.  With  such  a  pipe  the 
amount  of  water  discharged  with  the  steam  from  the  boiler  rarely 
exceeds  0.5%  unless  the  water  level  is  carried  too  high  or  the  water 
is  of  such  a  character  as  to  cause  foaming. 

Connecting  Steam  Pipes  to  Boilers. — Fig.  190  (from  The  Locomo- 
tive, 1890)  shows  an  incorrect  method  of  attaching  pipes  connecting 
a  pair  of  boilers  to  an  overhead  steam  main.  The  cast-iron  pipe  C 


FIG.  190. — INCORRECT  PIPING. 


FIG.  191. — IMPROVED  PIPING. 


formed  a  rigid  connection  between  the  two  boilers,  allowing  no  pro- 
vision for  expansion  and  contraction.  After  the  boilers  had  been  a 
short  time  in  service  the  tee  at  A  cracked  as  shown;  it  was  replaced 
and  soon  afterward  the  pipe  C  cracked  at  B.  In  another  case,  observed 
by  the  author,  in  which  two  water-tube  boilers  were  connected  in  a 


464  STEAM-BOILER  ECONOMY. 

similar  manner,  but  with  a  wrought-iron  pipe,  the  expansion  and  con- 
traction brought  a  strain  on  the  boilers  themselves,  causing  one  of 
them  to  leak  seriously  at  a  riveted  seam. 

Fig.  191  shows  a  common  method  of  connecting  a  boiler  to  a  steam 
main.  The  vertical  pipe  AB  is  connected  by  a  long  horizontal  pipe 
to  the  main  Df  which  gives  the  piping  system  the  required  flexibility. 


FIG.  192. — ECCENTRIC  FITTINGS  FOR  BRANCHES. 

In  modern  plants  with  high  pressures  the  elbow  D  is  usually  replaced 
by  a  long  bend  of  wrought-iron  or  steel  pipe  ,and  cast-iron  flanges 
and  elbows  are  generally  avoided. 

Eccentric  Fittings. — When  several  boilers  in  a  battery  discharge 
into  a  horizontal  steam  main  or  drum  from  which  pipes  lead  to  the 
engine  it  is  essential  that  connections  be  so  made  that  at  no  time  is 
it  possible  for  any  water  to  collect  in  the  lower  part  of  the  drum.  The 
best  way  to  insure  this  is  to  have  the  connections  to  the  drum  made  of 
eccentric  fittings,  so  that  the  bottom  of  the  inside  of  the  fitting,  or 


FIG.  193. — ECCENTRIC  FITTINGS  FOR  PIPE  LINES. 

nozzle,  is  at  the  level  of  the  bottom  of  the  drum.    Three  forms  of  such 
nozzles  are  shown  herewith,  Fig.  192. 

Fig.  193  shows  eccentric  fittings  for  a  long  line  of  steam  pipe,  when 
the  size  of  the  main  is  to  be  reduced,  which  allow  water  of  conden- 
sation to  flow  freely  onward. —  (The  Locomotive,  1900.) 

Fire-Doors. — The  ordinary  form  of  fire-door  is  shown  in  Fig.  194. 
The  admission  of  air  through  the  adjustable  opening  in  front  and 
thence  through  the  perforated  plates  tends  to  keep  the  door  from 
overheating  and  warping.  Fig.  195  shows  a  form  of  balanced  door. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  REQUIREMENTS.    465 

The  door  is  suspended  by .  horizontal  pivots  at  its  upper  edge,  and  a 
heavy  counterbalance  weight  is    mounted  above  it  in  such  a  position 


0<°>0  00000  0<°>0 
00000000000 

ooooooooooo 
ooooooooooo 
ooooooooo  oo 

000  00000000 

o<S>o  oooooo<S>o 


FIG.  194. — DETAILS  OF  FIRE-DOORS. 

that  if  the  door  when  closed  is  given  a  slight  push  it  will  open 
inwards  and  will  close  again  when  a  push  is  given  the  counterweight. 
Doors  of  this  type  are  frequently  used  on 
ocean  steamers. 

Fire-door  Openings. — With  externally- 
fired  boilers  the  fire-door  opening  is  part  of 
the  brick  setting  of  the  furnace.  The  open- 
ing is  arched  over  with  arch  fire-brick  or 
with  a  special  tile  of  the  proper  shape  and 
material.  The  door  opening  is  from  12x16 
in.  to  16x20  in.  For  wide  grates  two  small 
doors  are  commonly  preferred  to  one  large 


FIG.  195.— BALANCED 
FIRE-DOOR. 


one,  and  three  or  more  doors  if  the  grate  surface  is  over  8  ft.  in 
width.  With  internally-fired  boilers  the  fire-door  opening  is  part  of 
the  boiler  structure.  Fig.  196  shows  different  methods  of  making 
such  openings  in  vertical  tubular  or  other  internally-fired  boilers. 


•  P 


-tr- ' 


FIG.  196. — FIRE-DOOR  OPENINGS  FOR  INTERNALLY-FIRED  BOILERS. 

Red-hot  Fire-doors. — A  complaint  was  made  that  the  fire-doors  of 
a  certain  water-tube  boiler  were  frequently  red  hot  and  it  was  feared 


466 


STEAM-BOILER  ECONOMY. 


they  would  soon  be  burned  out.  The  furnace  was  roofed  over  by  an 
inclined  brick  arch  which  sometimes  became  intensely  hot  and  radiated 
heat  onto  the  fire-doors  and  into  the  fireman's  face  whenever  he  opened 
a  door.  The  coal  was  Pittsburgh  bituminous.  It  was  discovered 
that  the  doors  never  got  visibly  red  unless  the  fireman  waited  at 
least  15  minutes  after  firing,  and  that  when  they  did  get  hot  the 
firing  of  a  single  shovelful  of  coal  just  beyond  the  dead  plate  be- 
tween the  door  and  the  grate  bars  cooled  the  door  so  that  it  would  not 
again  become  red  hot  for  at  least  ten  minutes.  When  the  fireman 
changed  his  method  of  firing,  and  fired  in  smaller  quantities  at  me/re 
frequent  intervals,  there  was  no  more  complaint  of  hot  fire-doors. 

Nozzles  for  Attaching  Pipes  to  Boilers. — For  pressures  not  ex- 
ceeding 150  Ibs.  it  is  customary  to  make  nozzles  of  cast  iron,  but  for 

higher  pressures  forged  steel  is  recom- 
mended. Fig.  197  shows  a  forged  steel 
nozzle  for  a  steam  pipe  connection  con- 
taining an  internal  pipe  which  connects 
with  a  dry-pipe  inside  of  the  boiler. 
Brackets  and  Hangers  for  Support- 

F»o.  197.-FOEGED  STEEL  NOZZLE  ***  Boilers—Horizontal  tubular  boilers 
WITH  DRY-PIPE  CONNECTION,     of  moderate  sizes  are  usually  supported 

on  the  brick  walls  of  the   setting  by 

means  of  cast-iron  brackets  riveted  to  the  shell,  Fig.  198,  two  such 
brackets  being  used  on  each  side,  and  the  rear  ones  often  resting  on 


FIG.  198. — SIDE  BRACKETS. 


FIG.  199. — METHODS  OF  SUPPORTING  BOILERS  FROM  ABOVE. 

rollers  carried  by  a  plate  on  the  top  of  the  wall,  so  as  to  allow  of 
expansion   and   contraction.     Large   high-pressure   boilers   and   also 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  REQUIREMENTS.    467 

water-tube  boilers  are  generally  carried  by  hangers  from  overhead 
supports  which  are  entirely  free  from  the  brickwork  setting.  Fig. 
199  shows  different  forms  of  hangers.  The  brackets  for  these  hangers 
are  made  of  cast  or  forged  steel. 

Feeding  Boilers. — The  old  practice  of  feeding  boilers  through 
the  mud  drum  is  now  generally  condemned.  It  tends  to  cause 
corrosion  and  pitting  of  the  metal  near  the  inlet  orifice,  and  it  stirs 
up  the  mud  in  the  drum,  carrying  it  up  into  the  boiler  where  it  may 
cause  the  formation  of  scale.  Feeding  through  the  front  head  of  a 
tubular  boiler  below  all  the  tubes  is  also  condemned  on  account  of 
the  frequent  changes  of  temperature  caused  thereby.  The  following 
method  of  feeding  return-tubular  boilers  is  recommended  by  the  Hart- 
ford Steam  Boiler  Inspection  and  Insurance  Co.  The  feed-pipe  enters 
the  boiler  through  the  front  head  just  above  the  top  row  of  tubes, 
and  about  three  inches  from  the  shell.  It  then  extends  back  to  within 
a  foot  of  the  back  head  and  crosses  over  to  the  other  side  of  the 
boiler.  It  then  passes  down  between  the  tubes  and  the  boiler  shell 
and  discharges  below  the  lowest  row  of  tubes  towards  the  axis  of  the 
boiler.  The  vertical  pipe  in  front  of  the  boiler  contains  a  stop  valve, 
a  check  valve  and  a  union.  The  advantage  of  this  method  lies  in  the 
fact  that  before  the  feed-water  discharges  itself  it  has  become  as  hot 
as  the  water  into  which  it  is  discharged,  and  consequently  there  is 
no  chilling  effect  produced,  and  no  unequal  expansion  and  contraction 
of  the  boiler.  Brass  pipe,  inside  of  the  boiler,  is  preferable  to  iron 
pipe,  because  it  will  not  choke  with  scale  as  quickly  as  iron  pipe. 
The  piping  can  be  so  connected  together  that  only  the  portion  running 
across  the  boiler  need  be  taken  out  for  cleaning,  while  the  long  section 
may  be  cleaned  in  place  by  running  an  iron  rod  through  it. 

The  feed  pipe  of  water-tube  boilers  with  horizontal  drums  is 
usually  made  to  enter  the  front  head  and  to  travel  to  a  point  near  the 
rear  head  where  the  water  is  discharged  into  the  rapidly  flowing 
rearward  current  in  the  boiler.  This  method  is  generally  satisfactory 
except  when  the  water  contains  a  great  deal  of  carbonate  of  lime 
and  magnesia,  which  is  apt  to  be  deposited  as  scale  in  the  downcome 
pipes  at  the  rear  of  the  boiler.  In  such  case  it  is  better  to  provide 
the  boiler  with  an  internal  mud  drum  and  feed  into  it.  (See  Fig.  184.) 

Attachments  to  Boilers.  (Massachusetts  Boiler  Rules.)  •-  Safety 
Valves. — Each  safety  valve  shall  have  full-sized  direct  connection  to 
the  boiler.  No  valve  shall  be  placed  between  the  safety  valve  and 
the  boiler,  nor  on  the  escape  pipe  between  the  safety  valve  and  the 


468  STEAM-BOILER  ECONOMY. 

atmosphere.  Safety  valves  shall  not  exceed  5  in.  diameter,  and  shall 
be  of  the  direct  spring-loaded  type,  with  seat  and  bearing  surface 
of  the  disc  at  an  angle  of  about  45°  to  the  center  line  of  the  spindle, 
with  a  lifting  device  so  that  the  disc  can  be  lifted  from  its  seat  not 
less  than  %  the  diameter  of  the  valve  when  the  pressure  on  the 
boiler  is  75%  of  that  at  which  the  safety  valve  is  set  to  blow. 

Steam  Gage. — Each  boiler  shall  have  a  steam  gage  connected  to 
the  steam  space  of  the  boiler  by  a  siphon,  or  equivalent  device,  in 
such  manner  that  the  gage  cannot  be  shut  off  from  the  boiler  except 
by  a  cock  with  T  or  lever  handle,  which  shall  be  placed  on  the  pipe 
near  the  steam  gage. 

Steam  Gage  Dial. — The  dial  of  the  steam  gage  shall  be  graduated 
to  not  less  than  Ij  times  the  maximum  pressure  allowed  on  the  boiler. 

Attaching  Test  Gage. — Each  boiler  shall  be  provided  with  a  %- 
in.  pipe  for  attaching  inspector's  test  gage  when  the  boiler  is  in  ser- 
vice, so  that  the  accuracy  of  the  boiler  steam  gage  can  be  ascertained. 

Water  Glass. — Each  boiler  shall  have  at  least  one  water  glass, 
the  lowest  visible  part  of  which  shall  be  above  the  fusible  plug  and 
lowest  safe  water  line. 

Gage  Codes. — Each  boiler  shall  have  three  or  more  gage  cocks, 
located  within  the  range  of  the  visible  length  of  water  glass,  when  the 
maximum  pressure  allowed  exceeds  25  Ibs.  per  sq.  in.,  except  when 
such  boiler  has  two  water  glasses,  located  not  less  than  3  ft.  apart,  on 
the  same  horizontal  line. 

Feed  Pipe. — Each  boiler  shall  have  a  feed  pipe  fitted  with  a  check 
valve,  and  also  a  stop  valve  or  stop  cock  between  the  check  valve  and 
the  boiler,  the  feed  water  to  discharge  below  the  lowest  safe  water 
line.  Means  must  be  provided  for  feeding  a  boiler  with  water  against 
the  maximum  pressure  allowed. 

Stop  Valve. — Each  steam  outlet  from  a  boiler  (except  safety  valve 
connections)  shall  be  fitted  with  a  stop  valve. 

When  a  stop  valve  is  so  located  that  water  can  accumulate,  ample 
drains  shall  be  provided. 

Damper  Regulator. — When  a  damper  regulator  is  used,  the  boiler 
pressure  pipe  shall  be  fitted  with  a  valve  or  cock,  and  shall  be  con- 
nected to  the  steam  space  of  the  boiler. 

Fusible  Plugs  to  be  filled  with  pure  tin;  plugs  to  project  through 
the  sheet  not  less  than  1  in.  In  horizontal  return  boilers,  the  plugs 
are  to  be  located  in  the  rear  head,  not  less  than  2  inches  above  the 
upper  row  of  tubes;  in  water-tube  boilers  with  horizontal  drums, 
Babcock  &  Wilcox  type,  not  less  than  6  inches  above  the  bottom  of 
the  drum,  over  the  first  pass  of  the  products  of  combustion ;  in  new 
designs,  at  the  lowest  permissible  water  level,  in  the  direct  path  of 
the  products  of  combustion,  as  near  the  primary  combustion  chamber 
as  possible. 

The  Board  of  Boiler  Rules  Recommends:  The  installation  of  more 
than  one  safety  valve  on  a  boiler  permitted  to  carry  over  25  Ibs. 
pressure  per  sq.  in. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.   469 


Elliptical  handholes  of  the  following  sizes :  2J  x  3J  in.;  2fx3f 
in.  ;  3x4^  in. ;  3 \  x  5  in. ;  4  x  6  in. 

Discontinuing  from  service,  and  not  repairing  a  boiler  on  which 
a  longitudinal  lap  crack  is  discovered. 

The  Board  Does  not  Recommend:  The  use  of  cast-iron  or  copper 
steam  pipe. 

Attaching  diagonal  stays  to  shell  plates  directly  over  the  fire. 

Safety- Valves. — The  Massachusetts  rule  for  area  of  safety-valves  is 

W  X  70 
A  = — X  11,  in  which  A  '=  area  in  square  inches  per  square 

foot  of  grate  surface,  W  =  pounds  of  water  evaporated  per  second  per 


FIG.  200. — LEVER  SAFETY-VALVE. 


• 

s 

1 

_ 

L 

FIG.  201. — BEVEL-SEAT 
SAFETY-VALVE. 


FIG.  202.— CROSBY  FLAT- 
SEAT  SAFETY-VALVE. 


square  foot  of  grate  surface  =  P  =  absolute  pressure  of  the  steam  in 
pounds  per  square  inch.  The  words  "per  square  foot  of  grate  surface" 
seem  to  be  a  concession  to  an  old  custom  of  proportioning  the  area  of  a 
safety-valve  to  the  grate  surface,  but  in  this  formula  they  are  mere 
surplusage,  for  the  formula  is  -equivalent  to  A  =  770  W/P,  in  which 
A  is  square  inches  of  valve  area  and  W  pounds  of  water  evaporated 
per  second.  It  is  also  equivalent  to  Napier's  formula  for  flow  of 
steam  through  an  orifice,  W  =  AP/7Q,  assuming  the  area  of  opening 


470  STEAM-BOILER  ECONOMY. 

of  the  valve  =  1/11  of  the  disc  area.    This  rule  will  probably  soon  be 
obsolete. 

Fig.  200  shows  the  old  style  of  safety-valve,  in  which  an  ordinary 
bevel-seated  valve  is  held  to  its  seat  by  a  weighted  lever.  Its  chief 
defect  was  that  it  opened  only  slightly  when  the  steam  pressure 
reached  the  limit  for  which  the  weight  on  the  lever  was  set,  and 
would  not  lift  higher  as  the  pressure  increased.  For  high-pressure 
boilers  the  "pop"  safety-valve  is  in  almost  universal  use.  The  valve 
is  held  down  by  a  compressed  coiled  spring,  and  is  so  shaped  that 
after  it  opens  the  steam  presses  upon  a  larger  area  than  that  which 
is  exposed  to  pressure  when  the  valve  is  shut.  This  causes  the  valve 
to  lift  higher  than  the  old-style  valve,  and  retards  its  closing  until  the 
steam  pressure  has  been  reduced  io  a  point  slightly  below  that  at  which 
the  valve  opens.  Fig.  201  shows  such  a  valve,  called  a  single  or 
bevel-seated  valve,  and  Fig.  202,  another,  called  a  double-seated 
annular  valve,  in  which  the  additional  area,  upon  which  the  steam 
presses  when  the  valve  is  opened,  is  located  at  the  center  of  the 
valve  disc.  Both  the  inner  and  outer  seats  of  this  valve  are  flat. 
Fig.  202  also  shows  the  coiled  spring,  which  is  adjusted  to  the  allowed 
pressure  by  the  screw  and  lock-nut  shown  above.  The  casing  of  the 
valve  may  be  provided  with  a  muffling  device,  for  lessening  the  noise 
when  steam  is  blowing  off.  The  rounded  edge  shown  at  A  increases 
the  discharge  about  12  per  cent  above  that  of  a  sharp-edged  outlet. 

The  boiler  rules  of  the  State  of  Massachusetts  provide : 

"No  valve  of  any  description  shall  be  placed  between  the  safety 
valve  and  the  boiler,  or  on  the  escape  pipe  between  the  safety-valve 
and  the  atmosphere/' 

.     Discharging  Capacity  of  Safety-Valves. — The  table  on  page  471 
shows  the  discharge  of  Crosby  safety-valves  for  the  various  lifts  given : 

Safety-valve  Rules  of  the  A,  S.  M.  E.  Boiler  Code.— In  1914 
the  Committee  had  several  conferences  with  the  principal  safety-valve 
manufacturers  of  the  country  and  an  agreement  was  finally  reached 
on  the  rules  given  in  condensed  form  below.  The  discharging  capacity 
of  a  valve  is  based  on  Napier's  rule  with  a  coefficient  of  discharge  of 
0.96,  the  formula  being  W  =  3600  X  3.1416  XDL  X  0.96  X  0.707 
X^P/^0,  or  W  =  109.66  DLP  pounds  per  hour  for  a  45°  bevel  seat 
valve.  For  flat  seat  valves  the  factor  0.707  is  omitted  and  the  formula 
becomes  W  =  155.11  DLP  pounds  per  hour.  The  table  on  page  472  is 
calculated  from  the  first  formula.  (D  =  diam.  L  —  lift,  both  in  inches, 
P  =  absolute  pressure,  Ibs.  per  sq.  in.,  G  =  gage  pressure  +  14.7.) 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.  471 


ASSUMED   LIFTS,    VARYING   WITH   VALVE    SIZE    AND    PRESSURE. 


Press 

ures  (Lb 

3.  per  Sq 

In.) 

Valve 
Diam. 

-s 

85 

SS 

§5 

-i 

§5 

§S 

15 

15 

?S" 

II 

Si50 

3  K 
88  ,D 

II 

ST 
II 

35 

II 

II 

3.8 

3J 

II 

2 

2* 
3 
3* 
4 
4* 

.079 
.098 
.118 
.138 
.157 
.177 

.071 
.088 
.106 
.124 
.141 
.159 

.064 
.080 
096 
.113 
.129 
.145 

.059 
.074 
.088 
.103 
.118 
.133 

.057 
.071 
.085 
.099 
.113 
.127 

.054 
.068 
.082 
.095 
.109 
.122 

.051 
.063 
.076 
.088 
.101 
.114 

.047 
.059 
.071 
.083 
.094 
.106 

.044 
.055 
.066 
.077 
.088 
.099 

.042 
.052 
.062 
.073 
.083 
.094 

LBS.     OF    STEAM    DISCHARGED    PER    HOUR,     BY    BEVEL-SEATED    VALVES    AT    LIFTS 

GIVEN    ABOVE 


2 

730 

1067 

1,332 

1,56S 

1,844 

2,058 

2,237 

2,231 

2,435 

2,565 

2* 

1132 

1654 

2,081 

2,459 

2,871 

3,240 

3,455 

3,658 

3,804 

3,970 

3 

1636 

2390 

2,997 

•  3,508 

4,125 

4,698 

5,001 

5,283 

5,478 

5,679 

3£ 

2232 

3263 

4,116 

4,790 

5,605 

6,337 

6,756 

7,205 

7,457 

7,802 

2902 

4240 

5,370 

6,272 

7,311 

8,310 

8,860 

9,325 

9,739 

10,136 

4* 

3681 

5379 

6,790 

7,953 

9,244 

10,463 

11,252 

11,830 

12,326 

12,918 

LBS.     OF     STEAM     DISCHARGED     PER    HOUR,     BY     FLAT-SEATED     VALVES,     AT    LIFTS 

GIVEN    ABOVE 


ft 

1115 

1633 

2,040 

2,406 

2,830 

3,161 

3,438 

3,586 

3,749 

3,952 

2| 

1729 

2530 

3,188 

3,771 

4,407 

4,976 

5,310 

5,628 

5,858 

6,115 

3 

2498 

3657 

4,591 

5,382 

6,331 

7,201 

7,687 

8,128 

8,434 

8,749 

3^ 

3408 

4991 

6,305 

7,349 

8,604 

9,733 

10,384 

11,086 

11,482 

12,020 

4431 

6485 

8,226 

9,622 

11,222 

12,762 

13,620 

14,346 

14,995 

15,618 

4^ 

5620 

8228 

10,402 

12,200 

14,189 

16,070 

17,295 

18,201 

18,979 

19,900 

The  formulae  for  discharge,  used  in  computing  the  table  are  for  flat-seated 


valves,  JF  =  1.107rDZXX3600;  for  bevel-seated  valves,  W  =  (2.22DI  +  1.1W)  X 

p 

jrrrX36CO;    W  =  lbs.  steam    per  hour;    D  =  diam.  of  valve,  ins.;    Z=lift,  ins.; 

P  =  absolute  pressure,  Ibs.  per  sq.in. 


The  discharge  capacity  of  a  flat  seat  valve  is  1.41  times  that  of 
a  45°  bevel  seat  valve  of  the  same  diameter  and  lift. 

Safety  Valve  Requirements.  Each  boiler  shall  have  two  or  more 
safety  valves,  except  a  boiler  for  which  one  safety  valve  3-in.  size  or 
smaller  is  required  by  these  Rules. 

The  safety  valve  capacity  for  each  boiler  shall  be  such  that  the 
safety  valve  or  valves  will  discharge  all  the  steam  that  can  be  generated 
by  the  boiler  without  allowing  the  pressure  to  rise  more  than  6% 


472 


STEAM-BOILER  ECONOMY. 


CAPACITIES  OF  SAFETY  VALVES 

Discharge  Capacities  of  Direct  Spring-loaded  Pop  Safety  Valves  with  45°  Bevel 
Seats.     Pounds  per  Hour. 


Gage 

Diam. 

lin. 

1X2  in. 

2  in. 

Wn. 

Pres. 

Lbs. 

per 

Lift, 

Vlin. 

Int. 

Max. 

Min. 

Int. 

Max. 

Min. 

Int. 

Max. 

Min 

Int. 

Max. 

Sq.in. 

in 

3.02 

0.04 

0.05 

0.03 

0.05 

0.06 

0.04 

0.06 

0.07 

0.04 

0.06 

0.08 

15 

65 

131 

163 

146 

245 

293 

261 

391 

456 

326 

488 

651 

25 

87 

174 

218 

196 

326 

392 

349 

523 

610 

435 

653 

871 

50 

142 

284 

354 

320 

532 

639 

568 

851 

994 

71C 

1064 

1419 

75 

197 

393 

492 

443 

738 

886 

787 

1181 

1377 

984 

1475 

1968 

100 

252 

503 

629 

566 

944 

1133 

1007 

1510 

1761 

1258 

1887 

2516 

125 

307 

613 

767 

689 

1149 

1379 

1224 

1836 

2145 

1532 

2299 

3064 

150 

362 

723 

904 

813 

1355 

1625 

1438 

2158 

2529 

180€ 

2710 

3613 

175 

416 

833 

1040 

936 

1561 

1872 

1664 

2497 

2913 

2081 

3121 

4161 

200 

471 

941 

1178 

1060 

1766 

2119 

1884 

2826 

3296 

2354 

3532 

4709 

225 

526 

1052 

1315 

1183 

1972 

2366 

2104 

3154 

3680 

262S 

3944 

5258 

250 

581 

1161 

1451 

1307 

2177 

2613 

2322 

3484 

4064 

2903 

4355 

5807 

275 

635 

1271 

1589 

1430 

2383 

2860 

2542 

3813 

4448 

3177 

4766 

6355 

300 

698 

1397 

1746 

1553 

2589 

3107 

2762 

4143 

4832 

3452 

5177 

6903 

Gage 

Diam.  3  in. 

Diam.  3^  ins. 

Diam.  4  ins. 

Diam.  4H  ins.  , 

Press. 

Lbs. 
per 

SJMin 

Int 

Max. 

Min. 

Int. 

Max. 

Min. 

Int. 

Max. 

Min. 

Int. 

Max. 

Sq.in. 

^  (O.Oi 

>O.OS 

0.10 

0.06 

0.09 

0.11 

0.07 

0.10 

0.12 

0.08 

0.11 

0.13 

15 

489 

782 

977 

684 

1,026 

1,254 

912 

1,303 

1,564 

1,173 

1,613 

1,906 

25 

653 

1046 

1,307 

914 

1,372 

1,676 

1219 

1,742 

2,090 

1,568 

2,156 

2,547 

50 

1064 

1703 

2,129 

1490 

2,235 

2,732 

1987 

2,839 

3,406 

2,555 

3,513 

4,151 

75 

1475 

2361 

2,951 

2066 

3,099 

3,788 

2754 

3,935 

4,722 

3,542 

4,870 

5,756 

100 

1887 

3019 

3,774 

2642 

3,963 

4,843 

3522 

5,032 

6,038  . 

4,529 

6,227 

7,358 

125 

2299 

3677 

4,596 

3218 

4,826 

5,899 

4290 

6,128 

7,354 

5,516 

7,583 

8,963 

150 

2710 

4335 

5,419 

3794 

5,690 

6,954 

5058 

7,226 

8,670 

6,503 

8,940 

10,566 

175 

3121 

4993 

6,242 

4369 

6,553 

8,010 

5824 

8,320 

9,984 

7,490 

10,298 

12,173 

200 

3532 

5651 

7,064 

4946 

7,418 

9,068 

6593 

9,420 

11,305 

8,475 

11,655 

13,773 

225 

3944 

631C 

7,890 

5521 

8,280 

10,120 

7361 

10,514 

12,616 

9,465 

13.013 

15.383 

250 

4355 

6968 

8,708 

6097 

9,143 

11,175 

8130 

11,614 

13,938 

10,448 

14,366 

16,980 

275 

4766 

762C 

9,533 

6672 

10.005 

12,333 

8895 

12,707 

15,248. 

11,438 

15,728 

18,585 

300 

5177 

828C 

10,358 

7248 

10,875 

13,290 

9668 

13,807 

16,568 

12,428 

17,088 

20,195 

Valves  \Vt,  in.  diam.  with  lifts  0.03,  0.04  and  0.05  in.  give  a  discharge  for  0.04  in.  lift  the  same 
as  that  of  a  1-in.  valve  with  0.05  in.  lift;  with  0.03  in.  lift  25%  less  and  with  0.05  in.  lift  25% 
greater. 

above  the  maximum  allowable  working  pressure,  or  more  than  6% 
above  the  highest  pressure  to  which  any  valve  is  set. 

One  or  more  safety  valves  on  every  boiler  shall  be  set  at  or  below 
the  maximum  allowable  working  pressure.  The  remaining  valves 
may  be  set  within  a  range  of  3%  above  the  maximum  allowable  work- 
ing pressure,  but  the  range  of  setting  of  all  of  the  valves  on  a  boiler 
shall  not  exceed  10%  of  the  highest  pressure  to  which  any  valve  is 
set. 

Safety  valves  shall  be  of  the  direct  spring-loaded  pop  type.  The 
vertical  lift  of  the  valve  disc  may  be  made  any  amount  desired  up  to 
a  maximum  of  0.15  in.  The  diameter  measured  at  the  inner  edge  of 
the  valve  seat  shall  be  not  less  than  1  in.  or  more  than 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.  473 

Each  safety  valve  shall  have  plainly  stamped  or  cast  on  the  body: 
(a)  The  name  or  trade-mark  of  the  manufacturer,  (b)  The  nominal 
diameter  with  the  words  "Bevel  Seat"  or  "Flat  Seat,"  (c)  The  steam 
pressure  at  which  it  is  set  to  blow,  (d)  The  lift  of  the  valve  disc  from 
its  seat,  measured  immediately  after  the  sudden  lift  due  to  the  pop, 
(e)  The  weight  of  steam  discharged  in  pounds  per  hour  at  the  pres- 
sure for  which  it  is  set  to  blow. 

The  minimum  capacity  of  a  safety  valve  or  valves  to  be  placed 
on  a  boiler  shall  be  determined  on  the  basis  of  6  Ibs.  of  steam  per 
hour  per  sq.  ft.  of  boiler  heating  surface  for  water  tube  boilers,  and 
5  Ibs.  for  all  other  types  of  power  boilers,  and  upon  the  relieving 
capacity  marked  on  the  valves  by  the  manufacturer,  provided  such 
marked  capacity  does  not  exceed  that  given  in  the  table,  in  which 
case  the  minimum  safety  valve  capacity  shall  be  determined  on  the 
basis  of  the  maximum  relieving  capacity  given  in  the  table  for  the 
particular  size  of  valve  and  working  pressure  for  which  it  was  con- 
structed. The  heating  surface  shall  be  computed  for  that  side  of  the 
boiler  surface  exposed  to  the  products  of  combustion,  exclusive  of 
the  superheating  surface. 

Safety  Valves  for  Locomotives. — A  committee  of  the  American 
Railway  Master  Mechanics'  Association  presented  a  report  on  safety 
valves  in  1912,  giving  the  following  formula  for  45°  bevel  seat  valves. 
DLP  —  0.036IT,  in  which  D  —  total  of  the  diameters  of  the  inner 
edge  of  the  seats  of  the  valves  required ;  L  =  vertical  lift  in  inches ; 
P  =  absolute  pressure  Ibs.  per  sq.  in. ;  H  =  total  heating  surface  of 
boiler  sq.  ft.  (superheating  surface  not  included).  Every  locomotive 
should  be  equipped  with  not  less  than  two  and  not  more  than  three 
safety  valves,  the  size  to  be  determined  by  the  formula.  The  valves 
are  to  be  set  as  follows :  The  first  at  boiler  pressure,  second  2 
Ibs.  in  excess,  third  3  Ibs.  in  excess  of  second.  Manufacturers  should 
be  required  to  stamp  on  the  valve  the  lift  in  inches  as  determined  by 
actual  test. 

The  formula  corresponds  to  the  discharge  calculated  by  Napier's 
rule  with  a  coefficient  of  flow  of  0.973  and  an  evaporation  of  4  Ibs. 
per  square  foot  of  heating  surface  per  hour.  It  is  evident  that  safety 
valves  proportioned  according  to  this  formula  will  have  a  relieving 
capacity  much  less  than  the  evaporative  capacity  of  a  locomotive  boiler 
with  large  fire-boxes  and  short  flues.  The  Consolidated  Safety 
Valve  Co.  suggests  the  formula  DLP  =  C1H1+C2H2  in  which  Hx 
is  fire-box  and  IL,  flue  heating  surface,  sq.  ft.,  and  Cx  and  C2  are 


474 


STEAM-BOILER  ECONOMY. 


constants  to  be  determined  by  experiment,   C±  being  considerably 
larger  than  C2 

Damper  Regulators. — For  the  purpose  of  automatically  varying 
the  force  of  draft  with  the  demand  for  steam,  damper  regulators  are 
in  common  use.  They  are  operated  by  the  steam  pressure,  and  when 
this  rises  above  a  desired  point  they  close,  more  or  less,  the  flue 
damper,  and  open  it  when  the  pressure  falls.  There  are  many  different 
varieties  in  the  market.  One  form  is  shown 
in  Fig.  203.  It  consists  of  a  brass  cylinder 
in  which  is  a  piston  connected  to  a  spring, 
which  balances  the  steam  pressure.  Con- 
densed steam  from  the  boiler  is  admitted 
under  the  piston.  The  spring  is  in  a  separate 
chamber,  so  that  no  steam  or  water  can 
come  in  contact  with  it.  Steam  is  admitted 


FIG.  203.— DAMPER  REG- 
ULATOR. 


FIG.  204. — FEED-WATER  REGULATOR 
AND  ALARM  COLUMN. 


to  the  pipe,  at  the  bottom,  and  any  variation  in  pressure  results  in  a 
movement  of  the  piston  and  rod  so  that  the  damper  is  opened  or  closed 
in  proportion  to  the  change  in  pressure.  Connection  is  made  direct, 
when  possible,  but  if  not,  a  rocker  shaft  made  of  piping  may  be  used 
to  transmit  the  motion. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM   APPLIANCES.    475 

Feed-water  Regulator. — A  combined  feed-water  regulator  and 
alarm-water  column  is  shown  in  Fig.  204.  Control  of  the  feed-water 
supply  is  effected  by  a  valve  placed  at  the  bottom,  which  controls  the 
action  of  the  pump  by  means  of  a  back  pressure  regulator,  which  is 
placed  in  the  -steam  pipe  of  the  pump  and  regulates  the  pressure  in 
the  water  main  from  the  pump  to  the  boiler.  By  this  arrangement 
the  pump  cannot  cause  an  excessive  pressure  in  the  water  main  if  the 
boiler  should  take  but  little  water  for  a  period  of  time.  The  valve 
at  the  bottom  of  the  regulator  is  connected  by  means  of  levers  to  a 
cast  bronze  float  made  in  one  piece  and  copper  plated,  so  that  it  can- 
not collapse  or  become  waterlogged.  This  float  opens  and  closes  the 
valve  according  to  the  requirements  of  the  boiler,  so  that  the  water 
level  is  maintained  at  a  nearly  constant  height  and  cannot  fall  more 
than  two  inches  below  that  desired  without  sounding  the  alarm.  Gauge 
cocks  and  a  gauge  glass  are  placed  on  the  drum  of  the  regulator.  The 
apparatus  should  be  blown  out  frequently  to  make  sure  that  it  is  clear 
of  obstructions.  Where  it  is  used  in  connection  with  a  battery  of 
boilers,  one  of  the  water  columns  is  used  on  each  boiler. 

The  Copes  Feed-water  Regulator. — Fig.  205  represents  diagram- 
matically  the  Copes  submerged  tube  regulator.  It  consists  essentially 


FIG.  205. — DIAGRAM  OF  THE  COPES  FEED-WATER  REGULATOR. 

of  an  inclined  thermostatic  tube  which  controls  the  opening  of  a 
balanced  valve  in  the  feed-pipe.  The  maximum  and  minimum  heights 
at  which  it  is  deemed  safe  to  carry  the  water  levels  are  first  decided 
upon  and  then  the  thermostat  is  installed  with  sufficient  slope  so 
that  when  the  water  level  is  at  its  minimum  height,  there  is  no 
water  in  the  expansion  tube,  and  when  the  level  is  at  the  maximum 
height,  the  tube  is  filled  with  water.  The  level  in  the  tube  fluctuates 
with  the  level  in  the  boiler. 


476 


STEAM-BOILER  ECONOMY. 


The  operation  of  the  regulator  is  as  follows:  Suppose  the  level 
is  at  the  middle  gauge  (No.  2  in  Fig.  205)  and  the  boiler  load  is  100%. 
The  expansion  tube  is  half  submerged,  and  has  a  length  correspond- 
ing. When  an  increased  load  comes  on,  with  a  slight  drop  in  steam 
pressure,  accompanied  by  a  more  rapid  liberation  of  steam,  a  rise 
takes  place  in  the  boiler  water  level.  This  raises  the  level  of  the 
water  in  the  expansion  tube  slightly,  decreases  its  temperature,  caus- 
ing the  tube  thereby  to  shorten  and  the  valve  to  shut,  decreasing 
the  rate  of  feed  to  the  boiler.  This  is  desired  in  order  to  obtain 
the  maximum  capacity  of  the  boiler,  since  the  heat  being  generated 
in  the  furnace  is  used  to  generate  steam  and  not  to  heat  feed  water 
at  a  time  when  every  pound  of  steam  counts.  As  the  heavy  load  con- 
tinues, the  evaporation  of  water  causes  the  level  to  drop  and  this 
causes  expansion  of  the  thermostat  and  gradual  opening  of  the  feed 
valve.  The  level  in  the  boiler  drops  and  the  feed  valve  opens 
until  a  point  is  reached  where  the  rate  of  feed  equals  the  rate  of 
evaporation  and  equilibrium  is  restored,  the  water  being  at  a  new 
level. 

A  decrease  in  load  means  a  smaller  steam  demand,  and  a  rise 
in  boiler  pressure,  and  the  water  level  falls  slightly,  with  a  heating 
up  and  expansion  of  the  thermostat.  This  causes  the  feed  valve  to 
open  wider  and  feed  the  water  at  a  greater  rate  to  the  boiler,  thus 
absorbing  and  storing  heat.  A  decreasing  load  is  then  accompanied 
by  a  rising  water  level.  This  cools  the  expansion  tube  and  slowly 
cuts  down  the  feed  again,  so  that  at  any  fixed  load  position  the  rate 
of  feed  finally  becomes  just  equal  to  the  rate  of  evaporation,  and 
equilibrium  is  again  secured,  the  water  level 
now  standing  in  the  boiler  at  a  somewhat 
greater  height  than  it  did  'at  the  normal  load. 
Every  load  on  the  boiler  has  some  correspond- 
ing proper  water  level  which  the  regulator 
maintains. 

Blow-off  Valve. — The  blow-off  valve  at  the 
bottom  of  a  boiler  or  of  a  mud-drum  is  sub- 
jected to  severe  service  on  account  of  its  dis- 
charging particles  of  scale  and  mud  which  cause 
wear  of  the  seat.  When  the  valve  is  screwed 
down  particles  of  scale  are  apt  to  be  caught 
between  the  valve  and  the  seat,  damaging  them 
and  causing  leaks.  For  this  reason  blow-off 

valves  are  usually  constructed  with  removable 
FIG.  206.— BLOW-OFF      ,.  ,  -,  -«.        OA~     ,  .  . 

VALVE  disks   and   seats,      .tig.    206   shows   a   lorm   01 

blow-off  valve.     The  valve  plug  or  piston  may 
be  lifted  by  the  screw  stem  so  as  to  give  a  full  opening  for  the  escape 


BOILER  ATTACHMENTS  AND  BOILER-ROOM   APPLIANCES.    477 


FIG.  207. — CONTINUOUS  SURFACE 
BLOW-OFF. 


.of  scale  and  other  impurities..  The  valve  or  disk  seats  on  a  ring  fitted 
into  the  casing  and  the  disk  and  ring  may  readily  be  removed  for 
repairs  or  renewal. 

Surface  Blow-off. — Many  scale-forming  materials  when  precipi- 
tated from  solution  or  formed  by  evaporation  float  at  first  as  scum 
on  the  surface  of  the  water  in  the  boiler,  from  which  they  may  be 
removed  directly  by  means  of  a  surface  blow-off.  This  consists  of 
a  funnel  with  a  rectangular  mouthpiece  extending  across  the  width 

of  the  boiler  at  the  water  line, 
so  placed  as  to  receive  the  sur- 
face current  of  water,  connected 
by  a  pipe  to  a  valve  outside 
the  boiler,  through  which  the 
scum  collected  in  the  funnel 
may  be  discharged.  Automatic 
skimming  devices  are  some- 
times used,  which  keep  up  a 
circulation  of  water  from  the 
skimming  funnel  through  a  set- 
tling chamber  or  a  filter,  from 
which  the  water  is  returned  to  the  boiler.  The  Hotchkiss  "boiler 
cleaner/'  one  of  this  type,  is  shown  in  Fig.  207.  The  settling-chamber 
is  placed  above  the  boiler.  When  the  valves  PI  and  H  are  opened, 
steam  rises  through  both  pipes  (the 
valve  F  at  first  being  open  to  allow 
escape  of  air)  until  it  fills  the  chamber 
B.  This  steam  condenses,  and,  be- 
cause of  the  partial  vacuum  thus 
formed,  water  rises  and  finally  fills 
the  chamber.  Then  the  circulation  be- 
gins, the  dirt-laden  water  rising  along 
the  pipe  D,  and,  after  passing  through 
the  chamber  B,  where  much  of  this  FIG.  208.— DEVICE  FOR  ADMITTING 
sediment  drops  to  the  bottom,  con-  R> 

tinues  its  course  back  into  the  boiler  through  the  pipe  E.  The  valve 
F  is  occasionally  opened,  which  discharges  the  dirt  from  the  bottom  of 
the  chamber  B. 

Regulating  the  Air  Supply  over  the  Fire. — Fig.  208  shows  a  device 
patented  by  Cliff  in  1855  for  admitting  air  through  a  furnace  door 
immediately  after  firing  and  gradually  shutting  it  off  as  the  smoky 


478  STEAM-BOILER  ECONOMY. 

gases  distilled,  from  the  coal  decreased.  As  the  door  was  opened  the 
hollow  piston  in  the  adjoining  cylinder  dropped  into  the  water  in  the 
bottom  of  the  cylinder,  which  water  ran  through  an  upward  opening 
valve  into  the  piston. 

As  the  door  was  closed  after  firing  the  attached  chain  caused 
the  piston  to  rise,,  carrying  its  load  of  water  with  it,  the  valve 
being  closed.  The  weight  of  the  water  and  piston  caused  the 
shutter  to  move  up  and  open  wide,  and  as  the  water  ran  out  of  the 
piston  the  weight  of  the  slide  (and  a  counter  weight)  caused  the 
slide  to  move  down  slowly,  thus  gradually  closing  the  openings  until, 
when  the  piston  was  empty,  the  secondary  air  supply  was  entirely 
cut  off. 

Many  similar  devices  have  been  used  in  recent  times,  using  air 
instead  of  water  in  the  cylinder.  In  these  the  opening  of  the  door 
raised  a  weighted  piston  and  opened  the.1  slides  in  the  door,  and  after 
the  door  was  closed  the  air  beneath  the  piston  leaked  around  it  into 
the  chamber  above  while  the  piston  gradually  descended  and  closed 
the  slides. 

The  ordinary  pneumatic  or  compressed-air  "door-check"  has  been 
successfully  used  for  this  purpose.  It  may  be  arranged  to  slowly  close 
either  the  door  itself  or  an  air  valve  in  the  door.  It  acts  by  prevent- 
ing the  door  from  being  entirely  closed  immediately  after  firing,  until 
air,  which  has  been  compressed  in  the  device  by  the  opening  of  the 
door,  leaks  out  of  it. 

Water-tube  Cleaner. — Fig.  209  shows  a  tool  used  for  removing 
scale  from  the  tubes  of  a  water-tube  boiler.  It  consists  of  a  small 
water  turbine,  using  water  supplied  at  about  100  pounds  per  square 

inch  through  a  hose  from  a  pump, 
rotating  at  high  speed  a  shaft  and 
a  series  of  arms  carrying  hardened 
steel  cutters.  The  tool  is  pushed 
back  and  forth  through  the  tubes 

and    the   water   from   the   turbine 

FIG.  209. — TURBINE  WATER-TUBE  ,-.       -i         -j.  41    4.  v 

CLEANER.  washes  away  the  deposit  that  has 

been  loosened  by  the  cutters. 

Steam  Separators. — There  are  many  different  forms  of  separators 
in  the  market,  one  of  which  is  shown  in  Fig.  210.  Steam  enters  at 
the  top  and  passes  around  the  sides  of  the  inclined  baffles,  which  catch 
the  "entrained"  water  and  divert  it  to  the  chamber  below,  whence  it 
is  removed  by  a  trap. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    479 


Another  form  of  steam  separator  is  shown  in  Fig.  2Wa.     The 
steam  is  given  a  whirling  motion  by  the  helical  baffle  in  the  pipe, 

forcing  the  drops  of  water  to  the  circum- 
ference, where  it  escapes  at  the  edge  of 
the  opening  leading  to  the  water  chamber 
beneath. 


FIG.  210.— STEAM  SEPARATOR. 


FIG.  210a. — STEAM  SEPARATOR. 


High-  and  Low-water  Alarm. — Fig.  211  shows  a  common  form  of 
water  column,  provided  with  a  high-  and  low-water  alarm.    The  float, 

usually  made  of  copper,  operates  a 
steam  whistle  whenever  the  water 
gets  too  high  or  too  low.  The  three 
threaded  holes  on  each  side  are  for 
the  attachment  of  gauge  cocks  on 
either  side  of  the  column,  those  on 
the  other  side  being  plugged. 

Gauge  Glass  and  Gauge  Cocks. — 
Every  boiler  should  be  provided  both 
with  a  gauge  glass  to  indicate  the 
height  of  the  water  level,  and  three 
gauge  cocks,  the  middle  one  set  at 
the  desired  water  level  and  the  other 
two  at  the  highest  and  lowest  al- 
lowed levels.  These  should  be  open- 
ed frequently  as  a  check  on  the 

indications  of  the  gauge  glass,  which 
Fio.211.-SAF.TT  WATER  COLUMN.    Qn  account  Qf  ck)gging  Qf  ^  cQn_ 

nections  may  indicate  a  false  level.  They  are  usually  connected  to  a 
water  column,  as  in  Fig.  212.  For  water-tube  boilers  the  valves  of 
the  gauge  cocks  are  usually  closed  by  weights,  which  are  lifted  by 
long  rods  easily  reached  by  the  fireman. 


^i-A  Water  Gage 


Water 
Connection 


480 


STEAM-BOILER  ECONOMY. 


Steam  Gauges. — The  .Bourdon  spring  steam  gauge  is  in  universal 
use  for  steam  boilers.  It  depends  on  the  principle  that  a  bent  tube 
subjected  to  internal  pressure  tends  to  straighten  out.  The  tube  is 

usually  made  of  brass,  somewhat  flat- 
tened, closed  at  one  end,  and  bent  into 
a  C-shape.  The  open  end  is  connected 
to  a  pipe  leading  from  the  boiler,  and 
the  movement  of  the  closed  end  is 
multiplied  by  a  pinion  and  sector 
mechanism,  so  as  to  move  an  index  on 
a  dial.  The  dial  is  calibrated  by  com- 
paring its  indications  with  those  of 
a  mercury  column.  The  piping  lead- 
ing to  the  gauge  should  be  as  short 


FIG.  212. — WATER  COLUMN,  GAUGE 
GLASS  AND  GAUGE  COCKS. 


FIG. 


213.— STEAM  GAUGE  CON- 
NECTIONS. 


and  direct  as  possible.  No  valves  or  stop  cocks  are  used  other  than  the 
cock  at  the  gauge.  Piping  should  be  no  smaller  than  the  fitting  on 
the  gauge  and  should  be  so  arranged  that  there  will  be  a  water  pocket 
next  the  gauge,  thus  preventing  the  steam  from  coming  in  contact 
with  the  bent  tube  and,  by  its  heat,  so  altering  the  temper  of  the  tube 
as  to  make  the  reading  inaccurate.  Methods  of  doing  this  are  shown 
in  Fig.  213. 

The  Venturi  Meter. — When  water  flows  through  a  pipe  contain- 
ing a  contraction,  like  Fig.  214,  the  pressure  at  the  throat  B  is  less 
than  at  the  inlet  A,  due  to  the  increased  velocity  at  B.  In  a  prop- 
erly proportioned  pipe  this  loss  of  pressure  is  almost  entirely  re- 
gained at  the  outlet  C.  These  facts  may  be  proved  by  inserting 
pressure  gauges  at  A,  B  and  (7.  Practically  the  same  amount  of  water 
therefore  will  be  delivered  through  such  a  tube  as  through  a  length 
of  straight  pipe  of  equal  length  and  diameter  under  the  same  work- 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.     481 


ByPassCock- 

A 

J 


A  B 


D  Air  Valves 


.Glass  Tubes 


ing  pressure.  The  temporary  loss  of  pressure  at  B  can  be  measured 
by  a  U-tube  containing  mercury,  and  it  is  found  to  increase  ap- 
proximately as  the  square  of  the  throat  velocity — that  is  to  say, 
if  the  velocity  of  the  water  at  B  doubles, 
the  difference  of  mercury  levels  becomes 
about  four  times  as  great.  Mr.  Clemens 
Herschel  in  1887  invented  the  Venturi 
meter,  based  upon  the  phenomenon  above 
described.  The  Builders  Iron  Foundry, 
Providence,  R.  I.,  has  perfected  many  dif- 
ferent types  of  indicating,  recording  and 
registering  instruments  for  use  with  the 
Venturi  tube.  Fig.  215  shows  an  indicating 
manometer  commonly  used  with  the  meter, 
when  used  for  measuring  boiler  feed-water. 


c 

Air  Chambers 


Graduated^ 

Scale 


f-Q   Valves 
Drain  Valves 


FIG.  214.— THE  VENTURI  METER. 


FIG.  215. — MANOMETER  i 
VENTURI  METER. 


The  V-Notch  Water  Meter. — When  water  flows  over  a  sharp- 
edged  V-shaped  notch,  whose  sides  are  at  an  angle  of  90°,  the 
amount  of  water  flowing  may_be  computed  by  the  formula:  Cubic 
feet  per  minute  =  0.305//2 V/f ,  in  which  H  is  the  height  in  inches 
of  the  level  of  still  water  behind  the  notch  measured  above  the  level 
of  the  bottom  of  the  notch.  A  paper  by  D.  Robert  Yarnall,  in 
Trans.  A.  S.  M.  E.,  1912,  gives  the  results  of  tests  of  a  recording 
water  meter  made  on  this  principle,  which  showed  an  average  error 
of  less  than  0.5  per  cent.  Fig.  216  shaws  a  recording  hot-water  meter 
of  this  type,  built  in  connection  with  a  Cochrane  feed-water  heater, 
made  by  Harrison  Safety  Boiler  Works.  The  level  of  the  water 
behind  the  notch  is  transferred  by  a  tube  to  the  cylinder  shown  in 
the  chamber  at  the  left,  which  contains  a  float,  the  vertical  rod  from 
which  actuates  a  rod  on  a  clock  recording  apparatus  contained  in 
the  case  above. 

Feed-water  Indicators. — Fig.  217  shows  the  Pi  tot-tube  method 
of  indicating  the  flow  of  water  in  pipes.  A  and  B  are  two  14-inch 
tubes  fixed  in  the  pipe  and  bent  so  that  the  portion  parallel  to  the 
axis  is  at  the  middle  of  the  pipe  and  pointing  opposite  the  direction 


482 


STEAM-BOILER  ECONOMY. 


of  flow.    A  is  open  at  the  end,  with  the  orifice,,  a  thin  edge,  at  right 
angles  to  the  axis  of  the  pipe.     B  is  closed  at  the  end  and  has  two 


FIG.  216.  —  V-NOTCH  METER  IN  A  COCHRANE  HEATER. 

or  more  small  holes  bored  in  it,  on  each  side,  some  distance  back 
from  the  end,  the  face  of  their  openings  being  smooth  and  parallel 

to  the  direction  of  flow  in  the  pipe. 
C  and  D,  the  prolongations  of 
these  tubes,  are  each  connected  to 
mercury  tube  gauges.  The  gauge 
connected  with  A  registers  the 
total,  or  impact  pressure,  and  that 
connected  with  B  the  static  press- 
ure. The  difference  is  the  velocity 
pressure  in  inches  of  mercury, 
which  is  converted  into  feet  head 
of  water  by  multiplying  by  1.134. 
The  corresponding  velocity  is 
found  by  the  formula  V  =  \ 


FIG.  217.—  PITOT-TUBE  MEASUREMENT,  but   as    this    is    the    velocity   at 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    483 

the  center  of  the  pipe  only  it  must  be  multiplied  by  a  coefficient, 
usually  from  0.87  to  0.91,  which  is  determined  by  calibration  with 
a  tank. 

Filtering  Oil  from  Feed- water. — Fig.  218  shows  a  filter  for  re- 
moving oil  from  feed-water,  made  by  the  Ross  Valve  Co.,  Troy,  N.  Y. 
The  filter  is  placed  between  the  feed  pumps  and  the  boiler.  It  con- 
sists essentially  of  a  chamber  containing  a  bag  made  of  "Turkish 


Feed 


FIG.  218. — FEED-WATER  FILTER. 

toweling,"  so  folded  as  to  obtain  a  large  area  of  filtering  surface 
in  a  small  space.  The  surface  of  the  bag  is  formed  into  a  series  of 
deep  circular  corrugations  by  being  thrown  over  a  bronze  skeleton, 
and  drawn  down  between  the  sections  by  strings  wound  around  it. 
The  filtering  surface  is  from  250  to  1000  times  the  area  of  the  feed 
pipe,  according  to  the  service  required.  The  threads  of  the  Turkish 
toweling  retain  the  oil  until  they  become  saturated  with  it,  while  they 
let  the  water  pass  through.  The  filter  may  be  cleaned  by  reversing 
the  direction  of  the  current,  allowing  the  wash  water  to  run  to  waste, 
or  by  changing  the  filter  bag,  a  fresh  one  always  being  kept  in  reserve. 
Pressure  gauges  are  placed  near  both  inlet  and  outlet,  and  when  the 


484 


STEAM-BOILER  ECONOMY. 


difference  in  pressure  at  a  given  rate  of  flow  becomes  excessive  it 
indicates  that  the  filter  bag  is  clogged  and  should  be  cleaned  or 
changed. 

Steam  Meters. — Fig.  219  shows  an  elementary  form  of  indicating 
steam-flow  meter  based  upon  the  Pitot  tube.  A  and  C  are  two 
ordinary  gauge-cocks  and  G  is  a  gauge-glass;  C  being  connected 
with  the  static  nozzle  S,  and  A  with  the  dynamic  tube  D.  The 
height  of  water  H  is  proportional  to  the  square  of  the  velocity  of 


FIG.  219. — PITOT-TUBE  STEAM 
METER. 


FIG.  220.— PITOT  TUBE  WITH 
MERCURY  MANOMETER. 


steam  flowing  through  the  pipe  P  and  automatically  adjusts  itself 
to  the  variations  in  velocity;  thus,  for  decreasing  velocities,  the 
water  in  glass  G  discharges  through  D  until  the  water  column  H 
balances  the  velocity  pressure  in  pipe  P,  and  for  increasing  velocities, 
condensation  from  the  upper  part  of  the  instrument  accumulates 
and  the  water  column  .H  rises  until  a  balance  is  effected  for  the 
higher  velocities. 

According  to  Gebhardt,  this  device  in  connection  with  a  cali- 
brated scale  gives  readings  within  5  per  cent  of  condenser  measure- 
ments for  continuous  flow  and  constant  pressure  and  quality  of 
steam,  but  for  varying  flow  and  pressure  its  indications  are  not 
reliable.  Fig.  220  shows  a  Pitot-tube  steam  meter  in  which  a  mercury 
manometer  is  used  for  indicating  the  velocity.  S  is  the  static  nozzle 
at  right  angles  to  and  D  the  dynamic  nozzle  facing  the  current;  U 
is  an  ordinary  IT- tube  manometer  partially  filleVi  with  mercury. 
When  there  is  no  flow  the  surface  of  the  mercury  in  the  columns 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    485 

N  and  W  will  be  on  the  same  level  and  the  upper  portions  will  be 
filled  with  condensed  vapor.  When  there  is  a  flow,  the  mercury 
will  be  depressed  as  indicated  and  the  difference  H  in  the  heights 
of  the  mercury  columns  will  be  a  measure  of  the  velocity  of  flow 
at  the  point  in  the  pipe  where  the  dynamic  tube  is  placed. 

This  velocity  may  be  expressed  by  substituting  the  proper  values 
in  the  equation 

V  = 

in  which  h  —  height  of  the  mercury  column  H.,  Jc  =  an  experimen- 
tal coefficient,  ds  =  density  of  steam  in  the  main  pipe,  dm  =  den- 
sity of  the  mercury  in  pounds  per  cubic  foot.  The  mercury  manom- 
eter is  less  sensitive  than  the  water  manometer  by  VlS.6  or  approxi- 
mately 3.7.  The  variable  height  of  the  water  column  above  the  mer- 
cury is  included  in  the  value  of  the  coefficient  K. 

The  General  Electric  Co.  makes  a  number  of  steam  meters  of 
the  Pitot-tube  type.  Three  styles  are  manufactured:  (1),  one  in 
which  the  velocity  pressure  is  measured  directly  by  means  of  a 
U-tube  manometer;  (2)  one  in  which  the  variation  in  the  height 
of  the  mercury  is  transmitted  to  an  indicating  dial  through  the 
agency  of  floats  and  pulleys,  and  (3)  one  in  which  the  variation  in 
the  weight  of  the  mercury  column  actuates  a  recording  mechanism 
by  means  of  a  series  of  compound  levers.  A  nozzle  plug,  shown  in 
Fig.  221,  is  used  in  place  of  the  ordinary  static  and  dynamic  nozzles. 
TT  are  the  static  openings,  or  "trailing  set,"  and  LL  the  dynamic 
openings  or  "leading  set."  The  plug  is  screwed  into  the  pipe  with 
the  "leading  set"  directly  facing  the  current  and  the  connections 
to  the  manometer  are  made  through  the  openings  T'  and  L' .  The 
weight  of  steam  flowing  may  be  obtained  directly  from  the  height 
of  the  mercury  column  by  means  of  suitable  charts  based  upon 
experiments.  Adjustment  for  variations  in  pressure,  quality  and 
pipe  diameter  are  made  by  setting  the  chart  cylinder  C,  Fig.  223,  in 
accordance  with  the  graduated  scales  at  the  bottom  of  the  instrument. 

For  general  purposes  a  revolving  chart  is  furnished,  the  readings 
of  which,  multiplied  by  the  area  of  the  pipe,  give  the  weight  of 
steam  flowing.  For  low  velocities  the  difference  in  the  heights  of 
the  mercury  columns,  if  vertical,  is  so  small  as  to  lead  to  serious 
error;  hence  provision  is  made  for  this  by  inclining  the  manometer 
as  indicated  in  Fig.  222.  With  this  the  actual  head  of  mercury  due 
to  the  velocity  is  H,  but  the  difference  in  the  lengths  of  the  columns 


486 


STEAM-BOILER  ECONOMY. 


is  D.  The  indication  on  the  chart  corresponding  to  the  height  of 
the  mercury  in  the  glass  T",  multiplied  by  a  constant  depending 
upon  the  inclination  of  the  glass,  is  the  rate  of  flow  in  pounds  per 
hour  per  square  inch  of  the  pipe  cross-section. 

The  accuracy  of  this  meter  depends  upon  the  refinement  of  ad- 
justment and  the  extent  of  error  in  reading  the  height  of  the  mer- 
cury column.  Tests  of  this  instrument,  conducted  at  the  Armour 
Institute  of  Technology,  gave  readings  for  continuous  flow  agreeing 


To"Trailing 


To"Leadmg  Set" 


FIG.  221. — NOZZLE  FOR  STEAM  FLOW 
METER. 


FIG.  222. — INCLINED  MANOMETER. 


FIG.  223. — ADJUSTABLE  CHART 
FOR  STEAM  METER. 


within  1  to  8  per  cent  of  condenser  measurements,  depending  upon 
the  rate  of  flow.  For  interrupted  flow  the  departure  from  condenser 
readings  was  more  marked. 

Eecording  draft  gauges  on  the  inverted  can  principle  (see  Fig. 
251,  page  587),  but  with  the  can  supported  by  a  plunger  floating  in 
mercury  instead  of  by  a  spring,  are  made  by  the  Uehling  Instrument  Co. 

Other  steam  flow  meters  on  the  Pitot-tube  principle  are  described 
in  Bulletin  800  of  James  G.  Biddle,  Philadelphia,  1915,  and  in  Bulle- 
tin No.  3  of  Republic  Flow  Meters  Co.,  Chicago,  1914. 

The  St.  John  Steam  Meter. — Fig.  224  is  a  meter  used  by  the  New 
York  Steam  Co.  to  register  the  steam  used  by  its  customers.  The 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    487 


author  has  used  this  meter  to  measure  the  steam  delivered  by  boilers, 
and  has  also  tested  its  accuracy  at  different  rates  of  flow,  by  means  of  a 
surface  condenser,  and  found  it  to  have 
no  error  greater  than  that  of  the  possi- 
ble error  in  reading  the  height  of  the 
line  on  the  paper  record,  say  0.01  inch, 
equivalent  to  an  error  of  1  per  cent  for 
1  inch  height  above  the  zero  line  of 
the  record,  or  2  per  cent  for  %  inch 
height. 

Steam  enters  the  meter  at  G,  and 
escapes  at  H.  The  tapering  valve  11 , 
with  its  guide  rods  and  piston  head 
standing  vertically  in  casings  A,  B,  S 
and  dashpot  (7,  rises  and  falls,  stands 
high  or  low  in  the  hole  or  seat  23,  and 
increases  or  diminishes  the  annular 
space  between  the  valve  and  seat,  in 
accordance  with  the  flow  of  steam  from  FIG.  224. — THE  ST.  JOHN  STEAM 
GtoA.  METER- 

As  the  valve  rises  and  falls,  the  motion  is  communicated  to  the 
lever   7,  by  its  contact  with  the  valve  at  21,  and   is  then  further 


FIG.  225. — THE  ROBERTS  SMOKE  CHART. 

communicated  to  the  outside  by  the  rocking  of  the  fulcrum  in  a 
stuffing-box  at  14,  and  then  by  a  rod  to  a  roll  of  paper,  driven  by 
clockwork.  This  paper  gives  a  record  of  the  varying  heights  of 


488 


STEAM-BOILER  ECONOMY. 


valve  and  flow  of  steam,  which  flow  is  proportioned  to  the  height. 
The  formula  for  computation  is  based  on  the  flow  of  steam  when 
the  valve  is  one  inch  off  the  seat,  which  is  ascertained  by  actual  test 
by  means  of  a  condenser. 

The  Roberts  Smoke  Chart. — Fig.  225  shows  two  styles  of  smoke 
chart  invented  by  E.  P.  Roberts,  Smoke  Inspector  of  Cleveland,  0., 
which  are  claimed  to  be  more  convenient  in  operation  than  the 
Ringelmann  chart.  They  consist  of  disks  of  cardboard  having  radial 
black  lines  on  a  white  background.  When  a  disk  is  revolved  a  series 
of  tints  appear,  ranging  from  white  at  the  center  to  black  at  the 
edge.  They  are  spun  by  hand  while  supported  on  a  brad-awl  or 
other  convenient  spindle,  an  eyelet  center  being  provided  in  the  disk 
for  the  purpose.  One  of  the  charts,  when  spun,  shows  a  series  of 
rings  corresponding  to  smoke  densities  of  20,  40,  60,  80  and  100 
per  cent.  (For  the  Ringelmann  chart  see  page  588.) 

-  The  Ellison  Differential  Draft  Gauge  is  shown  in  Fig.  226.     It 
consists  of  an  inclined  tube  of  small  caliber  attached  to  a  vertical 


FIG.  226. — ELLISON  DRAFT  GAUGE. 

tube  of  large  diameter,  and  mounted  on  an  aluminum  case,  with  a 
graduated  scale  along  the  inclined  tube.  A  spirit  level  is  attached 
to  the  instrument.  The  liquid  used  is  a  light  non-drying  mineral 
oil  (sp.  gr.  0.834),  and  the  graduations  are  so  made  that  the  figures 
correspond  to  hundredths  of  an  inch  of  water-level.  A  combination 
gauge  is  also  made  in  which  the  lower  end  of  the  inclined  tube 
joins  a  U-tube,  so  that  pressures  up  to  5  inches  of  water  may  be 
measured,  the  graduations  in  the  U-tube  being  tenths  of  an  inch. 

The  Blonck  Differential  Draft  Gauge. — In  a  boiler  plant  con- 
taining several  boilers  it  is  important  to  know  that  each  boiler  is 
doing  its  proper  share  of  the  total  work.  One  means  of  obtaining 
this  knowledge  is  to  have  the  steam  pipe  of  each  boiler  equipped 
with  a  steam  meter.  Another  means  is  to  have  a  feed  pipe  of  each 
boiler  provided  with  an  indicating  water  meter,  such  as  the  Venturi. 
together  with  a  feed-water  regulator  to  keep  the  water  level  constant. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    489 

Still  another  means  is  a  differential  pressure  gauge  which  registers 
a  difference  in  pressure  or  draft  between  the  damper  and  the  fur- 
nace. The  area  for  the  passage  of  the  gases  from  the  furnace  to 
the  flue  damper  being  unchangeable  in  a  given  boiler,  the  amount 
of  gas  flowing  is  proportional  to  the  velocity,  and  the  velocity  de- 
pends on  the  difference  of  pressure  at  the  entrance  and  the  end  of 
the  passage.  If  the  gases  were  of  uniform  temperature  and  pressure, 
the  quantity  flowing  would  be  proportional  to  the  square  root  of 
the  pressure  difference.  This  law  of  proportionality  is  modified  by 
variation  in  the  temperature  and  density,  but  within  the  ordinary 
range  of  conditions  of  boiler  practice  it  is  approximately  true.  If  the 
furnace  conditions  are  constant,  so  that  the  gas  always  contains  the 
same  percentage  of  C02  and  of  0,  then  the  amount  of  fuel  burned 
in  a  given  time  is  proportional  to  the  gas  volume,  and  the  boiler 
capacity  is  also  approximately  proportional  to  it  within  moderate 
ranges  of  excess  driving.  At  very  high  rates  of  driving,  of  course, 
the  efficiency  decreases,  so  that  doubling  the  amount  of  coal  burned 
will  not  double  the  amount  of  steam  produced.  Having  once  es- 
tablished by  experiment  the  difference  of  draft  pressure  that  gives 
a  normal  rate  of  driving  of  a  given  boiler,  a  differential  pressure 
gauge  will  indicate  whether  the  boiler  is  developing  more  or  less 
than  its  rated  capacity.  Any  increase  in  the  draft  between  the  fur- 
nace and  the  damper  may,  however,  be  caused  by  something  quite 
different  from  excess  rate  of  driving,  namely,  abnormal  furnace 
conditions,  such  as  too  thin  fires  or  holes  in  the  fires.  These  con- 
ditions may  be  shown  by  a  second  gauge  indicating  the  difference 
in  pressure  between  the  ash  pit  and  the  furnace.  Having  established 
the  normal  difference  for  a  given  rate  of  driving,  a  decrease  in  that 
difference  means  decreased  resistance  of  the  fuel  bed,  which  may 
be  due  to  thin  fires  or  to  holes,  and  an  increase  in  the  difference 
means  increased  resistance  caused  by  too  thick  fires  or  fires  choked 
by  clinker  coal  or  by  caking,  or  grates  choked  by  ash  or  clinker. 

A  differential  pressure  gauge  made  by  W.  A.  Blonck  &  Co. 
of  Chicago,  111.,  takes  the  place  of  the  two  gauges  above  referred  to, 
as  illustrated  in  Fig.  227.  It  is  called  the  Blonck  efficiency  meter. 

It  consists  essentially  of  two  sensitive  draft  gauges,  the  lower 
one  filled  with  red  oil,  giving  a  relative  indication  of  the  pressure 
with  which  the  air  rushes  into  the  furnace  or  the  resistance  of  the 
fuel  bed,  while  the  upper  gauge,  filled  with  blue  oil,  gives  a  relative 
measure  of  the  amount  of  combustion  gases  passing  the  boiler  proper. 


490 


STEAM-BOILER  ECONOMY. 


In  addition  to  the  two  gauges  the  meter  is  provided  with  two 
sliding  scales,  which  are  to  be  adjusted  to  the  best  and  most  efficient 
operating  condition  of  the  particular  boiler.  The  deductions  to 
be  read  from  the  various  positions  of  the  instrument  are  shown  in 
the  diagram  below  the  illustration.  In  order  to  instruct  the  fireman 
about  the  correction  of  wasteful  conditions  in  the  fire,  the  sliding 


1,  Normal  operation  of  boiler; 


2,  Too  much  air,  fuel  bed  too  thin 

or  holes  in  fire; 

3,  Too, little  air,  fuel  bed  too  thicker 

fire  choked  by.slag; 


4,  Boiler  running-  with.overload, 


5,  Boiler_running  with  underload 


FIG.  227. DIAGRAM  OF  BLONCK  EFFICIENCY  METER  AND  PRINCIPAL  INDICA- 
TIONS OF  THE  INSTRUMENT. 

scales  are  provided  with  the  following  abbreviations:  normal  po- 
sition (arrow)  ;  excess  air  (+  air),  and  lack  of  air  (—  air).  The 
connections  between  the  instrument,  furnace  and  boiler  side  of 
damper  consist  of  standard  l/8-inch  steel  piping. 

The  Uehling  Triple  Draft  Gauge  is  shown  in  Fig.  228.  Attached  in 
front  of  the  scale  in  an  inclined  position  is  a  large  glass  tube  LL  con- 
taining a  small  tube  H  which  protudes  from  the  tube  LL  at  its  upper 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    491 


end.  H  and  L  respectively  are  in  communication  with  the  five-way 
valve  C  through  the  connections  D  and  K.  The  valve  C  is  further 
connected  through  suitable  pipes  A  with  the  ash-pit,  /  with  the 
furnace  and  G  with  gas  exit  between  the  boiler  and  the  damper.  The 
valve  C  is  operated  by  a  movable  index  J  which  revolves  in  front  of  a 
dial  upon  whch  the  letters  0,  T,  l\  B  are  shown.  When  the  index 
points  to  Oj  II  and  L  are  in  communication  and  the  gage  shows  zero. 
When  it  is  moved  to  T,  H  and  L  are  in  communication  respectively 
with  A  and  G  and  the  gage  shows  the  total  draft  between  the  ash  pit 

and  damper.  When  the  index 
is  moved  to  Ff  H  and  L  re- 
spectively communicate  with  A 
and  I  and  the  gage  shows 
furnace  draft,  i.e.,  the  drop  of 
pressure  or  resistance  through 
the  fire.  If  the  index  is  moved 


|  To  Combustion 
Chamber 


FIG.  228. — THE  UEHLING  TRIPLE  DRAFT  GAUGE.' 

to  B,  H  and  L  respectively  communicate  with  I  and  G  and  the  gage 
shows  the  boiler  draft,  i.  e.  the  drop  of  pressure  between  the  furnace 
and  the  damper. 

Flue-gas  Analysis. — The  method  of  analyzing  flue  gases  by  the 
Orsat  or  other  instruments  consists  in  measuring  a  sample,  usually 
100  cubic  centimeters,  of  filtered  gas  at  atmospheric  temperature 
and  pressure,  in  an  accurately  graduated  glass  vessel,  called  a  burette, 
which  is  kept  at  a  uniform  temperature  by  enclosing  it  in  another 
glass  vessel  filled  with  water,  then  passing  it  into  a  glass  bulb  or 
cylinder  containing  a  chemical  which  absorbs  one  of  the  constituent 
gases,  returning  it  to  the  burette,  and  measuring  it  again,  the  differ- 
ence being  the  volume  of  gas  removed  by  the  absorbent.  This  oper- 
ation is  repeated  with  different  chemicals  until  all  the  constituent 
gases  have  been  removed,  except  nitrogen  for  which  no  absorbent 
has  been  found. 


492 


STEAM-BOILER  ECONOMY. 


Steam 


The  absorbent  usually  employed  for  carbon  dioxide  is  a  concen- 
trated solution  of  caustic  potash.  For  oxygen  a  solution  is  made 
of  5  grams  of  pyrogallic  acid  in  15  c.c.  of  water  added  to  a  solution 
of  120  grams  of  caustic  potash  in  80  c.c.  of  water.  In  the  Hempel 
apparatus  slender  sticks  of  phosphorus  covered  with  water  are  some- 
times used  instead  of  the  pyrogallic  solution.  For  carbon  monoxide 
the  solution  is  made  by  dissolving  10.3  grams  of  copper  oxide  in 
100  c.c.  of  concentrated  hydrochloric  acid.  To  insure  greater  ac- 
curacy the  gas  should  be  passed  successively  through  two  bulbs  con- 
taining this  solution.  The  order  of  analysis  followed  is  always  first 
C02,  then  0,  then  CO.  The  anaylsis  for  CH4,  C2H4  and  H  is  not 
often  undertaken  in  connection  with  boiler  tests.  Gas  analysis  is  a 
delicate  operation  requiring  training  and  experience  for  accurate 
work. 

Illustrations  of  the  Orsat  and  Hempel  instruments  will  be  found 
on  pages  578  and  579. 

C02  Recorders. — A  great  variety  of  instruments  for  automatically 
analyzing  and  recording  the  percentage  of  C02  in  flue  gases  have 

been  placed  on  the  market. 
Some  of  the  earlier  ones  have 
disappeared  on  account  of 
their  complexity  and  the  dif- 
ficulty of  keeping  them  in 
good  wrorking  order.  C02 
recorders  are  now  (1914)  ad- 
vertised by  Precision  Instru- 
ment Co.,  Detroit,  Mich.; 
Uehling  Instrument  Co.,  Pas- 
saic,  N".  J.,  and  Cambridge 
Scientific  Instrument  Co., 
Cambridge,  England. 

The  principle  of  the  Ueh- 
ling instrument  is  shown  in 
diagrammatic  form  in  Figs. 
229  and  230.  Referring  to 

Fig  229,  the  gas  to  be  analyzed  is  drawn  through  two  apertures,  A  and 
B,  by  a  constant  suction  produced  by  an  aspirator.  If  the  apertures 
are  kept  at  the  same  temperature,  the  suction  or  partial  vacuum  in  the 
chamber  between  the  two  apertures  will  remain  constant  so  long  as  the 
gas  passes  through  both  apertures ;  if,  however,  part  of  the  gas  be  taken 


SJ 


*    Gas  lalcft 


—205* 


-- 


FIG.  229. — PRINCIPLE  OF  THE  UEHLING 
PYROMETER  AND  CO2  APPARATUS. 


BOILER  ATTACHMENTS  AND  BOILER-ROOM   APPLIANCES.    493 


away  or  absorbed  in  the  space  between  the  two  apertures,  the 
vacuum  will  increase  in  proportion  to  the  amount  of  gas  absorbed. 
It  is  evident  that  if  a  manometer  or  light  vacuum  gauge  be  connected 
with  this  chamber,  the  amount  of  gas  absorbed  will  be  indicated  by 
the  vacuum  reading. 

The  diagram  of  Fig.  230  shows  the  more  important  parts  of  the 
complete  instrument,  showing  the  path  of  the  gases  through  the 
filter,  apertures  and  absorp- 
tion chamber.  The  instru- 
ment consists  primarily  of 
a  filter,  absorption  chamber, 
two  apertures  (A  and  B) 
and  a  small  steam  aspirator. 
Gas  is  drawn  from  the 
boiler  by  means  of  the  as- 
pirator through  a  prelimi- 
nary filter  located  at  the 
boiler,  and  then  through 
other  filters  on  the  instru- 
ment, which  insure  that  the 
gas  flowing  through  the 
apparatus  is  absolutely  clean 
and  eliminate  any  possible 
clogging.  The  clean  gas 
passes  through  aperture  A, 
thence  through  the  absorp- 
tion chamber  and  aperture 


To  Boiler  Room  Indicator 


To  Recording  Gauge 


Caustic  Drip 


bsorption  Chamber 


Gas  Inlet 


Caustic  Overflow 


FIG.  230. — DIAGRAM  OF  THE  UEHLCISG 
CO2  RECORDER. 


B,  to  the  aspirator. 

A     dilute     solution     of 
caustic  soda  flows  into  the 

absorption  chamber  by  gravity  from  a  tank,  through  a  sight-feed  which 
is  regulated  by  a  cock  as  shown.  The  C02  is  completely  absorbed  by 
the  caustic .  solution  as  the  gas  flows  through  the  absorption  chamber 
and  while  it  is  between  apertures  A  and  B  (in  recent  modifications  of 
the  instrument  the  solution  is  replaced  by  a  solid  absorbent).  This 
reduces  the  volume  and  causes  a  change  in  the  tension  (partial 
vacuum)  of  the  gas  between  the  two  apertures.  This  tension  varies 
in  exact  accordance  with  the  percentage  of  C02  contained  in  the 
gas,  and  is  indicated  by  a  water  column  at  the  instrument,  which 
is  calibrated  so  as  to  indicate  directly  percentages  of  C02.  This 


494 


STEAM-BOILER  ECONOMY. 


partial  vacuum,  or  per  cent  C02,  is  also  communicated  to  an  indi- 
cating gauge  in  front  of  the  boiler  and  to  a  recording  gauge  which 
may  be  located  at  a  considerable  distance  from  the  machine.  Fig.  231 
is  a  reproduction  of  a  tape  record  from  a  recording  gauge.  Circular 
gauge  records  may  also  be  used.  The  lowest  portion  of  the  record 
shows  when  the  firing  doors  were  opened  for  cleaning  fires,  and  the 
serrations  in  the  remainder  of  the  record  show  the  variable  con- 
ditions in  the  furnace  as  the  coal  burned  down  and  fresh  coal  was 
added. 

The  TIehling  Pyrometer. — The  principle  of  the   C02  apparatus 
above  described  is  also  applied  in  the  Uehling  pyrometer.     The  aper- 


Uehling  Instrument  Co 

N       1PM     2PM     3PM     4PM 


FIG.  231.— RECORD  OF  A  C02  APPARATUS. 

ture  A  is  located  in  a  nickel  tube  which  is  exposed  to  the  heat  to 
be  measured,  while  the  aperture  B  is  kept  at  a  lower  temperature, 
usually  by  enclosing  it  in  a  chamber  surrounded  by  exhaust  steam 
at  atmospheric  pressure.  The  suction  at  the  aspirator  being  con- 
stant, the  partial  vacuum  at  C  will  depend  on  the  difference  of 
temperatures  at  A  and  B,  and  this  vacuum  is  indicated  on  a  water 
gauge  and  also  on  a  recording  gauge  as  in  the  C02  apparatus,  the 
graduations  being  made  to  record  temperatures  directly. 

A  pyrometer  and  C02  apparatus  are  also  combined  in  one  machine. 

Piping  Connections  for  C02  Recorders. — Fig.  232  shows  a  plan  of 
the  piping  from  eight  boilers  to  a  C02  recorder.  A  %-in.  pipe  runs 
from  the  middle  of  the  last  pass  in  each  boiler  to  a  header  that  is 
located  at  the  center  of  the  system,  and  is  easily  accessible.  The 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    495 


header  then  runs  to  the  recorder,  which  is  placed  in  front  of  the 
boilers  where  the  minimum  amount  of  piping  possible  will  reach 
it,  and  in  a  cool,  light  place  where  it  can  be  easily  watched.  The 


Test  Lines 


,Header  to  Recorder 


' 

/ 

\ 

/ 

/ 

It 

' 

It 

\  n 

fc 

-&+ 

«-a- 

t+-<a- 

1  V, 

iaiL 


FIG.  233. — PIPE  FOR  SAMPLING  FLUE  GASES. 


xSteam 

FIG.  232. — PIPING  FOR  CC>2  RECORDERS. 

header,  near  the  recorder,  contains  a  filter  to  remove  soot,  and  it  is 
also  provided  with  a  steam    (or   compressed  air)    connection,   used 
to    blow    deposits    of    soot 
from  the  pipes,  and  at  the 
lowest   point   with   a   drain 
pipe     and     valve,     through 
which  the  water  of  conden- 
sation may  be  drained  out. 

Fig.  233  shows  a  samp- 
ling pipe  for  collecting 
gases  for  analysis  or  for 

C02  recorders.     From  16  to  20  %-inch  holes  are  drilled  in  a  %-inch 
pipe  which  is  closed  at  the  end. 

A  more  accurate  apparatus  for  collecting  samples  of  flue  gases, 
designed  by  J.  C.  Hoadley  about  1885,  is  shown  in  Fig.  255.  Adjoin- 
ing the  flue  there  is  placed  a  shallow  air-tight  sheet-iron  box,  and 
numerous  14-inch  pipes  of  equal  length  are  placed  as  shown  in  the 
illustration,  so  as  to  collect  gas  from  different  parts  of  the  cross- 
section  of  the  flue,  and  deliver  them  to  the  box,  where  they  are 
mixed  before  being  carried  to  the  analyzing  apparatus. 

The  Nassau  C02  Machine.— Fig.  234  shows  a  C02  machine  designed 
by  F.  F.  Uehling.  It  is  made  up  in  a  light  cast  aluminum  case,  the 
size  of  which  is  3x4x12  inches.  The  burette  A  is  surrounded  by  the 
jacket  E,  which  contains  a  solution  of  acidulated  methyl  orange  and 
communicates  with  A  at  the  bottom.  By  blowing  into  the  top  of  E 
by  means  of  a  mouthpiece  W,  through  tube  G,  the  liquid  will  be 
forced  into  the  burette  A.  When  A  is  full,  the  three-way  cock  H 


496 


STEAM-BOILER  ECONOMY. 


FIG.  234.— CO2  APPARA- 
TUS. 


is  closed  to  A,  to  prevent  the  liquid  returning  to  E.  By  actuating 
pump  P,  gas  will  be  drawn  from  the  boiler  or  flue  into  the  tube  D, 
through  the  inlet  7.  When  the  gas  reaches  D,  H  is  opened  so  as 
to  connect  the  source  of  the  gas  with  the 
absorption  chamber  B  through  a  capillary 
tube  C.  B  is  the  short  leg  of  a  U-tube  and  is 
filled  with  a  caustic  solution  and  fine  iron 
wire  to  provide  ample  surface  for  quick 
absorption.  When  B  is  connected  with  the 
source  of  gas  through  H,  the  absorbent  will 
rise  in  C  to  a  certain  level,  depending  upon 
the  tension  of  the  gas  in  D.  The  movable 
index  X  is  then  shifted  to  coincide  with  this 
level.  Cock  //  is  then  turned  so  as  to  con- 
nect D  with  A,  and  by  means  of  the  mouth- 
piece W,  the  gas  is  drawn  from  D  into  A 
until  the  level  of  the  liquid  in  A  coincides 
with  the  zero  line  of  the  scale.  The  burette 
then  contains  100  volumes  of  the  gas.  Now  by  turning  the  cock  H 
so  as  to  connect  A  with  B,  opening  the  pinchcock  TT'and  blowing 
through  W,  the  gas  will  be  forced  into  B,  where  in  less  than  30 
seconds  the  CO2  in  the  gas  will  be  entirely  absorbed.  The  remaining 
gas  is  then  drawn  back  into  A  until  the  level  of  the  solution  in  B 
again  reaches  the  index  X.  The  pinchcock  K  is  then  closed  and  the 
level  of  the  liquid  in  A  will  indicate  the  per  cent  of  C02  absorbed. 

The  Si-meter  C02  Recorder. — This  instrument  is  made  by  the 
Cambridge  Scientific  Instrument  Co.,  Ltd.,  Cambridge,  England. 
Fig.  235  is  a  diagrammatic  sketch  of  the  internal  construction.  The 
apparatus  consists  of  two  gas  meters  M x  and  M.2,  an  absorption  box  E, 
a  water  suction  pump  B,  and  a  recording  mechanism  F,  G. 

The  water- jet  suction  pump  or  aspirator  B}  with  the  consumption 
of  about  6  gallons  per  hour,  draws  about  l1/^  cubic  feet  of  the  flue 
gas  through  the  instrument  per  hour.  The  gas,  entering  the  recorder 
at  D,  after  having  first  passed  through  the  soot  filter,  is  cooled  in 
the  first  chamber  of  the  cooler  K,  and  is  then  measured  in  meter  Mlf 
The  C02  is  then  extracted  from  the  gas  in  the  absorption  chamber 
E  containing  lime;  and,  since  during  this  chemical  process  the  re- 
mainder of  the  gas  becomes  heated,  it  is  again  cooled  to  its  former 
temperature  by  being  passed  through  a  second  chamber  of  the  cooler 
K.  From  the  cooler  the  gas  is  led  to  the  second  meter  M2  to  be 


BOILER  ATTACHMENTS  AND  BOILER-ROOM  APPLIANCES.    497 

again  measured,  and  is  then  allowed  to  escape  into  the  atmosphere 
by  way  of  the  aspirator  B  and  the  water  vessel  C. 

The  water  which  is  employed  for  the  working  of  the  instrument 
enters  at  inlet  A,  and  flows  through  the  cooler  K  into  the  aspirator 
B.  It  there  draws  in  the  flue  gas,  and  the  mixture  of  water  and  gas 
passes  into  the  water  vessel  C.  From  this  the  water  escapes  through 
an  overflow  drain  pipe  H,  and  the  gas  bubbles  into  the  atmosphere. 

The  two  gas  meters  are  partially  filled  with  oil,  and  are  so  ar- 
ranged that,  when  no  absorption  takes  place,  the  meter  M 2  runs  about 
4  per  cent  slower  than  the  meter  M^.  Thus  when  no  C02  is  ab- 


Aspirator 

Drawing  Flue  Oas 

through  Meters 


Outlet  Gas 
Water  to  Drain 


FIG.  235. — DIAGRAM  OF  THE  BI-METER  CO2  RECORDER. 

sorbed  the  pen  is  made  to  record  lines  about  3  or  4  mm.  in  height, 
and  adjustment  must  be  made  so  that  the  upper  ends  of  these  "zero" 
marks  should  lie  on  the  zero  line  of  the  chart.  When  this  is  secured, 
the  apparatus,  on  connecting  up  the  absorption  chamber  in  position, 
records  the  percentage  of  C02  contained  in  the  gases  which  are  under 
test. 

The  recording  pen  is  actuated  by  means  of  a  differential  drive  F, 
operated  by  meters  M x  and  M2.  On  an  average  from  20  to  25  analyses 
may  be  recorded  per  hour,  the  number  being  dependent  upon  the 
volume  of  the  flue  gases  pasing  through  the  instrument.  This  num- 
ber may  be  reduced  by  adjustment  of  a  cock  P  placed  in  the  gas 
passage  near  the  aspirator  B. 

Oxygen  Recorder. — An  oxygen  recorder  would  be  even  more  useful 


498 


STEAM-BOILER  ECONOMY. 


than  a  C02  recorder,  but  at  this  date  (1914)  no  such  instrument  is 
on  the  market.  The  author  has  suggested  that  the  bi-meter  recorder 
could  be  used  for  this  purpose,  using  phosphorus  as  the  absorbent. 

Superheating  of  Steam. — The  use  of  superheated  steam  at  a  tem- 
perature of  about  500°  F.  has  become  almost  universal  in  large  power 
plants  since  the  introduction  of  the  steam  turbine.  In  addition  to 
the  lessening  of  the  steam  consumption,  the  use  of  superheated  steam 
increases  the  life  of  the  buckets  of  the  turbine  by  avoiding  the  erosion 
which  is  due  to  water  in  the  steam.  In  regard  to  the  saving  of  steam 
due  tt)  superheating,  the  following  figures  are  given  in  a  catalogue 
of  Power  Specialty  Co.,  makers  of  the  Foster  superheater. 

A  3300  H.P.  Lenz  cross-compound  engine  having  371/2-in.  and 
63-in.  diameter  cylinders,  55-in.  stroke,  at  Charlottenburg,  Ger- 
many, with  192  Ibs.  gauge  pressure,  26-in.  vacuum,  107  revs,  per 
min.,  gave  the  following  steam  consumption : 


Temp, 
of 

Sperheat. 

Load  

1/4 

1/2 

3/4 

1/1 

5/4 

Steam. 

570° 
660° 

185°  F. 
275  °F. 

Steam  per  I.  H.P.  hr.,  Ibs  
Steam  per  I.  H.P.  hr  ,  Ibs.  .  .  . 

11.1 
10  6 

10.1 
9.7 

9.5 
9.0 

9.2 

8  8 

9.7 
9.2 

The  saving  in  steam  effected  by  superheating  100°,  as  compared 
with  saturated  steam,  is,  approximately,  for  steam  turbines,  10  per 
cent;  triple-expansion  engines,  12  per  cent;  compound  engines,  14 
per  cent;  simple  engines,  18  per  cent  and  over. 

Tests  of  Buckeye  engines,  simple,  12xl6-in.,  and  compound  10 
and  17 1/2x1 6-in.,  with  steam  at  100  to  110  Ibs.  pressure,  gave  the 
following : 


Engine. 

Per  cent 
of  Rated 
Load. 

Degrees  of  Superheat. 

0 

50 

100 

150 

200 

Lbs.  Steam  per  I.  H.P.  Hr. 

Simple,  non-condensing  

30 
50 

100 
100 
100 

35 
31.5 

28.5 

18 

28 
25.5 
24.0 

16.5 

24 
22 
20 
17.5 
14 

21.5 
19 
18 
15.5 
12.5 

19.5 
17.5 
17.5 
14.6 
11.5 

Simple,  non-condensing  
Simple,  non-condensing  

Compound,  non-condensing  
Compound,  condensing  

BOILER  ATTACHMENTS  AND  BOILER-ROOM   APPLIANCES.    499 

The  Foster  Superheater. — This  superheater  consists  of  a  series 
of  straight  seamless  drawn  steel  tubes,  expanded  at  one  end  into 
steel  manifolds  or  connecting  headers,  and  at  the  other  end  into 
return  headers,  or  return  bends.  One  element,  with  a  return  bend, 
is  shown  in  Fig.  236.  On  the  outside  of  each  tube  is  fitted  a  series 
of  cast-iron  annular  gills  or  flanges,  bored  to  gauge  and  shrunk  on 
to  the  tube  so  as  to  be  practically  integral  with  it,  at  the  same  time 
exposing  an  external  surface  of  cast  iron,  which  metal  is  best  adapted 
to  resist  the  action  of  the  heated  gases.  The  .mass  of  metal  in  the 
tubes  and  covering  acts  as  a  reservoir  for  heat,  which  is  imparted  to 


FIG.  236. — RETURN  BEND  ELEMENT  AND  CONNECTING  HEADERS  OF  A  FOSTER 

SUPERHEATER. 

the  steam  evenly,  tending  to  secure  a  constant  temperature  of  steam 
in  spite  of  fluctuations  in  the  temperature  of  the  hot  gases.  Inside 
of  the  elements  there  are  placed  other  tubes  of  wrought  iron,  which 
are  centrally  supported  by  means  of  knobs  or  buttons  regularly  spaced 
throughout  their  length.  These  inner  tubes  are  closed  at  the  ends. 
A  thin  annular  passage  for  the  steam  is  thus  formed  between  the 
inner  and  outer  tubes. 

The  superheater  is  designed  with  a  view  to  avoiding  the  necessity 
for  flooding  devices  or  any  form  of  connection  between  the  water 
space  of  the  boiler  and  the  superheater.  The  protection  afforded 
by  the  external  covering  of  cast  iron  is  ample  to  prevent  damage 
to  the  surface  during  the  process  of  steam  raising. 


CHAPTER  XV. 
BOILER  TROUBLES  AND  BOILER  USERS'  COMPLAINTS. 

IT  is  the  experience  of  every  large  boiler-making  concern  that  of 
all  the  boilers  it  sells,  a  certain  proportion  are,  shortly  after  erection, 
complained  of  by  the  purchaser  as  being  unsatisfactory.  When  such 
complaints  are  received,  an  expert  in  boiler-testing  and  management 
is  usually  sent  to  make  an  investigation,  and,  if  possible,  to  remedy 
the  trouble.  In  most  cases  he  succeeds,  after  a  great  deal  of  difficulty, 
in  satisfying  the  purchaser,  either  by  improving  the  conditions  of 
the  running  of  the  boiler  or  by  showing  that  the  boiler  is  not  to 
blame  for  the  trouble;  but  sometimes  he  fails,  and  the  matter  is 
finally  adjusted  by  the  boiler  being  taken  out,  by  a  reduction  in  the 
price,  or  by  recourse  to  arbitration,  or  to  a  law-suit.  In  a  law-suit 
the  boiler-maker  usually  wins,  for  the  reason  that  a  boiler-maker, 
having  had  previous  experience  in  such  matters,  is  not  apt  to  go  to 
law  unless  he  has  a  very  strong  case.  The  purchaser,  of  course,  also 
thinks  he  has  a  strong  case,  but  he  is  apt  to  be  not  well  posted  on 
the  law  of  contracts,  and  his  attorney  is  apt  to  be  ignorant  of  the 
amount  of  evidence  which  the  boiler-maker  will  bring  forward  on  the 
trial,  and  therefore  underrates  the  strength  of  the  boiler-maker's  side 
of  the  case.  It  is  the  object  of  this  chapter  to  discuss,  not  the  troubles 
and  complaints  concerning  boilers  in  their  relation  to  possible  law- 
suits, but  those  that  may  be  avoided  or  remedied  by  good  engin- 
eering. 

The  complaints  from  boiler-users  concerning  new  boilers  may  be 
divided  into  three  general  classes :  1,  Low  capacity ;  2,  Structural 
defects,  such  as  leaks,  burnt  tubes  and  plates,  etc. ;  3,  Poor  economy. 
The  last  is  not  often  a  cause  of  complaint,  because  the  great  majority 
of  boiler-users  make  no  tests  to  determine  economy,  and  therefore  if 
their  boilers  should  be  deficient  in  economy,  they  are  ignorant  of  it. 
But  if  a  boiler  does  not  give  the  amount  of  steam  that  is  needed  from 
it,  or  if  it  leaks,  the  trouble  is  apparent  at  once  and  complaint  is 
made  immediately. 

500 


BOILER   TROUBLES   AND  BOILER   USERS'   COMPLAINTS.    501 

The  most  common  causes  of  complaints  and  troubles  are  the 
following : 

1.  Poor  draft. 

2.  Insufficient  grate  surface. 

3.  Poor  coal. 

4.  Furnace  not  adapted  to  kind  of  coal. 

5.  Bad  setting  of  boiler. 

6.  Leaks  of  air  through  brick- work. 

7.  Improper  tiring. 

8.  Insufficient  heating  surface   (boiler  too  small). 

9.  Bad  water. 

We  will  now  discuss  these  causes  of  trouble,  and  their  remedies, 
in  the  order  named. 

Poor  Draft. — This  is  a  relative  term;  what  is  poor  draft  for  one 
set  of  conditions  is  ample  draft  for  another.  The  proper  force  of 
draft  for  a  given  case,  measured  at  a  point  between  the  damper  in  the 
flue  and  the  boiler  itself,  may  be  as  low  as  14  inch  of  water-column, 
and  in  another  case  over  1  inch  may  be  required,  depending  on  the 
type  of  boiler,  on  the  area  and  the  course  of  the  draft-passage  through 
the  boiler,  on  the  area  of  grate  surface,  on  the  style  of  grate-bars, 
and  on  the  kind  of  coal.  The  immediate  effect  of  poor  draft  is 
insufficient  coal-burning  capacity.  The  first  test  to  be  applied  to 
discover  whether  or  not  the  draft  is  insufficient  is  to  weigh  the  coal 
burned  in  each  hour  during  the  period  between  two  cleanings  of  the 
grates,  and  to  compare  the  amounts  burned  each  hour  with  the  amount 
which  a  calculation  shows  should  be  burned  to  evaporate  the  desired 
amount  of  water.  Thus,  suppose  that  it  is  expected  that  the  boiler 
should  evaporate  3500  Ibs.  of  water  per  hour,  and  the  temperature  of 
feed-water,  the  steam-pressure,  and  the  quality  of  coal  are  such  that 
7  Ibs.  of  water  should  be  evaporated  per  pound  of  coal,  then  the  coal- 
burning  capacity  should  be  not  less  than  500  Ibs.  during  each  hour 
between  cleanings.  If  200  Ibs.  is  used  in  the  first  part  of  the  test  to 
build  up  the  fire,  and  an  equal  amount  is  burned  down  at  the  close  of 
the  test,  in  order  to  have  a  thin  bed  of  coal  for  cleaning,  then  a  five- 
hours^  record  of  coal  fed  between  cleanings  should  show  approxi- 
mately 700,  500,  500,  500,  and  300  Ibs.  If  the  record  gave  600,  400, 
400,  400,  and  200  Ibs.  it  would  indicate  insufficient  draft  for  the  kind 
of  grate  and  the  kind  of  coal.  If,  however,  it  should  show  700,  500, 
400,  300,  200  Ibs.,  it  would  indicate  that  the  draft  itself  was  ample, 
but  that  the  grates  were  being  gradually  choked  by  ashes  and  clinkers. 


502  STEAM-BOILER  ECONOMY. 

In  the  second  case,  in  which  the  coal  is  burned  steadily  at  the  rate 
of  400  Ibs.  of  coal  per  hour,  when  500  Ibs.  is  required,  the  remedy 
indicated  is  an  increase  of  the  draft.  It  will  often  happen  that  such 
remedy  can  easily  be  given  by  a  slight  change  in  the  flue-connection 
between  the  boiler  and  chimney.  Right-angled  bends  in  this  flue- 
connection  are  exceedingly  common,  and  they  frequently  cut  down 
the  force  of  draft  at  the  boiler  to  one-half  of  that  in  the  chimney. 
Whenever  possible  they  should  be  changed  to  long  easy  curves.  When 
two  or  more  adjoining  boilers  deliver  their  gases  into  one  horizontal 
flue,  the  area  of  this  flue  should  increase  as  it  travels  from  the  most 
distant  boiler  to  the  chimney,  the  connection  from  each  boiler  to  the 
flue  should  be  a  curved  one,  and  the  flue  itself  should  enter  the 
chimney  with  an  ascending  curve.  Before  making  the  changes  here 
suggested,  the  existing  draft  in  the  chimney,  at  various  points  in  the 
flue,  and  at  each  boiler,  should  be  tested  by  a  U-tube  draft-gage. 
If  there  are  no  defects  in  the  flue-connection,  the  next  remedy  to  be 
applied  is  an  increase  in  the  height  of  the  chimney.  If  this  is  not 
feasible,  and  a  reference  to  a  table  of  proportions  of  chimneys  shows 
that  the  chimney  has  not  sufficient  area  for  the  amount  of  coal  to  be 
burned,  then  a  new  chimney  with  larger  area  is  required.  In  case 
it  appears  that  the  chimney  is  of  sufficient  area  and  its  height  cannot 
be  increased,  a  remedy  may  be  found  in  enlarging  the  area  of  grate- 
surface  or  in  using  a  different  kind  of  coal. 

If  the  test  of  the  coal-burning  capacity  shows  a  decreasing  rate  of 
burning,  such  as  700,  500,  400,  300,  and  200  Ibs.  per  hour,  indicating 
a  gradual  choking  of  the  grate  by  clinker,  the  most  obvious  remedy  is 
the  use  of  a  shaking-grate,  by  which  the  accumulation  of  ashes  and 
clinker  may  be  prevented.  Such  a  grate  will  sometimes  increase  the 
capacity  of  a  boiler  as  much  as  30  per  cent,  although  its  use  may 
entail  a  loss  of  economy  of  2  or  3  per  cent  due  to  the  coal  shaken 
into  the  ash-pit  with  the  ashes.  A  change  of  coal  from  a  clinker- 
ing  to  a  non-clinker  ing  variety  will  sometimes  prove  a  sufficient 
remedy. 

With  a  clinkering  coal,  increase  of  draft  is  sometimes  of  no  benefit 
in  increasing  the  capacity  of  a  boiler,  but  rather  the  reverse ;  for  when 
the  fire  is  freshly  cleaned,  a  strong  draft  with  such  coal  causes  at  first 
a  rapid  combustion,  resulting  in  high  temperature  and  a  fusing  of 
the  clinker,  which  soon  obstructs  the  passage  of  air  through  the 
grates,  checking  the  combustion.  Enlargement  of  the  grate  surface 
and  a  slower  rate  of  combustion  per  square  foot  of  grate  are  then  the 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.      503 

proper  remedies,  and  if  these  are  impracticable,  then  shaking-grates 
should  be  used.  The  tendency  to  form  clinker  may  sometimes  be 
lessened  by  blowing  a  little  steam  under  the  grate-bars,,  or  by  letting 
a  little  water  run  into  the  ash-pit.  The  evaporation  of  the  water  helps 
to  cool  the  grate-bars. 

When  the  grate-surface  and  the  draft  are  adapted  to  the  kind  of 
coal  that  is  being  used,  but  it  is  desirable  to  use  a  poorer  grade  of 
coal  on  account  of  its  low  price,  and  the  available  draft  pressure  is 
insufficient  to  burn  this  coal  at  the  required  rate,  the  remedy  is 
either  to  enlarge  the  grate  surface  or  to  use  forced  draft,  or  both. 

Insufficient  Grate  Surface,  and  Poor  Coal. — These  two  causes  of 
trouble  may  be  considered  together,  as  they  are  co-related.  Insufficient 
grate  surface  for  one  grade  of  coal  may  be  ample  -for  another  grade. 
By  grade  of  coal  here  is  meant  its  quality  as  regards  amount  of  ash 
and  kind  of  ash.  If  the  percentage  of  ash  in  the  coal  is  low,  and  it  is 
low  in  iron  and  sulphur,  which  are  the  principal  causes  of  clinker,  a 
relatively  small  grate  surface  and  a  strong  draft  may  be  used,  such, 
for  instance,  as  to  cause  the  burning  of  as  much  as  20  Ibs  of  anthra- 
cite, 25  or  30  Ibs.  of  semi-bituminous,  and  30  to  40  Ibs.  of  bituminous 
coal  per  square  foot  of  grate  per  hour;  but  if  the  ash  is  excessive,  or 
if  it  forms  clinker,  then  a  large  grate  is  needed,  so  that  these  rates 
of  combustion  may  be  reduced  30  to  50  per  cent. 

Furnace  Not  Adapted  to  Coal. — Forty  or  fifty  years  ago  it  used  to 
be  the  custom  to  set  boilers  with  the  grate-bars  near  to  the  shell  of 
the  boiler,  12  to  15  ins.  being  a  common  distance,  the  idea  being  that 
there  was  a  loss  of  radiant  heat  if  the  boiler  was  removed  a  greater 
distance  from  the  grate.  The  idea  was  erroneous,  as  may  be  Learned 
by  considering  the  question  "If  the  heat  is  lost,  where  does  it  go?" 
A  pound  of  coal,  in  burning  under  a  boiler,  generates  so  many  heat- 
units.  A  small  fraction  of  them  is  lost  through  the  side  walls  of  the 
furnace.  The  heat  radiated  into  the  side  walls  is  radiated  back  again 
to  the  fire,  to  the  heating  surface  of  the  boiler,  to  the  particles  of 
carbon  in  the  flame,,  and  to  gaseous  products  of  combustion,  and  it 
finally  all  gets  into  the  boiler  except  that  which  is  carried  out  of  the 
chimney  or  through  the  walls  of  the  setting.  With  dry  anthracite 
coal,  which  burns  practically  without  flame,  almost  any  kind  of  furnace 
is  a  good  one,  but  a  furnace  in  which  the  grate  is  12  or  15  ins.  from 
the  boiler  is  entirely  unsuited  to  the  burning  of  bituminous  coal.  A 
distance  of  from  3  to  4  feet  from  the  grate  to  the  boiler  is  now,  com- 
mon practice  for  bituminous  coal.  With  very  smoky  coal,  5  feet  is 


504  STEAM-BOILER  ECONOMY. 

sometimes  used;  and  6  or  8  feet  would  be  better.*  With  lignite,  wet 
refuse  lumber,  tan-bark,  bagasse,  etc.,  10  feet  or  more  may  be  used 
with  advantage. 

A  furnace  for  a  steam-boiler  is  not  adapted  to  the  coal  whenever 
the  flame  from  the  coal  is  extinguished  by  the  comparatively  cool 
surfaces  of  the  boiler,  and  whenever  it  is  not  possible  by  skilful 
operation  of  the  furnace  to  prevent  smoke  escaping  from  the  chimney. 
A  smoky  chimney  is  proof  either  of  an  improper  furnace  for  the  kind 
of  coal  or  of  unskilful  firing,  or  both;  usually  of  the  former.  - 

The  loss  of  economy  and  the  diminution  of  capacity  of  steam- 
boilers  due  to  smoky  chimneys  is  usually  under-estimated.  It  is 
stated  that  it  has  been  found  by  experiment  that  the  amount  of  soot 
actually  present  in-  smoke  is  less  than  one  per  cent  of  the  weight  of 
coal  burned.  Numerous  experiments  have  shown  also  that  when 
"smoke-consumers"  are  applied  to  a  steam-boiler,  while  the  smoke 
may  be  prevented,  no  gain  in  economy  follows.  This  may  be  quite 
true,  but  the  "smoke-consumers"  referred  to  usually  effect  the  smoke-- 
prevention by  means  of  an  excessive  supply  of  air,  which  involves 
waste  of  fuel,  so  that  the  failure  to  show  a  gain  in  economy  is  due 
to  substituting  the  waste  due  to  excessive  air-supply  for  the  waste  due 
to  imperfect  combustion. 

While  it  may  be  true  also  that  the  soot  in  smoke  represents  only 
one  per  cent  of  the  fuel  burned,  this  is  not  the  only  loss  of  fuel  which 
attends  the  smoky  chimney,  for  the  smoke  not  only  contains  soot,  but 
it  may  also  contain  invisible  hydrocarbon  gases  distilled  from  the  coal, 
and  carbon  monoxide  produced  in  the  furnace  by  imperfect  combus- 
tion of  the  carbon. 

Bad  Setting  of  Boiler. — If  the  type  of  setting  is  one  adapted  to  the 
kind  of  coal,  it  may  still  have  errors  of  design  or  of  construction  which 
may  lead  to  the  loss  of  economy  or  of  capacity,  or  of  both.  Examples 
of  such  errors  are:  (1)  Boiler  set  too  close  to  the  grate.  (2)  Insuffi- 
cient area  through  the  flues,  damper,  or  other  passages  for  the  gas.  (3) 
Excessive  area  of  gas-passages,  so  placed  that  the  gases  can  find  a  path 
of  least  resistance  along  or  across  the  heating  surfaces,  and  thus  be 
"short-circuited."  The  error  of  the  boiler  being  set  too  close  to  the 
grate  has  already  been  discussed.  Insufficient  area  of  gas  passages 

*  In  the  most  recent  practice  these  figures  are  often  greatly  increased.  As 
much  as  14  feet  has  been  used  with  the  Babcock  &  Wilcox  type  of  boiler,  and 
with  the  Stirling  type  as  much  as  28  feet  from  the  level  of  the  grate  to  the  point 
where  the  gases  flow  into  the  bank  of  tubes  near  their  upper  end. 


BOILER   TROUBLES  AND  BOILER   USERS1   COMPLAINTS,    505 

acts  to  choke  the  draft  and  restrict  the  coal-burning  capacity,  just  as 
do  insufficient  chimney  area  or  height,  and  insufficient  grate  area. 
Whether  or  not  the  gas-passages  are  insufficient  in  area  can  usually  be 
determined  by  inspection  and  comparison  of  their  measurements  with 
that  of  the  chimney  and  grate.  A  draft-gage  should  be  applied  at 
different  points  in  the  gas-passages,  between  the  chimney  and  the 
furnace,  in  order  to  find  whether  there  is  any  serious  choke  in  the  draft. 
This  should  be  done  when  the  fire  is  clean  and  burning  brightly. 

Whether  or  not. the  areas  of  the  gas-passages  are  too  large,  or  such 
as  to  allow  of  short-circuiting  of  the  gases,  is  usually  a  rather  difficult 
matter  to  determine.  The  error  may  be  suspected  to  exist  whenever 
it  is  found  by  an  evaporation-test  that  the  boiler  gives  a  lower  result 
than  should  be  expected  under  the  conditions,  and  at  the  same  time 
there  is  found  a  high  temperature  of  the  chimney-gases  and  a  low  rate 
of  evaporation  per  square  foot  of  heating  surface.  This  same  set  of 
combined  conditions,  viz.,  low  capacity,  low  economy,  and  high  tem- 
perature of  chimney-gases,  may,  however,  be  the  result  of  imperfect 
combustion  in  the  furnace  and  burning  of  the  gases  in  the  gas-passages 
between  the  furnace  and  the  chimney.  If  there  is  no  evidence  of 
imperfect  furnace-conditions  and  of  the  burning  of  gas  in  the  passages, 
then  short-circuiting  of  the  gases  is  probably  the  cause  of  the  observed 
results.  After  making  the  diagnosis  of  short-circuiting,  another  test 
of  the  boiler  should  be  made,  if  sufficient  draft  is  available,  at  a  very 
much  higher  rate  of  combustion.  If  it  is  found  that  this  test  gives 
an  increase  of  economy  with  no  increase  in  the  temperature  of  the 
chimney-gases,  this  would  tend  to  prove  that  short-circuiting  existed 
during  the  first  test.  The  gases  may  short-circuit  citing  the  test  at 
a  low  rate  of  driving  and  not  during  the  other  test,  because  in  the 
first  test  the  volume  of  gases  is  relatively  small,  and  in  the  second  it 
is  large,  so  that  they  completely  fill  the  passages.  The  gas-passages 
may,  therefore,  be  properly  proportioned  for  a  high  rate  of  driving, 
but  may  be  too  large  for  a  low  rate. 

Another  kind  of  test  which  may  be  applied  to  determine  whether 
or  not  there  is  short-circuiting  of  the  gases,  is  the  exploration  of 
various  portions  of  the  gas-passage  by  an  electric  pyrometer,  in  order 
to  discover  if  any  portion  is  not  swept  by  the  current  of  hot  gas. 
It  is  highly  probable  that  many  of  the  very  low  economic  results 
sometimes  obtained  in  boiler-tests,  which  are  unexplained  by  the 
observed  conditions,  are  due  to  this  short-circuiting,  the  existence 
of  which  may  be  revealed  by  the  electric  pyrometer. 


506  STEAM-BOILER  ECONOMY. 

When  the  short-circuiting  of  the  gases  is  proved,  the  remedy  is 
obviously  to  change  the  areas  of  the  gas-passages,  or  to  place  baffle- 
plates  or  retarders  in  them,  so  as  to  partially  obstruct  those  portions 
of  the  passages  where  the  gases  tend  to  travel  with  the  greatest  velocity, 
and  compel  them  to  travel  at  a  uniform  rate  across  or  along  the  whole 
extent  of  heating  surface. 

Leaks  of  Air  through  Brickwork. — If  there  are  any  large  air-leaks 
through  the  brickwork,  they  can  usually  be  discovered  by  inspection. 
There  are  two  methods  of  making  examinations  for  small  leaks;  first 
passing  the  flame  of  a  candle  over  all  the  joints  of  the  brick-work  and 
noting  where  it  is  drawn  inwards  by  the  draft;  second,  firing  a  few 
shovelsful  of  smoky  coal  while  the  damper  is  shut.  The  smoke  will 
then  be  driven  out  through  any  crevices  that  may  exist.  The  exist- 
ence of  air-leaks  in  the  brick-work  beyond  the  furnace  may  be  inferred 
from  the  results  of  a  boiler-test,  if  these  results  show  low  economy 
together  with  low  temperature  of  the  chimney-gases  and  apparently 
good  furnace-conditions,  insuring  complete  combustion.  If  the  coal 
is  thoroughly  burned  in  the  furnace,  then  low  economy  is  usually  ac- 
companied with  high  temperature  of  the  chimney-gases,  caused  either 
by  insufficient  extent  of  heating  surface  or  by  short-circuiting  of  the 
gases,  but  if  the  temperature  of  the  chimney-gases  is  low,  economy 
also  being  low  and  furnace  temperature  high,  this  would  indicate  that 
the  gases  have  been  cooled  by  the  cold  air  entering  through  leaks  in 
the  brick-work.  Chemical  analysis  of  the  gases  also  furnishes  a  means 
of  proving  the  existence  of  air-leaks.  Samples  of  gas  are  taken  simul- 
taneously from  a  point  near  the  furnace  and  from  a  point  near  the 
damper.  If  the  latter  sample  shows  on  analysis  a  greater  percentage 
of  free  oxygen  than  the  former,  it  proves  the  admission  of  air  into 
the  gases  between  the  points  from  which  the  two  samples  are  taken. 

If  the  supply  of  air  to  the  coal  in  the  furnace  is  sufficient  to  insure 
complete  combustion,  any  additional  supply,  either  in  the  furnace 
or  through  leaks  in  the  brick-work  into  the  gas-passages,  tends  to 
decrease  the  economy  of  the  boiler.  It  cools  the  gases,  decreasing  the 
difference  between  the  temperature  of  the  gases  and  that  of  the  water 
in  the  boiler,  upon  which  difference  the  transmission  of  heat  through 
the  heating  surface  depends,  and  the  excess  of  air  supply  finally  escapes 
at  the  temperature  of  the  chimney  gases,  thus  causing  a  direct  loss  of 
heat.  If,  however,  the  supply  of  air  in  the  furnace  is  insufficient  to 
thoroughly  burn  the  coal,  a  slight  leak  of  air  through  the  brick-work 
may  be  of  actual  benefit  in  supplying  sufficient  air  to  burn  the  un- 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.     507 

burned  fuel  gases  in  the  gas-passages,  although  this  air  had  better  be 
introduced  into  the  furnace  itself. 

In  well-constructed  brick-work  settings,  with  all  cracks  in  the  joints 
carefully  plastered,  the  amount  of  loss  of  heat  due  to  leaks  of  air  is 
probably  very  small,  but  large  cracks  may  cause  a  serious  loss  of 
economy,  and  they  should  be  looked  for  carefully  and  stopped  if  found. 

Improper  Firing. — Improper  firing  is  probably  the  most  common 
of  all  the  many  causes  of  poor  economy  of  steam-boilers.  Sometimes 
the  fact  that  an  improper  method  of  firing  is  used  can  be  learned  by 
simple  observation,  but  oftener  it  can  only  be  known  after  making  a 
series  of  systematic  experiments.  There  are  some  kinds  of  firing, 
practiced  by  ignorant  or  negligent  firemen,  which  any  one  who  knows 
anything  of  the  subject  can  say  at  once  are  wrong.  Among  them  are : 
(1)  Putting  a  large  quantity  of  coal  in  the  furnace  at  a  time,  covering 
the  bed  so  thickly  that  the  air-supply  is  choked  and  incomplete  com- 
bustion necessarily  takes  place.  (2)  Firing  at  irregular  intervals  and 
occasionally  allowing  the  bed  of  coal  to  burn  so  low  that  a  great 
excess  of  air  passes  through  it.  (3)  Neglecting  to  cover  the  whole  of 
the  grate  surface,  and  allowing  holes  to  form  in  the  bed  of  coal. 

There  are  other  errors  of  firing  which  are  not  evident  on  ordinary 
inspection,  which  may  be  practiced  by  the  most  careful  and  intelligent 
firemen  without  any  suspicion  that  they  are  wrong,  and  which  can 
only  be  discovered  by  making  a  series  of  boiler-tests  or  by  analysis  of 
the  chimney-gases.  Such  errors  are  the  carrying  of  a  bed  of  coal 
either  too  thick  or  too  thin  for  the  size  of  coal  and  the  force  of  draft, 
and  unskilful  regulation  of  the  draft.  The  best  method  of  firing  is  such 
a  method  as  will  cause  the  chimney-gases  to  contain  no  carbon  mon- 
oxide, hydrogen,  or  hydrocarbon  gases,  and  at  the  same  time  to  con- 
tain not  more  than  about  6  per  cent  of  free  oxygen.  The  presence  of 
combustible  gases,  even  in  small  quantity,  in  the  chimney-gas  is  proof 
of  imperfect  combustion  and  consequent  loss  of  economy.  The 
presence  of  from  3  to  6  per  cent  of  free  oxygen  in  the  chimney-gas 
is  usually  a  necessary  accompaniment  of  complete  combustion,  but  a 
greater  quantity  of  free  oxygen  means  an  unnecessarily  large  supply 
of  air,  and  consequent  unnecessary  loss  due  to  carrying  the  excess  of 
heated  air  into  the  chimney. 

The  percentage  of  carbon  dioxide  in  the  gas  is  of  itself  not  as  good 
a  criterion  of  the  furnace-conditions  as  the  percentage  of  oxygen. 

The  following  figures,  taken  from  the  table  on  page  28,  show  that 
low  C02  is  compatible  either  with  a  great  excess  or  with  a  great  de- 


508 


STEAM-BOILER  ECONOMY. 


fieiency  of  air,  both  conditions  giving  low  economy;  also  that  the  C02 
may  be  high,  over  16  per  cent,  either  from  ideal  conditions,  25  per 
cent  excess  air-supply  and  4.17  0  in  the  gas,  or  from  conditions  that 
are  far  from  ideal,  with  a  deficient  air  supply,  as  shown  in  the  third 
line  of  figures : 


C02. 

CO. 

0. 

'  N. 

Loss  Due 
CO.     B.T.U. 
per  Lb.  C. 

30%  deficit  in  air  supply  .  . 

20% 

10.94 
14  .  87 

16.41 
9  91 

0 
0 

72.65 
75.22 

6090 
4060 

10%           "          "           

18.12 

4.53 

0 

77.35 

2030 

25%  excess  air 

16  69 

o 

4  17 

79  14 

o 

50%          "       

13.91 

0 

6.95 

79.14 

0 

100%        " 

10  43 

o 

10  43 

79  14 

0 

Knowing  that  the  best  furnace-condition,  the  one  that  will  give 
maximum  economy,  is  one  that  will  cause  the  chimney-gases  to  con- 
tain from  3  to  6  per  cent  of  free  oxygen,  how  is  this  condition  to  be 
secured  ? 

If  anthracite  coal  is  the  fuel,  there  are  at  least  three  variables 
which  enter  into  the  problem:  (1)  The  size  of  coal.  (2)  The  thick- 
ness of  bed.  (3)  The  force  of  the  draft.  If  we  consider  the  size  of 
the  coal  to  be  fixed  by  the  condition  of  the  market  price  or  other  cir- 
cumstances, then  there  are  two  variables  under  control  at  the  will  of 
the  fireman,  viz.,  the  thickness  of  bed,  and  the  force  of  the  draft. 
Sometimes  the  latter  is  beyond  his  control,  as  when  the  plant  is  being 
driven  to  its  full  capacity  and  the  draft  is  limited  by  the  size  of  the 
chimney,  the  damper  area,  the  areas  of  other  gas-passages,  etc.,  but 
this  is  a  fault  in  the  plant  which  should  not  -exist.  The  chimney 
ought  always  to  have  a  capacity  for  giving  a  force  of  draft  in  excess 
of  that  ordinarily  needed,  so  that  the  draft  of  each  boiler  may  be  regu- 
lated by  its  damper.  If  both  the  thickness  of  the  bed  and  the  force 
of  draft  are  under  control  of  the  fireman,  he  may  obtain  good  results 
with  either  thin,  thick,  or  medium  fires,  provided  the  force  of  the 
draft  is  regulated  in  proportion  to  the  thickness  of  the  fire.  No  rule 
can  be  given  for  this  regulation  that  will  be  of  any  service.  Each 
engineer  in  charge  of  a  plant  must  determine  for  himself,  by  experi- 
ment or  observation,  the  conditions  of  thickness  of  fire  and  the  force 
of  draft  that  will  give  the  best  results  with  the  kind  of  coal  he  is 
using. 

In  a  plant  containing  two  or  more  boilers  connected  with  a  single 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.     509 

horizontal  flue  leading  to  the  chimney,  unless  the  draft  of  each  is 
carefully  regulated  by  a  damper,  the  force  of  draft  at  each  of  the  dif- 
ferent boilers  may  greatly  vary.  If  the  force  of  draft  at  the  several 
boilers  cannot  be  equalized,  then  the  thickness  of  coal-bed  under  each 
boiler  should  be  regulated  in  proportion  to  the  draft  of  each. 

The  attention  to  the  proper  regulation  of  the  thickness  of  the  bed 
of  coal  to  the  force  of  the  draft,  which  is  here  recommended,  may 
seem  to  be  an  unnecessary  refinement,  involving  more  trouble  than 
any  value  that  may  be  gained  from  it,  but  if  a  saving  of  only  1  or  2 
per  cent  may  be  made  thereby,  is  it  not  worth  the  trouble  ? 

There  are  almost  no  records  of  experiments  available  to  show  the 
relative  results  obtained  by  different  methods  of  firing  anthracite  coal, 
but  there  are  hundreds  of  records  of  tests  with  anthracite  coal  showing 
differences  of  economy  of  over  20%,  which  differences  are  not  satis- 
factorily explained  by  differences  in  the  type  or  proportions  of  boiler, 
in  kind  of  coal,  rate  of  driving,  or  in  anything  else  in  the  record.  It 
is  highly  probable  that  many  of  the  low  results  are  clue  to  improper 
regulation  of  the  thickness  of  the  fire.  If  such  low  results  are  obtained 
in  boiler-tests,  in  which  efforts  are  made  to  obtain  good  results,  it  is 
probable  that  much  lower  results  are  obtained  in  every-day  practice, 
in  which  boilers  are  fired  year  in  and  year  out  without  any  tests  being 
made  to  determine  their  economy. 

A  notable  result  of  the  loss  due  to  improper  firing  is  shown  in  the 
report  of  Prof.  Walter  R.  Johnson  of  the  tests  he  made  for  the  United 
States  Navy  Department  in  1842  and  1843.*  He  tested  seven  differ- 
ent anthracite  coals,  six  of  them  giving  an  evaporation  ranging  from 
11.15  to  11.59  pounds,  averaging  11.42  pounds  of  water  from  and  at 
212°  per  pound  of  combustible,  and  the  seventh,  a  Lehigh  coal,  only 
10.26  pounds,  or  over  10%  less  than  the  average  of  the  other  six  coals. 
Prof.  Johnson,  in  his  report,  gives  no  hint  of  the  real  reason  why  the 
Lehigh  coal  gave  such  a  low  figure,  but  he  gives  an  analysis  of  the 
chimney-gases  which  shows  the  extremely  low  figure  of  4.57  for  the 
percentage  of  carbon  dioxide,  and  the  very  high  figure  of  16.7  for  the 
percentage  of  oxygen.  From  this  analysis  he  calculates  that  47.9 
pounds  of  air  were  required  to  burn  one  pound  of  the  fuel,  an  amount 
which  is  more  than  double  that  required  to  burn  the  other  coals. 
He  says  that  the  large  proportion  of  unchanged  air  in  the  chimney- 
gases  is  probably  due  in  some  degree  to  the  obstruction  which  the  air 

*  Engineering  and  Mining  Journal 'October  24  and  31,  1891. 


510  STEAM-BOILER  ECONOMY. 

meets  in  arriving  at  the  surface  of  the  coal,  from  the  coat  of  ashes 
which  covers  its  surface  during  its  combustion.  He  explains  the  ex- 
istence of  this  coat  of  ashes  forming  on  this  coal  more  than  on  all 
others,  as  being  due  to  the  purity  of  the  ashes  themselves,  which  hin- 
ders their  vitrification  and  flowing  away. 

The  true  reason  of  Prof.  Johnson's  low  results  with  this  Lehigh 
coal  is  no  doubt  that  he  used  too  thin  a  bed  of  coal  on  the  grate  for 
the  amount  of  draft  he  had.  The  rate  of  combustion  was  very  low, 
6.52  to  7.71  pounds  of  coal  per  square  foot  of  grate  per  hour,  or  only 
half  of  that  commonly  used  in  good  modern  practice.  If  he  had 
attempted  to  increase  the  rate  of  combustion  by  increasing  the  draft, 
leaving  the  thickness  of  the  bed  the  same,  he  might  have  chilled  the 
fire  so  as  to  put  it  out,  but  if  he  had  thickened  the  bed  so  as  to  offer 
more  obstruction  to  the  passage  of  air  through  it,  he  might  have  ob- 
tained from  the  Lehigh  coal  as  good  a  result  as  he  did  with  other 
coals. 

The  difficulties  met  with  in  obtaining  the  proper  proportion  of 
thickness  of  bed  to  force  of  draft  with  anthracite  coal  are  increased 
when  we  have  to  deal  with  bituminous  coal,  since  there  are  other 
variables  in  the  problem  besides  those  of  size  of  coal,  thickness  of  bed, 
and  force  of  draft.  Chief  of  these  is  probably  the  varying  rate  of 
distillation  of  moisture  and  volatile  matter,  which  exists  not  only  with 
different  coals,  but  with  the  same  coal  during  the  intervals  between 
firings.  With  the  highly  volatile  coals  of  Illinois,  when  fired  by  hand, 
a  perceptible  change  in  the  furnace  conditions  is  made  every  minute. 
Immediately  after  firing,  the  supply  of  air  through  the  grates  is  too 
little  to  burn  the  gases  that  are  being  distilled;  a  few  minutes  later, 
when  the  gases  have  all  been  driven  off,  the  air  supply  is  apt  to  be 
excessive,  and  this  supply  increases  the  longer  the  time  which  elapses 
until  the  next  firing.  With  such  coals,  burned  in  ordinary  furnaces, 
with  hand-firing,  it  is  scarcely  possible  to  obtain  an  efficiency  as 
high  as  60%  of  the  heating  value  of  the  coal,  while  with  anthracite 
coal  75%  is  not  uncommon.  By  a  series  of  experiments,  checked  by 
analyses  of  the  chimney-gases,  it  is  possible  to  arrive  at  almost  ideal 
furnace  conditions,  and  hence  to  discover  the  proper  method  of  firing 
of  anthracite  coal,  but  with  bituminous  coal  it  is  impossible ;  and 
hence,  with  this  latter  coal  in  ordinary  furnaces  all  kinds  of  firing 
by  hand  are  improper;  some  may  be  worse  than  others,  but  they  are 
all  bad.  Millions  of  tons  of  coal  are  wasted  every  year  in  the  bitumin- 
ous coal  districts  by  improper  kinds  of  furnaces  and  improper  firing. 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.     5ll 

Remedies,  however,  are  available  in  improved  styles  of  furnace,  in 
mechanical  stoking,  and  in  regulation  of  the  air  supply  in  accordance 
with  the  indications  of  apparatus  for  analyzing  the  flue  gases. 

Insufficient  Heating  Surface. — A  common  complaint  made  by  the 
purchaser  of  a  new  steam-boiler  is  "The  boiler  does  not  make  enough 
steam."  The  complaint  requires  an  immediate  investigation,  and  an 
evaporation  test  should  be  made  to  determine  how  much  steam  it 
actually  makes.  The  boiler  has  probably  been  guaranteed  to  make  a 
certain  amount,  say  3  or  4  pounds  per  hour  for  each  square  foot  of 
heating  surface.  If  the  test  shows  that  it  makes  less  than  this  amount, 
the  trouble  will  usually  be  found  to  be  not  insufficient  heating  sur- 
face, but  either  deficient  draft,  insufficient  grate  surface  for  the  kind 
of  coal  used  and  for  the  draft  available,  choking  up  the  grate  by 
clinker,  or  short-circuiting  of  the  gases.  The  remedies  to  be  applied 
are  such  as  will  insure  the  burning  of  sufficient  coal  and  such  an 
arrangement  of  the  gas-passages  as  will  prevent  the  short-circuiting. 
If,  however,  the  boiler  is  found  to  be  evaporating  the  amount  of  water 
guaranteed,  the  seller  is  relieved  of  his  responsibility,  and  he  may 
properly  tell  the  purchaser  that  the  heating  surface  is  insufficient,  or 
in  other  words,  that  the  purchaser  bought  too  small  a  boiler.  The 
purchaser  may  reply  to  this  that  he  has  other  boilers  which  are  evapo- 
rating from  6  to  8  pounds  of  water  per  hour  per  square  foot  of  heating 
surface,  and  an  evaporation  test  may  show  that  his  statement  is  correct. 
It  is  very  apt  to  show  also,  however,  that  the  boilers  which  are  driven 
at  this  rate  are  wasting  fuel  by  being  overdriven.  The  purchaser 
then  has  the  option  of  taking  means,  such  as  increasing  the  area  of 
the  grate  surface  and  the  force  of  draft,  which  will  cause  the  new 
boiler  to  burn  more  coal  and  so  drive  it  up  at  the  rate  of  6  or  8  pounds 
per  hour  per  square  foot  of  heating  surface,  thus  wasting  coal,  or  of 
buying  additional  boilers  sufficient  to  give  the  required  amount  of 
steam  at  the  rate  of  3  or  4  pounds,  and  thus  saving  fuel.  Whether  he 
will  do  the  one  or  the  other  will  depend  on  the  price  of  coal  and 
whether  the  saving  will  warrant  the  extra  investment.  The  general 
relation  of  rate  of  driving  to  economy  of  fuel  varies  so  greatly  with 
different  circumstances  that  it  is  advisable  in  each  case  of  the  kind 
under  consideration  to  make  a  series  of  tests  to  determine  this  relation 
for  a  particular  plant  before  deciding  whether  to  purchase  additional 
boilers  or  to  drive  those  already  in  place  at  a  more  rapid  rate. 

If  a  test  is  made  of  each  boiler  in  the  plant  under  regular  working 
conditions  it  will  sometimes  be  found  that  no  two  of  the  boilers  are 


512  STEAM-BOILER  ECONOMY. 

driven  at  the  same  rate,  and  that  an  equalizing  or  regulation  of  the 
draft  at  the  several  boilers  will  effect  an  important  saving  of  fuel  and 
may  increase  the  total  capacity  so  as  to  make  the  purchase  of  addi- 
tional boilers  unnecessary.  The  author  once  made  a  test  of  three 
boilers  in  the  same  plant.  The  first  was  a  long  distance  from  the 
chimney ;  it  had  a  small  grate  and  large  heating  surface,  and  the  draft 
was  insufficient  to  cause  it  to  develop  its  rated  capacity.  The  second 
had  a  very  large  grate  surface,  was  close  to  the  chimney,  had  a  power- 
ful draft,  and  was  developing  double  its  rating,  while  wasting  30%  of 
the  fuel  as  compared  with  the  other  boilers.  The  third  was  between 
the  other  two  in  location;  the  size  of  grate  and  draft  were  so  related 
to  each  other  that  it  developed  a  little  more  than  its  rating  and  gave 
a  very  high  economy.  The  evident  remedy  in  this  case  was  to  cut 
down  the  grate  surface  and  check  the  draft  in  the  second  boiler,  and 
to  increase  both  the  grate  surface  and  the  draft  in  the  first  boiler. 
The  total  horse-power  developed  by  the  three  boilers  would  then  be 
the  same,  but  about  10%  of  the  fuel  would  have  been  saved,  and  by 
then  increasing  the  draft  on  all  the  boilers  a  greater  horse-power 
could  be  developed  with  the  original  consumption  of  fuel. 

Insufficient  heating  surface  is  a  most  serious  evil,  and  it  is  "often 
unsuspected  if  evaporation  tests  are  not  made.  It  is  always  the  cause 
of  waste  of  fuel,  but  if  the  boilers  give  all  the  steam  that  is  desired, 
the  grate  surfaces,  draft  and  quality  of  coal  being  such  that  the  boilers 
may  be  driven  far  beyond  their  economical  rating,  their  waste  of  fuel 
may  never  be  discovered,  because  they  are  never  tested. 

Bad  Water. — The  troubles  arising  from  the  character  of  the  water 
used  for  steam-boilers  are  of  three  different  kinds:  1,  foaming;  2, 
corrosion;  3,  incrustation  or  scale.  Sometimes  all  these  troubles  exist 
at  the  same  time. 

Cause  of  Foaming  in  Boilers. — Boilers  foam  on  the  introduction 
of  alkaline  water  only  because  the  alkali  throws  into  suspension  the 
calcium  and  magnesium  compounds  originally  dissolved  in  the  water 
and  also  much  of  the  scale  attached  to  the  tubes  and  sheets  of  the 
boiler.  Under  ordinary  conditions  of  service,  boiler  foaming  takes 
place  only  in  the  presence  of  particles  of  matter  suspended  in  the 
water  in  the  boiler.  In  the  laboratory,  boiling  distilled  water  does 
not  foam  on  the  addition  of  pure  sodium  carbonate,  but  does  foam 
vigorously  on  the  introduction  of  some  fine  insoluble  powder  such 
as  calcium  carbonate  or  magnesia  alba.  (C.  Herschel  Koyl,  R.  R. 
Gazette,  June  13,  1902.) 


BOILER  TROUBLES  AND  BOILER   USERS'   COMPLAINTS.     513 

The  remedies  for  foaming  are:  filtration  of  the  water  to  remove 
suspended  matter;  chemical  treatment  to  neutralize  some  of  the  free 
alkali  and  subsequent  filtration ;  the  use  of  a  surface  blow-off. 

Corrosion  is  due  to  the  presence  in  the  water  of  some  oxidizing 
agent,  such  as  air,  carbon  dioxide  gas,  free  acids,  or  dissolved  salts,  such 
as  magnesium  chloride,  which  have  a  corrosive  action  upon  iron  and 
steel.  The  purest  waters,  such  as  rain-water  and  melted  snow,  gen- 
erally contain  dissolved  gases,  and  sometimes  sulphuric  acid,  obtained 
from  the  atmosphere  in  localities  where  great  quantities  of  coal  con- 
taining sulphur  are  burned,  and  these  waters  if  used  in  boilers,  the 
inner  surfaces  of  which  are  clean  and  unprotected  by  a  coating  of 
scale,  may  cause  pitting  of  the  plates,  or  more  or  less  general  corro- 
sion. The  corrosion  produced  by  such  waters  may  usually  be  pre- 
vented by  occasionally  adding  a  little  milk  of  lime  to  the  water,  just 
enough  to  cause  a  very  thin  coating  of  scale  upon  the  plates.  Pitting, 
which  is  due  to  dissolved  gases,  occurs  when  the  boiler  is  merely  warm 
to  a  much  greater  extent  than  when  it  is  hot  and  in  service.  When  a 
boiler  is  to  be  kept  out  of  service  for  any  length  of  time,  particular 
care  should  be  taken  to  insure  that  the  water  in  it,  if  it  has  any 
corrosive  tendency,  should  be  neutralized  by  the  addition  of  milk  of 
lime. 

Distilled  water,  such  as  that  obtained  from  the  returns  of  steam- 
heating  systems,  in  which  exhaust  steam  is  used,  and  from  surface- 
condensers,  is  also  apt  to  be  corrosive,  due  to  the  accumulation  in  it 
of  fatty  acids  generated  by  the  decomposition  of  the  vegetable  or 
animal  oils,  which  are  often  used  in  "compounded"  lubricating  oils. 
When  such  water  is  used,  the  oil  should  be  -removed  from  it  as  much 
as  possible  before  it  enters  the  boiler,  and  the  acid  should  be  neutral- 
ized by  the  addition  of  a  very  small  amount  of  alkali. 

A  much  more  important  and  more  dangerous  cause  of  corrosion 
than  those  above  mentioned  is  the  use  of  water  containing  free  sul- 
phuric acid,  or  acid  salts,  such  as  is  often  found  in  streams  in  the 
vicinity  of  coal-mines,  or  in  streams  polluted  by  the  discharge  into 
them  of  refuse  from  dye-works,  chemical  factories,  and  other  manu- 
facturing establishments.  When  such  water  is  the  only  kind  available 
for  a  steam-boiler,  then  it  is  necessary,  in  order  to  prevent  its  corrod- 
ing the  boiler,  to  neutralize  the  acid  by  adding  an  alkali,  such  as 
carbonate  of  soda,  to  the  water.  The  presence  of  acid  in  the  water 
in  a  boiler  may  be  tested  by  drawing  a  small  sample  from  the  bottom 
gage-cock  and  inserting  into  it  a  piece  of  blue  litmus  paper,  which 


514  STEAM-BOILER  ECONOMY. 

may  be  obtained  at  a  drug-store.  If  there  is  free  acid  in  the  water 
the  blue  color  in  the  paper  will  be  changed  to  red.  By  adding  alkali 
to  the  acid  water,  drop  by  drop,  and  stirring  thoroughly,  the  red  color 
will  be  changed  back  to  blue  as  soon  as  the  alkali  becomes  in  excess. 
In  order  to  determine  the  quantity  of  carbonate  of  soda  which  should 
be  added  to  acid  feed-water  to  neutralize  the  acid,  a  pint  of  it  may  be 
taken  from  the  supply  pipe  (not  from  the  boiler,  as  there  the  acid  may 
have  become  concentrated  by  evaporation),  and  a  strip  of  blue  litmus 
paper  be  immersed  in  it  for  half  its  length,  and  allowed  to  remain  a 
minute  or  two.  The  blue  color  of  the  wetted  portion  will  change  to 
purple  if  the  water  is  very  slightly  acid,  and  to  red  if  it  is  more 
strongly  acid.  Then  add  carefully  a  solution  of  carbonate  of  soda, 
say  1  ounce  dissolved  in  a  quart  of  water,  until  the  purple  color  begins 
to  change  to  blue  or  the  red  to  purple.  Measuring  the  quantity  of  the 
solution  which  has  been  required  to  effect  the  slightest  change  of  color 
gives  us  a  means  of  estimating  the  amount  of  carbonate  of  soda  which 
is  needed  to  neutralize  the  acid  in  a  given  amount  of  acid  feed-water, 
and  make  it  silghtly  alkaline.  When  the  water  is  exactly  neutral,  it 
will  not  change  the  color  of  either  red  or  blue  litmus  paper.  When 
the  proportion  of  alkaline  water  of  a  known  strength  required  to 
neutralize  the  acid  in  the  feed-water  has  thus  been  determined,  it  may 
be  added  to  the  water  either  in  the  supply-tank,  or  pipe,  in  the  feed- 
water  heater,  or  in  the  boiler,  as  may  be  most  convenient.  When  a 
feed-water  heater  is  used  the  alkali  should  be  added  either  in  it  or  in 
the  supply  before  the  water  reaches  the  heater,  for  if  not  added  until 
after  the  water  passes  the  heater,  the  acid  will  corrode  the  heater.  It 
is  better  always  to  add  the  alkali  in  the  supply-tank,  for  the  acid  is 
apt  to  corrode  the  pump  and  the  pipes,  as -well  as  the  heater  and  the 
boiler. 

When  the  feed-water  contains  simply  free  acid  without  any  im- 
portant amount  of  scale-formng  material,  such  as  lime  or  magnesia, 
the  treatment  by  carbonate  of  soda  is  usually  all  that  is  necessary,  but 
if  lime  or  magnesia  or  both  are  present,  the  treatment  becomes  a 
more  complicated  matter,  and  it  is  then  most  desirable  to  call  in 
the  services  of  a  chemist  who  is  expert  in  the  treatment  of  bad  feed- 
waters  and  take  his  advice  as  to  method  of  purification  to  be 
adopted.  In  such  cases  it  will  usually  be  necessary  to  use  large  settling- 
tanks,  adding  caustic  lime  or  carbonate  of  soda,  or  both,  for  precipi- 
tating and  settling  out  the  hydrate  or  carbonate  of  lime  formed  by  the 
chemical  reaction,  or  else  to  use  a  live-steam  feed- water  heater,  after 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    515 

neutralizing  the  water  with  carbonate  or  caustic  soda,  in  which  the 
scale-forming  materials  will  be  deposited.  It  is  necessary  always  to 
avoid  using  an  excess  of  soda  or  other  alkali,  for  such  excess  is  apt  to 
cause  foaming.  As  the  quality  of  the  water  is  apt  to  vary  from  time 
to  time,  the  impurities  diminishing  in  rainy  seasons  and  increasing  in 
times  of  drought,  it  is  advisable  to  have  tests  of  the  water  made 
frequently,  and  to  vary  the  amount  of  reagents  used  in  accordance 
with  the  results  of  these  tests.  Organic  matter,  contained  in  sewage  or 
in  water  from  swamps,  peat-bogs,  etc.,  is  sometimes  a  cause  of  corro- 
sion, which  may  be  prevented  by  proper  chemical  treatment. 

Kerosene  oil,  which  is  sometimes  used  as  a  scale  preventive,  is  said 
to  be  sometimes  a  cause  of  corrosion,  due  to  the  fact  that  the  oil  may 
contain  traces  of  the  sulphuric  acid  which  was  used  in  its  purification. 
Water  containing  chloride  of  magnesium  is  apt  to  be  corrosive,  since 
this  salt  decomposes  at  high  temperatures,  liberating  free  acid.  The 
acid  may  be  neutralized  by  carbonate  of  soda. 

Weakening  of  the  plates  by  corrosion  is  one  of  the  greatest  dangers 
to  which  boilers  are  liable,  and  it  should  be  guarded  against  by  fre- 
quent and  thorough  inspection  of  the  interior  by  a  competent  inspector, 
and  whenever  it  is  found  no  expense  should  be  spared  to  prevent  its 
continuance.  If  the  corrosion  is  trifling  in  amount,  some  simple  remedy 
may  usually  be  found,  such  as  rendering  the  water  slightly  alkaline 
by  lime-water  or  carbonate  of  soda. 

Sometimes  a  remedy  is  found  in  hanging  zinc  plates  in  the  water 
in  the  boiler,  suspending  them  by  wires  or  rods  which  are  soldered  to 
the  upper  part  of  the  shell,  so  as  to  make  an  electric  connection,  the 
zinc,  the  steel  plates  of  the  boiler,  and  the  corrosive  water  thus  forming 
a  galvanic  battery,  the  zinc  being  eaten  away  and  the  iron  being  thus 
protected. 

The  following  note  on  the  use  of  zinc  is  taken  from  a  report  by  the 
Committee  on  Boilers  of  the  Institution  of  Mechanical  Engineers 
(1884)  : 

Of  all  the  preservative  methods  adopted  in  the  British  service,  the 
use  of  zinc  properly  distributed  and  fixed  has  been  found  the  most 
effectual  in  saving  the  iron  and  steel  surfaces  from  corrosion,  and  also 
in  neutralizing  by  its  own  deterioration  the  hurtful  influences  met 
with  in  water  as  ordinarily  supplied  to  boilers.  The  zinc  slabs  now 
used  in  the  navy  boilers  are  12  in.  long,  6  in.  wide,  and  y%  in.  thick ; 
this  size  being  found  convenient  for  general  application.  The  amount 
of  zinc  used  in  new  boilers  at  present  is  one  slab  of  the  above  size  for 
every  20  I.H.P.,  or  about  one  square  foot  of  zinc-surface  to  two  square 


516  STEAM-BOILER  ECONOMY. 

feet  of  grate-surface.  Boiled  zinc  is  found  the  most  suitable  for  the 
purpose.  To  make  the  zinc  properly  efficient  as  a  protector  especial 
care  must  be  taken  to  insure  perfect  metallic  contact  between  the 
slabs  and  the  stays  or  plates  to  which  they  are  attached.  The  slabs 
should  be  placed  in  such  positions 'that  all  the  surfaces  in  the  boiler 
shall  be  protected.  Each  slab  should  be  periodically  examined  to  see 
that  its  connection  remains  perfect,  and  to  renew  any  that  may  have 
decayed;  this  examination  is  usually  made  at  intervals  not  exceeding 
three  months.  Under  ordinary  circumstances  of  working  these  zinc 
slabs  may  be  expected  to  last  in  fit  condition  from  sixty  to  ninety 
days  immersed  in  hot  sea-water ;  but  in  new  boilers  they  at  first  decay 
more  rapidly.  The  slabs  are  generally  secured  by  means  of  iron  straps 
2  in.  wide  and  %  in.  thick,  and  long  enough  to  reach  the  nearest  stay, 
to  which  the  strap  is  firmly  attached  by  screw-bolts. 

On  the  same  subject  The  Locomotive  says: 

Zinc  is  often  used  in  boilers  to  prevent  the  corrosive  action  of 
water  on  the  metal.  The  action  appears  to  be  an  electrical  one,  the 
iron  being  one  pole  of  the  battery  and  the  zinc  being  the  other.  The 
hydrogen  goes  to  the  iron  shell  and  escapes  as  a  gas  into  the  steam. 
The  oxygen  goes  to  the  zinc. 

On  account  of  this  action  it  is  generally  believed  that  zinc  will 
always  prevent  corrosion,  and  that  it  cannot  be  harmful  to  the  boler 
or  tank.  Some  experiences  go  to  disprove  this  belief,  and  in  numerous 
cases  zinc  has  not  only  been  of  no  use,  but  has  even  been  harmful. 
In  one  case  a  tubular  boiler  had  been  troubled  with  a  deposit  of  scale 
consisting  chiefly  of  organic  matter  and  lime,  and  zinc  was  tried  as  a 
preventive.  The  beneficial  action  of  the  zinc  was  so  obvious  that  its 
continued  use  was  advised,  with  frequent  opening  of  the  boiler  and 
cleaning  out  of  detached  scale  until  all  the  old  scale  should  be  re- 
moved and  the  boiler  become  clean.  Eight  or  ten  months  later  the 
water-supply  was  changed,  it  being  now  obtained  from  another  stream 
supposed  to  be  free  from  lime  and  to  contain  only  organic  matter. 
Two  or  three  months  after  its  introduction  the  tubes  and  shell  were 
found  to  be  coated  with  an  obstinate  adhesive  scale,  composed  of  zinc 
oxide  and  the  organic  matter  or  sediment  of  the  water  used.  The 
deposit  had  become  so  heavy  in  places  as  to  cause  overheating  and 
bulging  of  the  plates  over  the  fire. 

H.  A.  Wyckoff,  Power,  November  12,  1912,  writes  as  follows  con- 
cerning the  placing  of  zinc  slabs  in  boilers  to  prevent  pitting: 

"I  have  found  the  best  way,  for  convenience  in  cleaning  out  and 
making  renewals,  to  be  to  construct  a  pan  of  %-in.  iron,  any  size 
to  suit  the  conditions  and  shape  of  the  braces,  and  suspend  it  from 
the  braces  so  it  will  clear  the  top  row  of  tubes  by  2  or  3  inches. 
Turn  up  the  edges  of  the  pan  not  less  than  2  inches  and  drill  a 
number  of  small  holes  in  the  bottom.  In  a  few  weeks,  depending  on 
the  aciditv  of  the  water,  the  zinc  will  have  pulverized  and  become  like 
gravel — depending  on  the  amount  of  dross  in  it. 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    517 

"If  the  back  end  of  tubes  and  shell  show  most  pitting,  hang  the 
basket  or  pan  at  that  end;  if  the  front  end  is  most  affected,  put  it 
there." 

In  the  same  issue  of  Power,  J.  C.  Hawkins  describes  as  follows 
the  method  of  using  zinc  in  the  boilers  of  U.  S.  battleships : 

"An  iron  box  is  made  of  ^-in.  material  12  in.  wide  by  40  in. 
long,  and  13  in.  deep.  Large  holes  are  cut  in  the  sides  and  bottom, 
and  the  top  is  left  open.  This  is  suspended  from  the  shell  of  the 
steam  drum  and  comes  just  below  the  water  line.  In  this  box  are 
placed  18  slabs  of  zinc,  each  l2xl2xl/2  in. — set  six  in  a  row,  or  a 
total  of  about  333  pounds  in  each  boiler.  These  slabs  are  set  on 
edge  in  the  box  with  holes  drilled  in  them  and  through  the  box, 
through  which  %-:m-  rods  are  run  with  large  nuts  or  washers  between 
the  slabs  to  hold  them  in  place  and  about  1*4  inches  apart.  The  rods 
have  a  split  pin  through  the  end  to  keep  them  in  place.  This  ar- 
rangement exposes  the  greatest  surface  of  zinc  to  the  action  of  the 
water  which  passes  through  the  holes  in  the  box  and  around  the 
plates  of  zinc.  The  action  of  the  water  on  these  slabs  causes  them 
to  waste  away,  but  when  they  are  taken  out  there  is  a  coating  of 
scale  on  them  which  often  entirely  fills  up  the  space  between  the 
slabs.  This  scale  is  easily  cracked  off  when  dry,  and  leaves  the  slabs 
about  one-quarter  or  one-half  their  original  thickness.  These  slabs, 
if  too  thin,  are  not  used  again. 

"The  water  used  in  the  boilers  of  these  ships,  although  coming 
from  the  evaporators,  is  more  or  less  salty  and  contains  chemicals 
that  cause  galvanic  action  and  pitting.  When  zinc  is  used  the  gal- 
vanic action  takes  place  on  the  zinc  instead  of  on  the  boiler,  as  zinc 
has  a  stronger  attraction  for  the  acids  than  the  iron. 

"In  one  battleship  there  are  16  water- tube  boilers  with  a  total 
of  29,000  H.P.,  or  1812  H.P.  each.  Each  boiler  has  one  box  of 
these  zinc  plates.  I  should  judge  that  10  to  15  Ib.  of  zinc  slabs  sus- 
pended in  the  drum  just  below  the  water  line,  or  about  7  Ib.  per 
100  boiler-H.P.  would  be  sufficient  for  a  stationary  boiler." 

Painting  Boiler  Shells  to  Prevent  Pitting. — Zinc  paint  is  reported 
to  have  given  satisfactory  results  as  a  preventive  of  pitting,  and  a 
correspondent  of  Power  writes  that  boilers  that  were  corroding  and 
pitting  rapidly  were  prevented  from  further  deterioration  by  first 
cleaning  the  plates  thoroughly  with  a  scraper  and  a  wire  brush,  then 
painting  them  with  a  paint  made  of  linseed  oil  and  Portland  cement, 
and  after  this  had  dried,  with  a  second  coat  made  with  one  part 
graphite  and  three  parts  cement.  In  three  years  after  this  treatment 
the  pitting  had  not  extended. 

If  the  corrosion  is  serious  it  may  be  necessary  either  to  change  the 
feed-water  or,  if  this  is  not  practicable,  to  treat  it  with  chemicals  in 
tanks  and  filter  it  before  allowing  it  to  enter  the  boiler. 


518 


STEAM-BOILER  ECONOMY. 


Grooving  or  channelling  is  a  kind  of  local  corrosion,  usually  found 
adjacent  to  the  seams  of  the  shell  of  a  boiler.  It  is  commonly  due  to 
a  combination  of  slightly  acidulated  water  and  of  strains  in  the  boiler- 
shell  due  to  expansion  and  contraction,  which  cracks  the  scale  off  the 
shell  and  exposes  the  clean  metal.  It  is  an  extremely  dangerous  form 

of  corrosion,  and   calls   for   an   im- 
mediate remedy. 

Fig.  237  shows  an  example  of  pit- 
ting, and  Fig.  238  one  of  grooving. 


o 
o 
o 
o 
o 
o 

V2- 


o  o  o  o  o  o 

00000 


FIG.  237.— A  PLATE  BADLY  FITTED. 


FIG.  238. — GROOVING  AT  A  LAP  JOINT. 


Incrustation  or  Scale. — The  formation  of  scale  is  the  most  com- 
mon of  all  boiler  troubles.  It  is  due  to  the  presence  in  the  feed-water 
of  various  substances,  some  of  which,  such  as  clay  and  finely  divided 
vegetable  or  organic  matter,  are  carried  in  suspension  and  others  are 
carried  in  solution.  Of  the  substances  that  are  held  in  solution,  some, 
such  as  carbonate  of  lime,  are  precipitated  by  heating  to  a  tempera- 
ture of  212° ,  others,  such  as  sulphate  of  lime,  are  precipitated  to 
some  extent  at  higher  temperatures.  Still  others,  such  as  common 
salt,  cannot  be  precipitated  at  all,  but  remain  in  solution  until  enough 
water  is  evaporated  away  to  cause  the  solution  to  become  saturated ; 
that  is,  holding  the  greatest  possible  quantity  of  salt  in  solution,  when 
the  salt  begins  to  crystallize,  and  it  will  then  rapidly  form  a  coating 
on  the  boiler-surfaces. 

When  the  scale-forming  material  is,  like  common  salt,  incapable 
of  being  precipitated  by  heating,  but  capable  of  forming  solid  masses 
by  concentration  and  crystallization,  it  may  to  some  extent  be  pre- 
vented from  forming  scale  by  frequent  blowing  off,  so  as  to  keep  the 
strength  of  the  brine  below  the  saturation-point.  This  was  the  old 
practice  with  marine  boilers  using  sea-water,  before  surface-condensers 
and  feed-water  evaporators  came  into  use.  It  is  still  the  only  method 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    519 

by  which  salt  water  can  be  used  in  a  steam-boiler.  Sea-water,  how- 
ever, contains  sulphate  of  lime  and  other  impurities  which  will  be 
precipitated  and  make  scale  at  high  temperatures. 

When  the  scale-forming  material  is  carried  in  suspension  in  the 
water,  whether  in  the  original  cold  feed-water,  as  in  the  case  of  clay 
in  muddy  water,  or  in  fine  particles  precipitated  by  heat  in  the  feed- 
water  heater  or  in  the  boiler,  or  by  the  addition  of  chemicals,  the 
evaporation  of  the  water  in  the  boiler  will  cause  this  material  to 
accumulate,  and  it  will  give  rise  to  trouble  unless  it  is  removed.  It 
is  apt  to  take  any  one  of  three  forms;  sometimes  all  three  of  them 
may  be  formed  from  the  same  water.  The  first  is  scum,  which  floats 
on  top  of  the  water,  and  may  be  removed  by  a  scum-collector  and  a 
surface  blow-off.  The  second  is  soft  mud,  which,  while  it  is  in  a  very 
soft,  almost  liquid  condition,  may  be  blown  out  through  the  blow-off 
'valve,  or  when  the  boiler  is  laid  off  for  cleaning  may  be  washed  out 
with  a  jet  of  water  from  a  hose.  The  third  is  solid  scale,  ranging 
from  a  soft  chalk  which  may  easily  be  broken  by  the  fingers,  to  hard 
cement  or  a  porcelain-like  substance  which  it  is  difficult  to  break  or 
cut  by  a  hammer  and  chisel. 

The  scum,  which  at  first  floats  on  the  surface,  will,  if  allowed  to 
accumulate,  sink  and  be  deposited  on  the  tubes  or  shell  of  the  boiler, 
and  will  become  either  mud  or  scale.  The  mud,  which  may  be  washed 
out  of  the  boiler,  may  also  become  cemented  by  the  other  substances 
precipitated  from  the  water,  or  may  be  baked  on  the  shell.  Scale 
attaches  itself  to  all  the  metal  surfaces  of  the  boiler,  including  tubes, 
rivet-heads,  braces,  etc.,  as  well  as  to  the  shell. 

The  effect  of  scale  in  a  boiler  ordinarily  is  to  reduce  both  its  steam- 
generating  capacity  and  its  economy,  since  it  is  not  a  good  conductor 
of  heat,  and  therefore  diminishes  the  transmission  of  heat  through  the 
plates.  It  is  also  often  highly  dangerous,  whenever  it  accumulates 
to  such  an  extent,  at  a  part  of  the  shell  which  is  exposed  to  flame,  or 
to  very  hot  gases,  that  the  plates  become  overheated  and  weakened. 
A  thin  scale  may  form  on  the  tubes,  be  cracked  off  by  their  expansion 
and  contraction,  or  detached  by  the  action  of  some  "boiler  com- 
pound/' and  may  then  be  carried  by  the  circulation  and  deposited  in 
a  thick  mass  on  the  shell  over  the  fire.  This  may  cause  a  "bagged5' 
plate,  or  a  crack  and  an  explosion.  If  the  scale  is  dense  and  hard,  so  as 
to  be  practically  waterproof,  a  thin  coating  of  it  may  be  an  effective 
non-conductor,  and  it  may  be  a  source  of  great  danger  as  well  as  of 
loss  of  economy.  If,  however,  it  is  porous,  as  many  scales  are,  it  will 


520  STEAM-BOILER  ECONOMY. 

allow  water  to  pass  through  it  to  the  metal  surfaces  of  the  boiler,  and 
the  decreased  transmission  of  heat  will  be  very  slight. 

Effect  of  Scale  on  Boiler  Efficiency. — The  following  statement  or 
a  similar  one  has  been  published  and  republished  for  forty  years  or 
more  by  makers  of  "boiler  compounds/'  feed-water  heaters  and  water- 
purifying  apparatus,  but  the  author  has  not  been  able  to  trace  it 
to  its  original  source  :* 

"It  has  been  estimated  that  scale  5-5  of  an  inch  thick  requires  the 
burning  of  5  per  cent  of  additional  fuel;  scale  ^oi  an  inch  thick  re- 
quires 10  per  cent  more  fuel;  ^  of  an  inch  of  scale  requires  15  per 
cent  additional  fuel;  -|  of  an  inch,  30  per  cent,  and  J  of  an  inch,  66 
per  cent." 

The  absurdity  of  the  last  statement  may  be  shown  by  a  simple 
calculation.  Suppose  a  clean  boiler  is  giving  75  per  cent  efficiency  with 
a  furnace  temperature  of  2400°  F.  above  the  atmospheric  tempera- 
ture. Neglecting  the  radiation  and  assuming  a  constant  specific  heat 
for  the  gases,  the  temperature  of  the  chimney  gases  will  be  600°.  A* 
certain  amount  of  fuel  and  air  supply  will  furnish  100  Ibs.  of  gas. 
In  the  boiler  with  ^-in.  scale  66  per  cent  more  fuel  will  make  66  Ibs. 
more  gas.  As  the  extra  fuel  does  no  work  in  evaporating  water,  its 
heat  must  all  go  into  the  chimney  gas.  We  have  then  in  the  chimney 
gases 

100  Ibs.  at     600°  F.,  product     60,000 
66  Ibs.  at  2400°  F.,  product  158,400 

218,400 

which  divided  by  166  gives  1370°  above  atmosphere  as  the  tempera- 
ture of  the  chimney  gas,  or  more  than  enough  to  make  the  flue  con- 
nection and  damper  red  hot.  (Makers  of  boiler  compounds,  etc., 
please  copy.) 

Another  writer  says :  "Scale  of  Y&  inch  thickness  will  reduce  boiler 
efficiency  -J,  and  the  reduction  of  efficiency  increases  as  the  square  of 
the  thickness  of  the  scale." 

This  is  still  more  absurd,  for  according  to  it  if  rg-in.  scale 
reduces  the  efficiency  J,  then  j^-in.  will  reduce  it  f ,  or  to  below 
zero. 

*  A  committee  of  the  Am.  Ry.  Mast.  Mechs.  Assn.  in  1872  quoted  from 
a  paper  by  Dr.  Jos.  G.  Rodgers  before  the  Am.  Assn.  for  Adv.  of  Science  (date 
not  stated):  "It  has  been  demonstrated  [how  and  by  whom  not  stated]  that  a 
scale  TS  in.  thick  requires  the  expenditure  of  15  per  cent  more  fuel.  As  the 
scale  thickens  the  ratio  increases;  thus  when  it  is  |  in.  thick,  60  per  cent  more 
is  required."  Mr.  John  Graham  in  the  "Memoirs  of  the  Literary  and  Philo- 
sophical Society"  of  Manchester,  1860,  described  some  experiments  made  by 
him  and  states  that  "a  scale  of  sulphate  of  lime  ^  in.  thick  reduced  the 
efficiency  14.7  per  cent." 


BOILER  TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    521 

From  a  series  of  tests  of  locomotive  tubes  covered  with  different 
thicknesses  of  scale  up  to  J-in.  Prof.  E.  C.  Schmidt  (Bull.  No.  11 
Univ.  of  111.  Experiment  Station,  1907),  draws  the  following  con- 
clusions : 

1.  Considering   scale   of   ordinary  thickness,   say   varying   up   to 
|;-inch,    the  loss  in  heat  transmission  due  to  scale  may  vary  in  indi- 
vidual cases  from  insignificant  amounts  to  as  much  as  10  or  12  per 
cent. 

2.  The  loss  increases  somewhat  with  the  thickness  of  the  scale. 

3.  The  mechanical  structure  of  the  scale  is  of  as  much  or  more 
importance  than  the  thickness  in  producing  this  loss. 

4.  Chemical  composition,  except  in  so  far  as  it  affects  the  structure 
of  the  scale,  has  no  direct  influence  on  its  heat-transmitting  qualities. 

In  1896  the  author  made  a  test  of  a  water-tube  boiler  at  Aurora, 
111.,  which  had  a  coating  of  scale  about  J-in.  thick  throughout  its 
whole  heating  surface,  and  obtained  practically  the  same  evaporation 
as  in  another  test,  a  few  days  later,  after  the  boiler  had  been  cleaned. 
This  is  only  one  case,  but  the  result  is  not  unreasonable  when  it  is 
known  that  the  scale  was  very  soft  and  porous,  and  was  easily  re- 
moved from  the  tubes  by  scraping. 

Prof.  R.  C.  Carpenter  (Am.  Electrician,  August,  1900),  says:  "So 
far  as  I  am  able  to  determine  by  tests,  a  lime  scale,  even  of  great 
thickness,  has  no  appreciable  effect  on  the  efficiency  of  a  boiler,  as 
in  a  test  which  was  conducted  by  myself  the  results  were  practically 
as  good  when  the  boiler  was  thickly  covered  with  lime  scale  as  when 
perfectly  clean.  .  .  .  Observations  and  experiments  have  shown 
that  any  scale  porous  to  water  has  little  or  no  detrimental  effect  on 
economy  of  the  boiler.  There  is,  I  think,  good  philosophy  for  this 
statement;  the  heating  capacity  is  affected  principally  by  the  rapidity 
with  which  the  heated  gases  will  surrender  heat,  as  the  water  and  the 
metal  have  capacities  for  absorbing  heat  more  than  a  hundred  times 
faster  than  the  gas  will  surrender  heat. 

A  thin  film  of  grease,  being  impermeable  to  water,  keeps  the  latter 
from  contact  with  the  metal  and  generally  produces  disastrous  re- 
sults. It  is  much  more  harmful  than  a  very  thick  scale  of  carbonate 
of  lime. 

Danger  from  Scale,  Dirt  and  Oil  in  Marine  Boilers.* — The  tubes 
are  likely  to  become  impaired  by  the  presence  within  them  of  air, 
oil,  dirt  or  scale.  Scale  is  the  evil  that  should  be  most  dreaded,  since 
if  care  is  exercised  the  introduction  of  dirt  or  oil  should  be  prevented. 
Since  the  water  tender  can  give  a  dose  of  salt  feed  at  any  time, 
and  as  he  will  certainly  give  such  a  supply  rather  than  run  the  risk 
of  getting  low  water,  some  salt  water  undoubtedly  goes  into  the  boiler 
every  day.  It  also  may  come  from  leaky  valves.  If  from  any  cause 

*  From  a  paper  by  H._C.  Dinger,  in  Jour.  Am.  Soc.  Naval  Engrs.,  Feb.,  1903. 


522  STEAM-BOILER  ECONOMY. 

considerable  scale  is  allowed  to  deposit,  the  tubes  are  liable  to  burn 
out.  From  salt  alone  no  serious  results  need  be  apprehended,  but 
no  salt  water  .ever  enters  without  carrying  some  scale. 

A  deposit  of  considerable  thickness  of  dirt  will  produce  conditions 
that  will  result  in  the  burning  out  of  the  tubes.  Skill  in  manage- 
ment and  judgment  in  blowing  down  will  prevent  muddy  sediment 
from  collecting.  If  dirty  water  is  used,  it  is  imperative  to  blow 
down  regularly,  so  that  dangerous  accumulations  of  sediment  can- 
not form. 

The  strictest  precaution  should  be  taken  to  prevent  as  little  oil 
as  possible  from  reaching  the  tubes.  As  it  is  imposible  to  keep  the 
tubes  entirely  clear  of  oil,  since  the  oilers  will  pour  oil  into  the 
auxiliaries,  even  if  they  are  sparing  at  the  main  engines,  some  means 
must  be  taken  to  saponify  or  to  dissolve  the  oil  in  solution  or  de- 
posited on  the  inside  of  the  tubes — then  the  oil  products  can  be  blown 
overboard.  This  can  be  done  by  the  use  of  caustic  soda,  the  amount 
required  being  determined  by  special  conditions. 

It  is  also  advisable  occasionally  to  boil  out  the  tubes  with  a  strong 
solution  of  soda.  Another  way  of  getting  rid  of  oil  is  to  introduce 
about  ten  pounds  of  soda  into  the  boiler,  then  get  up  steam  quickly. 
After  allowing  the  alkaline  water  in  the  boiler  to  stand  for  a  time 
and  thus  neutralizing  the  acid  and  dissolving  or  saponif}7ing  the  oil, 
the  surface  blow  valve  should  be  slightly  used,  and  then  the  boiler 
should  be  emptied  by  means  of  the  bottom  blow  valve.  Where  fresh 
water  is  scarce  there  will  naturally  be  a  disinclination  to  resort  to 
this  remedy. 

Another  way  is  to  pump  the  boiler  about  one-third  full  of  fresh 
water  and  then  enter  the  soda.  Admit  a  little  steam  through  the 
auxiliary  stop  valve  to  heat  the  contained  water.  Then  circulate  the 
water  through  the  boiler  by  means  of  an  auxiliary  pump,  using  any 
available  auxiliary  to  effect  this  object. 

It  is  regular  and  uniform  cleaning,  and  not  intermittent  atten- 
tion, which  will  insure  efficiency  and  safety.  The  use  of  zincs  is  also 
advisable,  the  number  and  location  of  the  baskets  or  slabs  being  de- 
pendent upon  experiment,  experience  and  character  of  the  water. 

Methods  for  Prevention  or  Removal  of  Scale. — The  methods 
of  treatment  adopted  for  the  removal  or  prevention  of  scale  are 
numerous.  The  most  common,  perhaps,  is  to  allow  it  to  accumulate 
in  the  boiler  until  it  is  thought  to  be  thick  enough  to  be  a  source 
of  danger,  or  of  loss  of  economy,  and  then  to  remove  it  by  mechani- 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.    523 

cal  means.  This  may  be  a  good  enough  method  in  some  cases,  es- 
pecially when  the  water  is  not  very  bad,  so  that  it  requires  several 
months  for  a  coating  of  objectionable  thickness  to  form,  when  the 
scale  is  of  such  a  nature  that  it  does  not  detach  itself  and  accumulate 
in  thick  patches  over  the  fire,  and  when  the  boiler  is  of  such  a  con- 
struction that  it  is  possible  to  clean  it  thoroughly,  such  as  a  water- 
tube  boiler  with  straight  tubes. 

Another  method,  commonly  used,  is  to  introduce  periodically  into 
the  boiler  a  solution  of  some  chemical,  such  as  caustic  soda,  tannate, 
carbonate  and  phosphate  of  soda,  etc.,  which  will  cause  a  change  in 
the  chemical  composition  of  the  scale-forming  material,  making  a 
precipitate  which  may  be  easily  removed  and  a  soluble  material  which 
may  be  kept  below  the  point  of  concentration  by  occasional  blowing- 
off. 

These  chemicals  form  the  base  of  many  of  the  "boiler  compounds," 
some  of  which  may  cure  the  disease,  while  many  will  not,  although 
they  are  sold  at  a  very  high  price  compared  with  the  market  value  of 
the  chemicals.  In  relation  to  these  compounds  Mr.  Albert  A.  Gary 
says: 

Never  use  any  boiler  compound  unless  you  know  positively  just 
what  it  is  composed  of,  and  how  it  will  affect  the  impurities  in  your 
boiler  and  the  boiler  itself.  In  the  treatment  of  boiler-waters,  always 
start  with  a  careful  analysis  of  the  water,  made  by  a  competent  chem- 
ist who  has  experience  in  this  line.  Next,  if  you  are  thinking  of  using 
any  chemical  that  has  been  offered  for  treatment  of  your  boiler-water, 
let  your  chemist  analyze  it.  If  you  are  dealing  with  straightforward 
people,  they  will  generally  tell  you  the  exact  composition  of  their 
material,  which  your  chemist  can  verify  easily,  after  which  he  will 
be  prepared  to  advise  properly.  (Engineering  Magazine,  June,  1897.) 

In  1885  a  report  made  by  the  Bavarian  Steam-boiler  Inspection 
Association  gave  a  list  of  twenty-seven  boiler  compounds  which  had 
been  analyzed.  It  commented  on  them  as  follows : 

All  secret  compounds  for  removing  boiler-scale  should  be  avoided. 
Such  secret  preparations  are  either  nonsensical  or  fraudulent,  or  con- 
tain either  one  of  the  two  substances  (soda  or  lime)  recommended  by 
the  Association  for  removing  scale,  generally  soda,  which  is  colored 
to  conceal  its  presence,  and  sometimes  adulterated  with  useless  or  even 
injurious  matter.  These  additions,  as  well  as  giving  the  compound 
some  strange,  fanciful  name,  are  meant  simply  to  deceive  the  boiler- 
owner  and  conceal  from  him  the  fact  that  he  is  buying  colored  soda, 
or  similar  substances,  for  which  he  is  paying  an  exorbitant  price. 


524  STEAM-BOILER  ECONOMY. 

Besides  the  methods  of  removing  the  scale  after  it  has  encrusted 
the  boiler,  and  preventing  its  formation  by  means  of  chemicals  intro- 
duced into  the  boiler  and  frequent  blowing-off,  there  are  many  ways 
of  treating  water  to  remove  its  scale-forming  material  before  allowing 
it  to  enter  the  boiler.  A  common  method,,  and  for  some  kinds  of 
water  one  of  the  best,  is  to  heat  the  water  in  an  open  feed-water  heater. 
If  the  scale-forming  material  is  simply  bicarbonate  of  lime,  that  is, 
mono-carbonate  held  in  solution  by  carbon  dioxide  gas  dissolved  in  the 
water,  it  may  be  almost  entirely  precipitated  by  continued  heating  to 
drive  off  the  carbon  dioxide  gas.  The  insoluble  carbonate  thus  precipi- 
tated will  attach  itself  to  the  plates  of  the  heater,  which  therefore 
needs  to  be  cleaned  frequently.  Even  sulphate  of  lime  can  be  precipi- 
tated to  a  considerable  extent  by  heating  it  to  about  300°  in  a  live- 
steam  feed-water  heater,  such  as  the  Hoppes. 

When  the  water  is  very  bad,  the  feed-water  heaters  may  prove 
insufficient  to  purify  it,  and  then  recourse  must  be  had  to  treatment 
of  the  water  by  chemicals  in  tanks,  and  subsequent  slow  settling  or 
nitration  to  remove  the  sediment  formed.  Hydrate  or  milk  of  lime, 
carbonate  of  soda  and  caustic  soda  are  the  chemicals  used.  This 
method  requires  a  somewhat  expensive  equipment,  and  great  care  in 
its  operation.  It  should  not  be  undertaken  without  competent  expert 
advice  together  with  chemical  analysis. 

Keresone  oil,  and  other  refined  petroleum  oils,  heavier  than  kero- 
sene, are  sometimes  used  with  good  effect  in  boilers  to  prevent  the 
scale-forming  materials  attaching  themselves  to  the  boiler.  These 
oils  appear  to  rot  the  scale  so  that  it  may  easily  be  removed.  Crude 
oil  should  never  be  used,  as  it  gives  off  inflammable  vapors,  and  leaves 
a  tarry  residuum  which  may  form  with  the  scale  a  tough,  greasy 
deposit  on  the  plates  over  the  fire  and  cause  them  to  burn  out. 

A  condensed  summary  of  the  various  causes  of  incrustation,  cor- 
rosion, etc.,  and  their  remedies,  is  given  as  follows  in  a  paper  by 
Messrs.  A.  E.  Hunt  and  G.  H.  Clapp,  in  the  Transactions  of  the 
American  Institute  of  Mining  Engineers,  vol.  xvii.  p.  338,  and 
credited  to  Prof.  L.  M.  Norton,  as  follows: 

CAUSES   OF  INCRUSTATION". 

1.  Deposition  of  suspended  matter. 

2.  Deposition  of  salts  from  concentration. 

3.  Deposition  of  carbonates  of  lime  and  magnesia  by  boiling  off 
carbonic  acid,  which  holds  them  in  solution. 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    525 

4.  Deposition  of  sulphates  of  lime,  because  sulphate  of  lime  is 
soluble  in  cold  water,  less  soluble  in  hot  water,  insoluble  above  270°  F. 

,5.  Deposit  of  magnesia,  because  certain  magnesium  salts  decompose 
at  high  temperatures. 

6.  Deposition  of  lime-soap,  iron-soap,  etc.,  formed  by  saponifica- 
tion  of  grease. 


METHODS    OF   PREVENTING   INCRUSTATION. 

1.  Filtration. 

2.  Blowing-off. 

3.  Use  of  internal  collecting  apparatus,  or  devices  for  directing 
the  circulation. 

4.  Heating  feed-water. 

5.  Chemical  or  other  treatment  of  water  in  boiler. 

6.  Introduction  of  zinc  in  boiler. 

7.  Chemical  treatment  of  water  outside  of  boiler. 


Troublesome  Substance. 
Sediment,  mud,  clay,  etc. 
Readily  soluble  salts. 
Bicarbonates  of  lime,  mag- 
nesia and  iron. 
Sulphate  of  lime. 

Chloride  of  magnesium 

Carbonate  of  soda  in  large 

amounts. 
Acid  (in  mine-water). 

Dissolved     carbonic     acid 
and  oxygen. 

Grease     (from    condensed 
water). 

Organic  matter  (sewage). 


Trouble. 
Incrustation. 
Incrustation. 

Incrustation. 

Incrustation. 

Corrosion 

Priming. 
Corrosion. 

Corrosion. 

Corrosion  or 
incrustation. 

Priming, 
corrosion  or 
incrustation 


Remedy  or  Palliation.* 

Filtration;  bio  wing-off. 

Blowing-off. 

Heating  feed;  addition  of  caus- 
tic soda,  lime,  etc. 

Addition  of  carbonate  of  soda, 
barium  hydrate,  etc. 

Addition  of  carbonate  of  soda, 
etc. 

Addition  of  barium  chloride,  etc. 

Alkali. 

Feed  milk  of  lime  to  the  boiler, 
to  form  a  thin  internal  coat- 
ing. 

Different  cases  require  different 
remedies.  Consult  a  special- 
ist on  the  subject. 


*  The  author  has  taken  the  liberty  of  altering  this  table  somewhat  from  the  original. 

The  subject  of  the  scientific  treatment  of  bad  feed-waters  is  a 
large  and  complex  one,  and  the  practical  application  of  the  proper 
methods  is  rather  recent  in  this  country.  Those  who  are  further 
interested  in  this  matter  should  consult  the  paper  of  Messrs.  Hunt 
and  Clapp,  from  which  the  above  summary  is  taken,  and  also  Mr. 
Albert  A.  Gary's  paper  on  Corrosion  and  Scale  from  Feed-waters,  in 
the  Engineering  Magazine  for  March,  April,  May,  and  June,  1897. 
Accounts,  of  the  use  of  petroleum  for  preventing  incrustation  will  be 


526  STEAM-BOILER  ECONOMY. 

found  in  Trans.  Am.  Soc.  M.  E.,  vols.  ix.  and  xi.,  a  statement  of  the 
method  of  purification  used  by  the  Solvay  Process  Company,  Syracuse, 
N.  Y.,  in  vol.  xiii.  p.  255,  and  a  description  of  the  method  used  on 
the  line  of  the  Southern  Pacific  Railway  in  a  paper  by  Mr.  Howard 
Stillman,  in  vol.  xix.  p.  415. 

Boiler  Compounds.— W.  M.  Booth  (Eng.  News,  July  27,  1905), 
gives  the  analyses  of  several  boiler  compounds  which  he  has  examined. 
One,  a  white  powder,  was  composed  of  soda  ash  with  a  little  free 
tannic  acid.  Another,  a  black  liquid,  contained  mainly  caustic  soda 
in  excess,  logwood,  tannin,  sugar,  sulphate  of  soda  and  a  small 
quantity  of  gum.  Its  use  was  prohibited.  A  third  contained  catechu, 
caustic  soda  and  tan  liquor.  These  liquids  were  sold  for  about  50 
cts.  per  gallon  and  cost  less  than  6  cts,  to  make.  Mr.  Booth  says : 

"We  have  two  materials  the  use  of  which  in  boilers  is  not  pro- 
hibited through  action  upon  the  metal  itself  or  on  account  of  price. 
If  prescribed  as  per  analysis,  in  slight  excess,  there  should  be  no 
injurious  results  through  their  use.  There  is  a  great  deal  of  fraud 
in  connection  with  boiler  compounds  generally.  A  better  class  of 
vendors  advertise  to  build  a  special  compound  for  a  special  water. 
The  less  scientific  members  of  the  boiler  compound  guild  carefully 
consign  each  sample  of  water  to  the  sewer  and  send  the  regular 
goods.  Others  have  a  stock  analysis  which  is  sent  to  customers  of 
a  given  locality  whether  it  contains  iron,  lime,  or  magnesium  sul- 
phates or  carbonates. 

"For  plants  of  from  75  to  150  H.P.,  24-hour  settling  tanks 
will  answer  the  purpose  of  a  softening  system.  Two  tanks,  each 
capable  of  holding  a  day's  supply  and  furnished  above  with  lime 
and  soda  tanks  in  common,  and  provided  with  sludge  valves  below, 
may  be  used  for  this  purpose.  Paddles  in  each  tank  capable  of  thor- 
oughly stirring  the  contents  may  be  actuated  from  above.  Such  a 
system  has  an  advantage  over  a  continuous  system,  in  that  the  exact 
amount  of  chemical  solutions  required  for  softening  the  particular 
water  in  the  tank  can  be  applied.  For  some  variations  of  such  a 
system,  several  companies  have  secured  patents  and  are  doing  a  large 
business.  The  fundamental  principles  are  not  patentable,  and  have 
been  used  for  many  years. 

The  Use  of  Boiler  Compounds.*  To  the  majority  of  steam-users, 
anything  that  is  put  into  a  boiler  to  lessen  troubles  due  to  the  forma- 

*  From  an  article  by  Albert  A.  Gary  in  American  Machinist,  Dec.  7,  1899. 


BOILER  TROUBLES  AND  BOILER   USERS1   COMPLAINTS.    527 

tion  of  scale,  is  a  "boiler  compound,"  and  the  fact  that  these  various 
so-called  compounds  act  differently  in  their  endeavor  to  accomplish 
their  purpose  is  not  generally  understood.  Such  nostrums  may  be 
divided  into  three  classes : 

First — Those  attacking  the  scale-producing  material  chemically. 
These  act  as  reagents  and  combine  with  the  matter  precipitated  from 
the  feed-water,  forming  a  third  substance  different  from  either  the 
original  precipitated  solids  or  the  ''reagent/'  the  theory  being  that 
the  new  substance  will  not  form  into  a  hard,  resisting  scale,  and  there- 
fore can  be  more  easily  removed  by  blowing-off  or  by  the  cleaning 
tools  used  after  the  boiler  is  opened. 

Second — Those  acting  mechanically  upon  the  precipitated  crystals 
of  scale-making  mattei  soon  after  they  are  formed.  Such  "com- 
pounds" are  of  a  glutinous,  starchy  or  oily  nature,  and  become  attached 
to  the  surface  of  the  newly  formed  crystals  (precipitated  from  the 
water)  surrounding  them,  as  the  skin  does  an  orange;  and  when  these 
crystals  fall  together  they  are  thus  robbed  of  their  cement-like  action, 
which  frequently  occurs  when  they  are  allowed  to  come  in  immediate 
contact. 

Third — Those  acting  both  mechanically  (as  just  described)  and 
also  as  a  solvent,  the  latter  action  partially  dissolving  scale  already 
formed,  and  by  this  "rotting"  effect  (as  it  is  often  called)  preparing 
the  scale  for  easy  removal. 

The  "compounds"  under  the  first  division  (which  act  chemically 
upon  the  scale-forming  matter)  also  frequently  accomplish  this  same 
rotting  effect  upon  scale  formed  previous  to  their  use.  Still  other 
divisions  or  sub-divisions  might  possibly  be  made,  but  the  above  will 
suffice  for  a  good  general  idea  of  the  subject. 

Taking  up  our  first  division  of  this  subject,  we  find  that  the 
principal  ingredients  used  in  such  "compounds"  are  soda  ash  (or 
carbonate  of  soda)  and  tannin  matters,  while  we  sometimes  find  caustic 
soda,  sal  soda,  acetic  acid,  and  numerous  other  active  agents  which 
are  generally  less  efficient  in  their  action  on  the  scale-forming  matter 
and  more  harmful  to  the  boiler  and  its  fittings. 

In  order  to  disguise  these  very  cheap  chemicals  and  help  the 
"compound"  vender  get  big  prices  for  his  powder  or  liquid,  whichever 
it  may  be,  there  are  often  added  other  substances  which  generally 
render  the  active  agents  less  efficient,  and  they  frequently  fall  un- 
changed to  the  bottom  of  the  boiler  with  the  scale,  thus  increasing 
the  deposit  and  aggravating  the  trouble. 

Such  added  substances  include  clay,  chalk,  sand,  etc.,  and  some- 
times coloring  matter  is  used  to  disguise  the  original  chemicals,  such 
as  tobacco- juice,  iron  scraps,  lampblack,  spent  tan,  etc. 

The  principal  scale-making  impurities  precipitated  in  boilers  are 
carbonate  of  lime  (CaC03),  carbonate  of  magnesium  (MgC03).  sul- 
phate of  lime  (CaS04)  and  sulphate  of  magnesium  (MgS04),  and 
although  there  are  generally  other  precipitates,  notice  of  these  alone 
will  be  sufficient  for  the  present  consideration. 


528  STEAM-BOILER  ECONOMY. 

The  chemical  action  taking  place  when  some  of  the  above-named 
active  agents  are  used  may  be  traced  as  follows : 

Soda  ash  is  a  dry  impure  carbonate  of  soda,  from  which  the  pure 
alkali  is  afterwards  made. 

The  carbonate  of  soda  (Na2C03)  is  used  to  act  upon  the  sulphate 
of  lime  and  magnesia,  as  shown  in  the  following  chemical  formulae : 

Sulphate  ,        Carbonate      'f__.n  •     Carbonate  ,       Sulphate 

(a)    of  Lime        and          of  Soda  form          of  Lime  and        of  Soda. 

CaSO4  +          Na2CO3  CaCO3  +  Na2SO4 

Sulphate  ,         Carbonate      t  Carbonate  •,       Sulphate 

(6)    Magnesium  and  of  Soda         form          Magnesia         and        of  Soda. 

MgS04          +          Na2C03  MgC03  +         Na2SO4 

Both  the  carbonate  of  lime  and  carbonate  of  magnesia  are  held  in 
solution  through  the  presence  of  carbonic  acid  gas  dissolved  in  the 
water,  which  unites  with  them  and  changes  the  monocarbonates  into 
bicar Donates  (which  are  only  known  to  exist  in  solution),  as  shown 
thus: 

Carbonate          ,   Carbonic         ,     TXr  ,         /•  Bicarbonate         Generally 

of  Lime       and      Acid         and     Water     form  of  Lime  Expressed 

CaOCOa       +        CO2          +        H2O         =.       CaO(CO2)2H2O  =  CaH2(CO3)2 

In  a  similar  manner  the  bicarbonate  of  magnesium  is  formed 
from  the  monocarbonate  thus : 

Carbonate  of       i  Carbonic       A    ^T  ,  ,.  Bicarbonate          Generally 

Magnesium    and      Acid      and    Water       form     of  Magnesium,      Expressed 
MgOCO.       +        CO2       +        H2O  =      MgO(CO2)2H2O  =  MgH2(CO3)2 

The  monocarbonates  (or  single  carbonates)  of  lime  and  magnesia 
are  but  slightly  soluble  in  water,  whereas  the  bicarbonates  (or  double 
carbonates)  are  very  soluble  in  cold  water,  and  this  fact  will  account 
for  the  presence  of  the  large  quantities  of  lime  and  magnesia  in  boiler 
waters  as  carbonates. 

When  waters  containing  the  bicarbonates  are  heated,  the  rise  in 
temperature  drives  off  the  extra  carbonic  acid  gas  and  leaves  behind 
the  practically  insoluble  monocarbonates,  which  are  precipitated. 

When  a  temperature  of  180°  Fahr.  is  reached,  a  considerable  per- 
centage of  the  bicarbonates  is  precipitated  (as  insoluble  monocar- 
bonates), and  at  290°  Fahr.  (a  temperature  corresponding  to  43  Ibs. 
gage-pressure)  the  precipitation  is  nearly  completed,  after  a  thorough 
boiling. 

Scale  forming  from  the  monocarbonate  of  lime  is  seldom  very 
troublesome,  if  not  allowed  to  accumulate  in  too  large  a  quantity,  nor 
allowed  to  remain  in  the  boiler  for  a  long  time;  while  the  precipi- 
tated monocarbonate  of  magnesia  gives  slightly  more  trouble,  due 
to  the  fact  that  it  seldom  is  found  in  scale  as  a  monocarbonate.  All 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.    529 

the  contained  carbonic  acid  (C02)  is  generally  lost  from  the  bicar- 
bonate of  magnesia  (MgO(C02)2H20)  by  the  time  it  forms  a  crust, 
leaving  behind  the  hydrate  of  magnesia  (MgO  +  H20  =  Mg02H2), 
which,  acts  as  a  cement  and  binds  closely  together  (though  not  very 
strongly)  whatever  precipitated  matter  it  may  come  in  contact  with. 

This  hydrate  of  magnesia  is  very  fine  and  light  when  precipitated 
and  requires  a  comparatively  long  time  to  settle. 

The  sulphates  of  lime  and  magnesia  are  very  soluble,  dissolving  in 
water  direct,  without  requiring  the  presence  of  carbonic  acid  or  any 
other  foreign  agent. 

The  amount  of  sulphate  of  lime  which  can  be  dissolved  in  one 
United  States  gallon  of  water  at  different  temperatures  may  be  ap- 
preciated by  examining  the  following  table : 

At  32°  Fahr.,  120  grains  per  gallon. 
At  95°  Fahr.,  148  grains  per  gallon. 
At  212°  Fahr.,  127  grains  per  gallon. 
At  250°  Fahr.,  9  grains  per  gallon. 
At  from  260°  to  302°  Fahr.,  it  is  practically  insoluble. 

This  latter  temperature  (302°)  corresponds  to  55  Ibs.  gage-pres- 
sure, and,  therefore,  when  water  is  thoroughly  boiled  at  this  tempera- 
ture, practically  all  of  the  sulphates  will  be  precipitated.  The 
crystals  of  sulphate  of  lime  will  be  found  to  be  long  and  needle-like, 
and  also  very  heavy  and  possessing  cement-like  qualities,  so  they  fall 
rapidly,  and,  mixing  with  the  precipitated  carbonates,  they  bind  them 
together  into  a  hard,  resisting  mass,  difficult  to  remove  with  even 
hammer  and  chisel,  if  they  form  a  considerable  proportion  of  the 
scale. 

It  is  here  where  the  active  agent  in  the  compound  is  supposed  to 
take  effect,  and  by  referring  to  the  reaction  given  above — in  the 
formulae  (a)  and  (b) — when  the  carbonate  of  soda  is  used,  it  will  be 
seen  that  the  sulphates  of  lime  and  magnesia  are  changed  into  car- 
bonates, which  are  precipitated  and  form  a  scale  varying  from  a  more 
or  less  porous,  friable  crust  to  a  "mush"  or  mud.  The  sulphate  of 
soda,  which  is  also  formed  by  this  reaction,  is  extremely  soluble,  re- 
maining in  solution  at  nearly  all  boiler  temperatures  and  forming  no 
scale,  unless  allowed  to  concentrate,  and  this  is  prevented  by  "blow- 
ing-off"  occasionally. 

The  tannin  matters,  referred  to  above,  are  obtained  from  various 
vegetable  sources  containing  tannic  acid,  such  as  certain  kinds  of 
sumach,  gallnuts,  catechu  (or  cutch)  bark,  etc.  Tannin  is  generally 
combined  with  soda  to  form  the  tannate  of  soda  for  use  with  boiler 
waters  to  keep  the  deposit  soft  or  in  suspension.  Its  action  is  supposed 
to  be  as  follows : 

The  tannate  of  soda  decomposes  the  carbonates  of  lime  and  mag- 
nesia as  they  enter  the  boiler,  and  tannates  of  lime  and  magnesia  are 


530  STEAM-BOILER  ECONOMY. 

precipitated  in  a  light,  flocculent,  amorphous  form  and  are  long  kept 
in  suspension  by  the  circulating  currents  of  water,  until  they  finally 
are  deposited  in  a  loose,  mushy  mass  in  that  part  of  the  boiler  where 
the  circulating  currents  are  the  weakest,  or  possibly  in  the  mud-drum. 

When  the  above  reaction  takes  place  the  carbonate  of  soda  is 
formed,  which  reacts  with  any  sulphates  that  may  be  present,,  as  has 
already  been  described. 

The  use  of  tannic  acid  in  the  boiler  cannot  be  recommended  un- 
reservedly, as  it  will  attack  the  iron  as  well  as  the  carbonates  (al- 
though, of  course,  more  slowly),  and  anything  that  will  corrode  the 
boiler  itself  certainly  cannot  be  desirable.  To  test  this,  any  one  can 
obtain  a  few  cents'  worth  of  tannic  acid  from  the  druggist,  and  by 
dissolving  the  crystals  in  a  glass  of  water  and  adding  some  iron 
filings  a  very  fair  quality  of  ink  can  be  made,  due  to  the  action  of  this 
acid  on  the  iron. 

In  practice,  the  reaction  of  caustic  soda  (Na202H2)  with  the  sul- 
phates seems  to  be  more  active  than  when  the  carbonate  of  soda  is 
used,  the  probable  reaction  being  as  shown  thus  : 

Sulphate   „    »  Carbonic  „    i  Caustic  ,.  „     Caustic  „    ,  Carbonic  n*  Sulphate 
of  Lime    and      Acid      and     Soda      form  Lime      and       Acid      andofSoda. 
CaSO4       +        CO,        +    2NaOH    =     CaH2O2    +        CO2        +    Na2SO 

The  carbonic  acid  used  in  this  formula  results  from  the  precipita- 
tion of  the  monocarbonates  from  the  bicarbonates,  as  has  been  ex- 
plained. 

The  secondary  reaction  from  the  result  just  arrived  at  is  as  follows  : 


Water- 

CaH2O2      +          CO2  =         CaOCO2       +        H2O 

The  use  of  caustic  soda  may  be  considered  less  desirable  than  the 
use  of  the  carbonate  of  soda  for  several  reasons. 

In  the  first  place,  if  present  in  excess,  it  will  cause  violent  foaming 
in  the  boiler,  and  with  this  foam  often  the  light  precipitated  matter 
in  the  boiler  will  be  carried  along  steam-pipes  into  valve-seats,  gage- 
glasses,  etc.  It  will  also  attack  and  cause  corrosion  of  the  brass  fit- 
tings, and  it  is  also  dangerous  to  handle,  owing  to  its  caustic  qualities, 
burning  the  flesh  painfully  wherever  it  comes  in  contact. 

An  excess  of  carbonate  of  soda  may  also  cause  foaming  in  the 
boiler,  but  not  as  violent  as  when  caustic  soda  is  used. 

Sal  ammoniac  (ammonium  chloride,  NH3HC1)  is  most  undesirable 
for  use  in  a  boiler,  due  to  the  liberation  of  hydrochloric  acid  (HC1) 
following  its  introduction  into  the  boiler.  This  acid  leaves  the  boiler 
in  a  Taporous  form,  with  the  steam,  corroding  the  boiler,  piping,  and 
nearly  everything  it  comes  in  contact  with. 

There  are  other  "compounds"  falling  under  this  classification,  of 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    531 

known  chemical  composition,  which  are  more  satisfactory  than  those 
named  above,  such  as  bisodium  phosphate  and  trisodium  phosphate, 
the  latter  being  obtainable  in  both  a  hydrous  and  anhydrous  state.  The 
latter  is  less  bulky  and  its  reaction  with  the  sulphate  of  lime  is  shown 
by  the  following  formula : 

2  Parts  3  Parts 

Trisodium  ,  Sulphate  f             Phosphate  3  Parts 

Phosphate  and  of  Lime  form         of  Lime  and       Sulphate  of  Soda. 

2Na3PO4  f  3CaSO4         =           Ca3(PO4)2  +  3Na2SO4 

The  phosphate  of  lime,  after  this  reaction,  falls,  forming  a  slushy 
mud,  making  at  the  most  a  very  weak  crust,  while  the  sulphate  of  soda 
remains  in  solution,  as  previously  described. 

The  second  division  of  compounds  includes  a  class  of  materials 
which  are  gradually  falling  into  disuse,  due  to  their  proved  undesira- 
bility.  They  thicken  and  foul  the  water  in  the  boiler  and  coat  its 
surfaces  with  non-conducting  material,  and  occasionally  the  precipi- 
tated scale-making  matter,  along  with  this  class  of  compound,  will 
obstruct  the  passage  of  heat  through  the  boiler-plates,  so  as  to  cause 
bagging  and  burning. 

In  this  class  we  find  slippery  elm,  ground  bones,  horns  and  hoofs, 
potatoes,  dextrine,  and  starch,  animal  fats  and  animal  or  vegetable 
table  oils. 

As  rapidly  as  the  scale-forming  crystals  are  precipitated  from  the 
feed-water,  they  fall  into  this  sticky  fluid  and  become  coated  with  its 
filth,  and  they  finally  fall  to  the  place  of  deposit,  where  they  remain 
in  a  mushy,  separated  state  until  the  organic  matter  chances  to  be 
burned  out,  when  they  will  form  into  a  loose,  friable  scale. 

A  surface  blow-off  or  skimming  device  is  most  essential  to  reduce 
the  evil,  when  this  class  of  compound  is  used,  and  the  bottom  blow-off 
cock  should  also  be  opened  very  frequently. 

The  principal  substances  used  for  the  third  class  of  compounds 
are  petroleum  and  kerosene. 

Petroleum  oil  has  much  more  of  the  enveloping  quality  described 
under  the  last  (or  third)  classification  than  the  kerosene.  Besides 
producing  this  effect  on  the  scale-matter,  both  have  an  active  rotting 
effect  on  the  scale  already  formed,  the  kerosene  in  this  case  being 
superior  to  the  petroleum. 

Crude  oil  should  never  be  used,  but  a  carefully  refined  oil,  which 
has  been  deprived  of  its  tar  or  wax,  should  be  selected  for  this  pur- 
pose, as  these  cause  the  formation  of  a  tough,  impervious  scale  pro- 
ductive of  bagged  sheets  and  collapsed  flues.  Petroleum  or  kerosene 
should  be  fed  to  the  boiler  with  the  feed-water,  drop  by  drop,  through 
a  sight-feed  apparatus  similar  to  those  used  to  feed  oil  to  the  cylinders 
of  engines.  Under  no  consideration  should  large  amounts  of  these 
oils  be  fed  to  a  boiler  at  one  time,  as  it  must  be  remembered  that  the 
more  volatile  portion  of  the  petroleum  will  be  quickly  distilled  off  in 


532  STEAM-BOILER  ECONOMY. 

the  hot  boiler,  leaving  the  least  efficient  portion  behind,  while  the 
more  volatile  kerosene  will  be  vaporized  very  quickly,  before  it  has 
time  to  thoroughly  mix  with  the  water. 

Where  hard  scale  has  formed  in  a  boiler,  it  is  most  effectually 
treated  by  giving  it  a  coat  of  petroleum  or  kerosene,  to  partially  dis- 
solve or  rot  it.  This  may  be  applied  with  a  brush  or  squirted  on,  but 
an  easier  method  of  application  is  to  first  fill  the  boiler  with  water 
above  the  line  of  scale-deposit  and  then  pour  the  oil  on  the  surface  of 
this  water  and  let  the  water  gradually  run  out  of  the  bottom  of  the 
boiler,  thus  leaving  the  oil  behind  clinging  to  the  whole  interior 
surface.* 

As  stated  above,  kerosene  is  the  most  effective  in  destroying  the 
tenacity  or  coherence  of  this  deposited  scale,  but  this  method  of  using 
either  oil  is  not  without  attending  danger,  on  account  of  the  explo- 
siveness  of  the  vapor  given  off;  so  great  care  must  be  taken  to  have 
no  lights  in  the  vicinity  of  the  boiler  under  such  treatment,  as  men 
have  been  seriously  injured  by  this  lack  of  prudence. 

The  treatment  of  feed-waters  inside  of  the  boiler  has  been  a  prac- 
tice of  many  years'  standing,  but  in  the  light  of  recent  progress  is  not 
to  be  commended.  A  boiler  certainly  has  all  that  it  can  reasonably  be 
expected  to  do  when  it  is  generating  steam  without  being  called  upon 
to  perform  the  functions  of  a  chemical  laboratory. 

Mr.  H.  E.  Smith,  chemist  of  the  Chicago,  Milwaukee  &  St.  Paul 
Ry.  Co.,  in  a  letter  to  the  author,  June,  1902,  writes  as  follows  con- 
cerning the  chemical  action  of  soda-ash  on  the  scale-forming  substances 
in  boiler  waters: 

Soda-ash  acts  on  carbonates  of  lime  and  magnesia  in  boiler  water 
in  the  following  manner:  The  carbonates  are  held  in  solution  by 
means  of  the  carbonic  acid  gas  also  present,  which  probably  forms 
bicarbonates  of  lime  and  magnesia.  Any  means  which  will  expel 
or  absorb  this  carbonic  acid  will  cause  the  precipitation  of  the  car- 
bonates. One  of  these  means  is  soda  ash  (carbonate  of  soda),  which 
absorbs  the  gas  with  the  formation  of  bicarbonate  of  soda.  This  method 
would  not  be  practicable  for  softening  cold  water,  but  it  serves  in  a 
boiler.  The  carbonates  precipitated  in  this  manner  are  in  flocculent 
condition  instead  of  semi-crystalline  as  when  thrown  down  by  heat. 
In  practice  it  is  desirable  and  sufficient  to  precipitate  only  a  portion 
of  the  lime  and  magnesia  in  flocculent  condition.  As  to  equations, 
the  following  represent  what  occurs : 

*  An  effective  method  of  cleaning  a  boiler  which  has  become  heavily  coated 
with  hard  sulphate  of  lime  scale  is  to  put  in  it  a  large  quantity  of  caustic  soda, 
say  50  Ibs.  for  a  large  boiler,  and  boil  it  at  atmospheric  pressure,  the  safety  valve 
being  opened,  for  several  hours.  This  converts  the  hard  scale  into  a  soft  sub- 
stance which  may  be  removed  by  a  scraper,  followed  by  thorough  washing  with 
cold  water.— W.  K. 


BOILER   TROUBLES  AND  BOILER   USERS'   COMPLAINTS.    533 

Ca(HCO3)2 -f-NazCOj  =  CaCO3 +2NaHCO3. 
Mg(HCO3)2  +Na2CO3  =  MgCO3+2NaHCO3. 
(free)  CO2+Na2CO3+ H2O    =2NaHCO3. 

Chemical  equivalents :  —  106  pounds  of  pure  carbonate  of  soda — 
equal  to  about  109  pounds  of  commercial  58  degree  soda-ash — are 
chemically  equivalent  to — i.  e.,  react  exactly  with — the  following 
weights  of  the  substances  named:  Calcium  sulphate,  136  Ibs. ;  mag- 
nesium sulphate,  120  Ibs.;  calcium  carbonate,  100  Ibs.;  magnesium 
carbonate,  84  Ibs.;  calcium  chloride,  111  Ibs.;  magnesium  chloride, 
95  Ibs. 

Such  numbers  are  simply  the  molecular  weights  of  the  substances 
reduced  to  a  common  basis  with  regard  to  the  valence  of  the  com- 
ponent atoms. 

Important  work  in  this  line  should  not  be  undertaken  by  an  ama- 
teur. "Kecipes"  have  a  certain  field  of  usefulness,  but  will  not  cover 
the  whole  subject.  In  water  purification,  as  in  a  problem  of  mechanical 
engineering,  methods  and  apparatus  must  be  adapted  to  the  conditions 
presented.  Not  only  must  the  character  of  the  raw  water  be  con- 
sidered, but  also  the  conditions  of  purification  and  use. 

Use  of  Kerosene  to  Remove  Scale. — The  Locomotive,  July,  1898, 
comments  on  the  use  of  kerosene  for  the  removal  of  scale  as  follows : 

We  are  of  the  opinion  that  the  introduction  of  the  oil  daily, 
mixed  with  the  feed  water,  is  not  the  most  effective  method  of  using 
oil  for  the  removal  of  scale  that  has  already  formed.  We  believe  that 
much  better  results  would  be  obtained  as  follows :  The  boiler  is  thor- 
oughly dried  out  so  as  to  remove  all  moisture  from  the  scale.  This 
is  accomplished  by  opening  the  manhole  and  handholes,  as  soon  as 
the  boiler  is  blown  down.  When  the  boiler  is  cooled  down  sufficiently 
to  be  entered  for  examination  and  cleaning,  the  scale  will  then  become 
dry.  All  sediment  and  loose  fragments  should  then  be  brushed  out, 
and  kerosene  oil  sprayed  over  the  plates  and  tubes,  so  as  to  saturate 
the  scale  thoroughly.  The  oil  which  accumulates  in  the  bottom  of 
the  boiler  will  rise  on  the  surface  of  the  water  when  the  boiler  is  filled, 
and  be  brought  in  contact  with  such  parts  of  the  tubes  as  may  not 
be  reached  by  the  direct  spray.  Oil  so  applied  will  penetrate  the 
scale  and  loosen  it  from  the  iron.  The  boiler  should  then  be  opened 
in  a  week  or  two,  and  all  loose  scale  be  removed.  It  is  important  to 
attend  to  this  part  of  the  operation,  as  otherwise  there  is  great  danger 
of  the  loose  scale  collecting  upon  the  fire  sheets,  and  causing  them 
to  burn  or  bulge.  In  tubular  boilers  it  is  often  necessary  to  break 
down  the  scale  lodged  between  the  tubes.  In  water-tube  boilers  it 
is  necessary  to  dry  out  as  above  described,  uncap  the  tubes,  and  then, 
with  a  mop  saturated  in  kerosene,  brush  through  the  tubes  until  the 
scale  is  saturated.  If  the  boiler  is  allowed  to  stand  for  24  hours, 
a  scraper  will  remove  considerable  scale  on  which  it  would  have  no 


534 


STEAM-BOILER  ECONOMY. 


effect  previous  to  the  saturation  of  the  scale  with  kerosene.  Opening 
and  scraping  the  tubes  after  running  the  boiler  for  a  week  will  remove 
much  larger  quantities.  The  thorough  drying  of  the  boilers  is  im- 
portant, when  this  method  is  used,  since  oil  will  not  penetrate  wet 
scale.  Open  lights  should  not  be  used  in  or  about  the  boiler  when 
applying  kerosene  oil  as  above  described. 

Graphite  as  a  Scale  Preventive. — Finely  ground  flake  graphite 
has  been  used  with  good  effect  in  the  removal  of  old  scale  from  boilers 
and  in  preventing  the  adhesion  of  new  scale  to  the  plates.  Its  action 
is  not  chemical,  but  mechanical.  The  fine  particles  work  their  way 
into  the  minute  cracks  in  the  old  scale  and  gradually  penetrate  be- 
tween the  scale  and  the  metal.  The  manufacturers  (Dixon  Crucible 
Co.)  say  that  if  the  scale  is  very  hard  and  thick  it  may  take  three 
or  four  months  for  the  graphite  to  loosen  it,  but  once  removed,  scale 
can  never  adhere  firmly  to  the  metal  as  long  as  the  graphite  treat- 
ment is  continued.  The  graphite  becomes  thoroughly  intermixed 
with  new  scale  as  it  forms,  rendering  it  soft  and  crumbly. 

The  simplest  way  of  feeding  graphite  into  a  boiler  is  to  introduce 
it  into  the  pump  suction  line  by  means  of  a  funnel  and  valve  such 
as  are  shown  in  Fig.  239.  A  pint  of  graphite  is  mixed  in  a  pail  of 
as  are  shown  in  Fig.  239.  A  pint  of  graphite 
is  mixed  in  a  pail  of  water  and  poured  into 
the  funnel  while  the  valve  is  closed.  When 
the  valve  is  opened  the  mixture  will  be  drawn 
into  the  pump.  It  is  recommended  that  about 
one  pint  of  graphite  be  fed  into  each  boiler 
every  twelve  hours,  with  an  extra  one-third  pint 
for  every  100  H.P.  above  250  H.P.  When  the 
old  scale  has  been  removed  the  amount  should 
be  reduced  slightly. 

A  correspondent  of  Power,  November  12, 
1912,  writes  that  he  used  graphite  with  excellent 
effect  as  long  as  the  boilers  were  using  a 

certain  feed-water,  but  when  the  water  was  changed  the  boilers  scaled 
heavily  and  graphite  only  seemed  to  make  the  scale  harder.  "With 
graphite  as  with  other  compounds/'  he  says,  "what  will  give  good 
results  in  one  plant  may  be  detrimental  in  another."  Another  cor- 
respondent says:  "Graphite  is  not  a  substance  that  can  be  used 
carelessly.  Unless  proper  care  is  taken  to  keep  the  blow-off  pipe  clear 
and  means  taken  to  remove  the  loosened  scale  its  use  is  dangerous/' 


FIG.  239.— FUNNEL 
FOR  GRAPHITE. 


BOILER  TROUBLES  AND  BOILER    USERS'  COMPLAINTS.       535 

Water-softening  Apparatus,  (From  the  Report  of  the  Committee 
on  Water  Service,  of  the  Am.  Railway  Eng'g  and  Maintenance  of  Way 
Assn.,  Eng.  Rec.,  April  20,  1907. — Between  three  and  four  hours  is 
necessary  for  reaction  and  precipitation.  Water  taken  from  running 
streams  in  winter  should  have  at  least  four  hours'  time.  At  least 
three  feet  of  the  bottom  of  each  settling  tank  should  be  reserved  for 
the  accumulation  of  the  precipitates. 

An  article  on  "The  Present  Status  of  Water  Softening/'  by  G.  C. 
Whipple,  in  Cassier's  Mag.,  Mar.,  1907,  illustrates  several  different 
forms  of  water-purifying  apparatus.  A  classification  of  degrees  of  hard- 
ness corresponding  to  parts  of  carbonates  and  sulphates  of  lime  and 
magnesia  per  million  parts  of  water  is  given  as  follows.:  Very  soft, 
0  to  10  parts;  soft,  10  to  20;  slightly  hard,  25  to  50;  hard,  50  to  100; 
very  hard,  100  to  200;  excessively  hard,  200  to  500;  mineral  water, 
500  or  more.  The  same  article  gives  the  following  figures  showing 
the  quantity  of  chemicals  required  for  the  various  constituents  of 
hard  water.  For  each  part  per  million  of  the  substances  mentioned 
it  is  necessary  to  add  the  stated  number  of  pounds  of  lime  and  soda 
per  million  gallons  of  water. 


For  Each  Part  per  Million  of 

Pounds  per  Million  Gallons. 

Lime. 

Soda. 

Free  CO2 

10.62 

4.77 
4.67 
0.00 
19.48 

0 
9.03 
0 

8.85 
0 

Free  acid  (calculated  as  H2SO4) 

Alkalinity 

Incrustants  .  .          ....        ...... 

Magnesium  

The  above  figures  do  not  take  into  account  any  impurities  in  the 
chemicals.  These  have  to  be  considered  in  actual  operation. 

An  illustrated  description  of  a  water-purifying  plant  on  the  Chicago 
&  Northwestern  Ry.  by  G.  M.  Davidson  is  found  in  Eng.  News, 
April  2,  1903.  Two  precipitation  tanks  are  used,  each  30  ft.  diam., 
16  ft.  high,  or  70,000  gallons  each.  As  some  water  is  left  with 
the  sludge  in  the  bottom  after  each  emptying,  their  net  capacity 
is  about  60,000  gallons  each.  The  time  required  for  filling,  pre- 
cipitating, settling  and  transferring  the  clear  water  to  supply 
tanks  is  12  hours.  Once  a  month  the  sludge  is  removed,  and  it  is 
found  to  make  a  good  whitewash.  Lime  and  soda-ash,  in  predeter- 
mined quantity,  as  found  by  analysis  of  the  water,  are  used  as  pre- 
cipitants.  The  table  on  top  of  p.  536  shows  the  effect  of  treatment  of 
well  water  at  Council  Bluffs,  Iowa. 

The  minimum  amount  of  scaling  matter  which  will  justify  treat- 
ment cannot  be  stated  in  terms  of  analysis  alone,  but  should  be  stated 
in  terms  of  pounds  incrusting  matter  held  in  solution  in  a  day's 
supply.  Besides  the  scale-forming  solids,  nearly  all  water  contains 


536 


STEAM-BOILER  ECONOMY. 


Before 
Treatment. 

After 
Treatment. 

Total  solid  matter,  grains  per  gallon  

53  67 

31  35 

Carbonates  of  lime  and  magnesia  

.     25.57 

3  14 

Sulphates  of  lime  and  magnesia  

19.55 

Silica  and  oxides  of  iron  and  aluminum 

1  76 

0  40 

Total  incrusting  solids 

46  88 

3  54 

Alkali  chlorides 

1  21 

1  27 

Alkali  sulphates  

5  58 

26  32 

Total  non-incrusting  solids  

6  79 

27  81 

Pounds  scale-forming  matter  in  1000  gals  

6.69 

0  51 

more  or  less  free  carbonic  acid.  Sulphuric  acid  is  also  found,  par- 
ticularly in  streams  adjacent  to  coal  mines.  Serious  trouble  from 
corrosion  will  result  from  a  small  amount  of  this  acid.  In  treating 
waters,  the  acids  can  be  neutralized,  and  the  incrusting  matter  can 
be  reduced  to  at  least  5  grains  per  gallon  in  most  cases. 


QUANTITY  OF  PURE  REAGENTS  REQUIRED  TO  REMOVE  ONE  POUND  OF  INCRUSTING 
OR   CORROSIVE    MATTER   FROM    THE    WATER. 


Incrusting  or  Corrosive 
Substance  Held  in 
Solution. 

Amount  of  Reagent.      (Pure.) 

Foaming 
Matter. 
Increased. 

Sulphuric  acid          

0  57  Ib.  lime  plus  1  .08  Ibs.  soda  ash.  .  .  . 

1  45  Ibs. 

Free  carbonic  acid.    .    .  . 

1  27  Ibs.  lime  

None 

Calcium  carbonate.    .    .  . 

0  56  Ib.  lime  

None 

Calcium  sulphate  

0  78  Ib.  soda  ash  

04  Ibs. 

Calcium  chloride        .  . 

0  96  Ib.  soda  ash  ...    

.05  Ibs. 

Calcium  nitrate             .  . 

0  65  Ib.  soda  ash    

04  Ibs. 

Magnesium  carbonate.  .  . 
Magnesium  sulphate.  .  .  . 
Magnesium  chloride.  .  .  . 
Magnesium  nitrate  

Calcium  carbonate 

1  .  33  Ibs.  lime  
0.47  Ib.  lime  plus  0.88  Ib.  soda  ash.  ... 
0.59  Ib.  lime  plus  1.11  Ibs.  soda  ash  .  .  . 
0.38  Ib.  lime  plus  0.72  Ib.  soda  ash.  ... 

1  71  Ibs.  barium  hydrate            

None 
.  18  Ibs. 
.22  Ibs. 
.  15  Ibs. 

None 

M[agnesium  carbonate 

4  05  Ibs.  barium  hydrate            

None 

IVlagnesium  sulphate 

1  42  Ibs.  barium  hydrate  .           

None 

Calcium  sulphate* 

1  26  Ibs  barium  hydrate            .  .      .    . 

None 

*  In  precipitating  the  calcium  sulphate  there  would  also  be  precipitated  0.74  Ib.  of  calcium 
carbonate  or  0.31  Ib.  of  magnesium  carbonate,  the  1.26  Ibs.  of  barium  hydrate  performing 
the  work  of  0.41  Ib.  of  lime  and  0.78  Ib.  of  soda*ash,  or  for  reacting  on  either  magnesium  or 
calcium  sulphate,  1  Ib.  of  barium  hydrate  performs  the  work  of  0.33  Ib.  of  lime  plus  0.62  Ib. 
of.  soda  ash;  and  the  lime  treatment  can  be  correspondingly  reduced. 

Barium  hydrate  has  no  advantage  over  lime  as  a  reagent  to  precip- 
itate the  carbonates  of  lime  and  magnesia  and  should  not  be  considered 
except  in  connection  with  the  treating  of  water  containing  calcium 
sulphate. 

Method  of  Testing  Boiler  Waters. — A.  J.  Boardman,  in  Power, 
March  3,  1909,  describes  the  method  of  testing  water  before  and  after 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.     537 

softening  by  means  of  soda-ash  and  lime,  used  in  an  8400  H.P.  boiler 
plant  in  Indianapolis.  The  analysis  of  the  river  water  showed  a 
total  of  25.3  grains  of  scale  forming  and  suspended  matter  per  U.  S. 
gallon,  the  incrusting  solids  being  15.69  grains  per  gallon  or  2.24 
pounds  per  1000  gallons.  Before  the  treatment  was  adopted  different 
boiler  compounds  had  been  used,  at  an  average  cost  of  $270  per 
month,  with  very  little  decrease  in  the  amount  of  scale,  and  from  15 
to  64  boiler  tubes  were  burned  out  in  a  month.  With  the  new  treat- 
ment, costing  $104  per  month,  the  maximum  number  of  tubes  re- 
placed in  a  month  was  only  two.  An  abstract  of  Mr.  Boardman's 
paper  follows : 

It  was  decided  to  treat  the  water  by  using  soda  ash  and  lime  to 
throw  down  the  scale-forming  matter,  and  to  check  this  treatment 
with  feed-water  analysis. 

The  expenditure  for  a  testing  outfit  was  not  over  $10.  The  appa- 
ratus consisted  of  two  50-cc.  burettes,  one  square  pint  bottle  with 
rubber  cork,  one  pint  standard  N/50  HC1  solution,  one  pint  standard 
soap  solution,  three  500-cc.  beakers,  one  funnel,  100  filter  papers 
No.  2,  one  100-cc.  phenolphthalein  indicator,  one  100-cc.  methyl  orange 
indicator,  one  100-cc.  graduated  test  tube,  10  ounces  barium  chloride, 
stirring  rod,  burette  support,  stand,  -etc.  It  is  necessary  to  have  HC1 
exactly  correct.  Formal  HC1  is  98.7  per  cent  hydrochloric  acid. 

Hard  water  may  be  defined  as  water  containing  in  solution  mineral 
compounds  that  curdle  or  precipitate  soap ;  generally  the  salts  of  lime, 
magnesia,  iron,  etc.  In  the  United  States  hardness  is  generally  stated 
as  parts  of  calcium  carbonate  per  million,  i.  e.,  the  number  of  parts 
by  weight  of  CaCo3  that  would  have  to  be  added  to  a  million  parts  by 
weight  of  water  to  produce  the  specified  degree  of  hardness.  To 
convert  grains  per  gallon  to  parts  per  million  multiply  by  17.14.  The 
standard  soap  solution  is  obtained  by  dissolving  pure  castile  soap  in 
alcohol. 

Total  Hardness. — In  testing  for  total  hardness  in  river  water, 
25  cc.  of  the  water  is  diluted  with  75  cc.  of  distilled  water.  This  is 
titrated  with  the  standard  soap  solution  in  a  square  pint  bottle 
provided  with  a  rubber  stopper.  One  cc.  of  soap  solution  is  added 
at  a  time  until  there  is  some  evidence  of  a  permanent  lather.  Then 
add  y2  cc.  and  decrease  to  %  cc.  at  a  time  until  the  lather  is  per- 
manent,-when  the  bottle  can  be  laid  on  its  side  for  three  minutes 
with  no  decrease  in  the  lather.  The  bottle  must  be  well  shaken  after 
each  addition  of  soap  solution.  In  Clark's  Table  of  Hardness*  oppo- 
site the  number  of  cubic  centimeters  of  soap  solution  used  will  be 
found  the  degree  of  hardness  in  parts  per  million. 

*  Gill's  "Engine  Room  Chemistry,"  p.  105;  also  M.  E.  Pocket-book,  8th  Ed., 
p.  694. 


538  STEAM-BOILER  ECONOMY. 

Permanent  Hardness. — This  is  obtained  by  subtracting  the  degree 
of  temporary  hardness,  that  due  to  the  bicarbonates,  and  lessening  by 
boiling,  from  the  total  hardness.  The  result  is  expressed  as  before 
in  parts  of  calcium  carbonate  per  million  parts  of  water. 

Temporary  Hardness. — Each  cubic  centimeter  of  the  test  solution 
used  indicates  0.001  of  a  gram  of  CaC03  per  million.  In  using,  pro- 
ceed as  follows:  Dilute  25  cc.  of  raw  water  with  75  cc.  of  distilled 
water  and  add  five  drops  of  methyl  orange  indicator,  which  will  turn 
the  solution  a  yellowish  tinge.  Now  add  the  acid  solution  drop  by 
drop  until  the  color  of  the  solution  turns  from  a  yellowish  to  a  rose 
pink.  The  number  of  cc.  of  the  HC1  solution  used  multiplied  by  4 
will  be  the  temporary  hardness  expressed  as  calcium  carbonate  in  parts 
per  million. 

Analysis  of  Softened  Water. — Measure  out  100  cc.  of  the  purified 
water,  put  it  into  a  beaker  and  add  a  few  crystals  of  barium  chloride. 
The  addition  of  four  drops  of  phenolphthalein  indicator  will  turn  the 
solution  purple  if  there  is  plenty  of  lime  present.  Now  add  standard 
acid  solution  drop  by  drop  to  obtain  a  clear  solution.  This  is  analysis 
for  lime.  The  number  of  cubic  centimeters  of  acid  solution  added 
indicates  the  amount  of  lime  present,  as  explained  above,  and  may  be 
read  off  directly  from  the  graduation  on  the  burette.  Measure  out 
another  100  cc.  of  the  softened  water,  add  four  drops  of  the  phenol- 
phthalein solution  and  titrate  with  the  standard  acid  solution  to  obtain 
a  clear  solution  as  before.  Call  the  result  in  the  first  operation  B 
and  the  result  in  the  second  operation  A.  Then  A  minus  B  in  cubic 
centimeters  multiplied  by  0.091  equals  the  number  of  pounds  of  soda 
ash  required  for  1000  gallons;  B  multiplied  by  0.048  equals  the  num- 
ber of  pounds  of  lime  per  1000  gallons. 

Methods  for  Purification  of  Water.* — The  more  or  less  complete 
removal  of  scale-forming  matter  or  the  neutralization  of  corrosive 
substances  which  occur  in  boiler  feed-water  has  been  carried  out  by 
several  methods  in  the  United  States. 

The  methods  may  be  classified  as  follows : 

I.     MECHANICAL    METHODS. 

These  include  feed-water  heaters,  scum-catchers  and  blow-off  cocks. 

II.    CHEMICAL    METHODS. 

(a)  Direct  Method. — The  chemicals  are  placed  in  the  boiler  or 
run  into  it  with  the  water  supply. 

(b)  Indirect  Method. — The  chemicals  are  fed  into  the  water  on 
its  way  to  a  storage  tank  which  serves  also  for  the  completion  of 
chemical  reaction  and  for  sedimentation. 

*  Abstract  of  a  paper  by  J.  O.  Handy,  read  before  the  International  Con- 
,  St.  Louis,  October  3  to  8,  1904.    Elec.  Renew,  Nov.  12,  1904. 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.      539 

(c)  Intermittent  Method. — The  chemical  treatment  is  given  al- 
ternately to  the  contents  of  two  tanks,  allowing  reaction  and  sedi- 
mentation to  take  place  during  periods  of  quiet.  Partially  clarified 
water  is  drawn  off  through  filters  and  repumped  to  storage  tanks. 

(d)  Continuous  Method. — The  chemical  treatment  is  given  auto- 
matically to  the  water  as  it  enters  the  apparatus.  The  chemical  re- 
action, sedimentation  and  clarification  take  place  simultaneously  or 
successively  during  the  progress  of  the  water  through  the  apparatus. 

CLASS   I MECHANICAL  METHODS. 

Feed-water  heaters  remove  more  or  less  completely  from  water  the 
carbonate  of  lime  which  it  contains,  but  more  important  scale-forming 
substances  are  not  affected  and  pass  on  into  the  boiler,  from  which 
it  is  impossible  to  remove  them  except  very  imperfectly  by  scum- 
catchers  or  blow-off  cocks. 

Sulphate  of  lime  deposits  as  scale  in  boilers  very  gradually  with 
increasing  concentration.  Pressure  and  temperature  have  a  modify- 
ing influence  on  the  rate  of  deposition,  but  no  temperature  is  reached 
in  steam  boiler  practice  at  which  sulphate  of  lime  immediately  falls 
out  of  solution. 

CLASS    II CHEMICAL    METHODS. 

2  a — Direct  Method. — This  practice  is  very  general  in  the  United 
States  and  the  beneficial  results  obtained  have  been  in  exact  relation 
to  the  judgment  shown  in  selecting  the  chemicals  and.  the  care  shown 
in  carrying  out  the  details  of  the  treatment.  Soda  ash  has  been 
most  widely  employed.  Used  without  discrimination,  it  is  rarely 
beneficial. 

The  experience  of  the  Chicago,  Milwaukee  and  St.  Paul  Eailway 
proved  conclusively  that  the  systematic  use  of  soda  ash,  combined 
with  regular  blowing  off  of  the  sludge  produced  by  chemical  action, 
was  a  measure  of  great  economic  importance. 

Principle :  "When  waters  are  treated  in  the  boiler  with  soda  ash, 
the  incrusting  solids  are  changed  to  carbonates  and  precipitated  as 
a  soft  sludge  which  is  readily  blown  out,  instead  of  coming  down  in 
a  crystalline  condition  and  adhering  to  the  boiler." 

AMOUNT   OF   SODA   ASH    USED 
For  Each  Grain  per  Gallon.  ggf  Ashjer 

Calcium  carbonate 0. 02  Ib. 

Magnesium  carbonate 0 .02  ' ' 

Calcium  sulphate .- 0. 10  " 

Magnesium  sulphate 0 . 13  ' ' 

Magnesium  chloride 0. 16  ' ' 

Limitations  of  Direct  Soda-ash  Treatment. — Boilers  must  be  more 
frequently  washed  out,  because  blowing-off  does  not  completely  remove 


540  STEAM-BOILER  ECONOMY. 

sludge.  Foaming  occurs  frequently,  due  partly  to  suspended  sludge 
and  partly  to  the  presence  of  carbonate  of  soda  in  variable  excess  in 
the  water.  Very  hard  water  cannot  be  treated  sufficiently  to  prevent 
scale  formation  without  introducing  soda  enough  to  cause  foaming. 

Aside  from  its  price,  which  is  about  four  times  that  of  soda  ash, 
phosphate  of  soda  has  certain  advantages.  It  produces  by  its  action 
on  the  lime  salts  in  the  water,  flocculent,  amorphous  precipitates  which 
are  absolutely  non-adherent  to  boiler  surfaces  and  are  easily  blown 
out. 

Limitations  of  Tri-sodium  Phosphate. — The  price,  taken  together 
with  its  high  combining  weight,  makes  it  at  least  nine  times  as 
expensive  as  soda  ash  for  water-softening  purposes.  It  cannot  be 
used  for  complete  softening  of  cold  water  because  the  chemical  reactions 
are  not  finished  in  any  reasonable  time  without  heat.  Magnesia 
precipitates  very  slowly.  The  precipitate  is  bulky  and  an  apparatus 
with  unusual  sludge  room  would  be  required. 

Lime  and  Soda  Ash. — In  the  treatment  of  acid  waters  from  coal 
mines  and  washers,  some  large  steam  users  have  kept  their  boiler 
water  supply  neutral  by  means  of  milk  of  lime  fed  proportionately 
through  feed  pumps.  Others  have  used  soda  ash  alone.  The  best 
practice  for  acid  waters  is  the  use  of  lime  and  soda  ash  in  equivalent 
amounts. 

The  lime  treatment  leaves  sulphate  of  lime,  a  scale-forming 
substance,  in  the  water.  The  soda-ash  treatment  leaves  free  carbonic 
acid  in  the  water  and  the  iron  salts  are  incompletely  removed  in 
consequence.  Foaming  is  also  encouraged  by  the  carbonic  acid  gas. 
No  by-products  of  injurious  nature  are  formed  when  dilute  caustic 
soda,  or  lime  +  soda  ash  are  used  for  acid  waters. 

Of  all  the  chemicals  available  for  direct  treatment  of  boiler  feed 
water,  sodium  phosphate  is  best  and  soda  ash  and  lime  next.  Any 
direct  treatment  should  be  regarded  merely  as  a  temporary  expedient 
to  be  superseded  by  softening  machines  as  soon  as  conditions  permit. 

2  b — Indirect  Method. — Treatment  of  water  by  the  introduction 
of  chemicals  into  the  water  as  it  flows  to  the  storage  tank  was  the 
first  step  in  the  evolution  from  direct  treatment  toward  complete 
softening  machines.  This  method  has  no  feature  to  recommend  it 
except  low  first  cost.  In  their  simplest,  crudest  form,  the  plants 
consist  of: 

1.  An  arrangement  for  supplying  chemical  solution  at  approxi- 
mately the  required  rate  from  a  barred  attached  to  the  suction  of  the 
supply  pump. 

2.  A  floating  draw-off  in  the  service  so  that  approximately  clear 
water  may  be  drawn  from  it. 

3.  A  dump  valve  in  the  bottom  of  the  service  tank  for  sludge 
removal. 

Having  usually  only  an  imperfect  chemical  proportioning  device, 
no  arrangement  for  ensuring  steady  progression  of  water  through  the 
storage  tank,  and  no  provision  for  drawing  off  more  than  part  of  the 


BOILER   TROUBLES   AND  BOILER  USERS'  COMPLAINTS.     541 

sludge  without  emptying  the  tank,  such  plants  do  only  imperfect 
work. 

2  c — Intermittent  Method. — The  devices  under  this  heading"  are 
intermittent  in  operation  in  that  there  is  a  pause  of  several  hours 
after  treatment.  This  is  to  give  the  time  considered  necessary  for 
chemical  reaction  and  sedimentation. 

In  the  commercial  development  of  the  intermittent  system  of 
water  softening,  N.  0.  Goldsmith,  of  Cincinnati,,  Ohio,  and  J.  B. 
Greer,  of  Pittsburgh,  Pa.,  have  done  important  work.  Many  of  their 
plants  have  been  installed  in  the  United  States  and  the  systems  are 
styled,  respectively,  the  "We-Fu-Go"  and  the  "Ideal."  Their  work 
dates  principally  from  the  year  1896. 

They  added  to  previous  practice  in  the  country  the  following 
points. 

The  use  of  milk  of  lime  instead  of  lime  water. 

The  use  of  sand  filters  to  clarify  the  softened  water. 

The  "We-Fu-Go"  plants  have  paddle  stirrers,  while  the  "Ideal" 
plants  use  compressed  air  for  mixing  and  agitating  purposes.  There 
are  no  other  essential  differences. 

The  general  plan  of  operation  is  as  follows : 

Two  tanks  are  provided,  the  aggregate  capacity  of  which  is 
usually  eight  times  the  hourly  output  expected.  These  may  be  of 
either  wood  or  iron  construction  and  may  be  placed  on  ground  level 
or  elevated  on  trestle-work  according  to  whether  repumping  of  soft- 
ened water  is  to  be  allowed  for  or  avoided. 

The  tanks  are  filled  alternately  to  a  certain  level  with  hard  water. 
In  some  plants  the  milk  of  lime  is  added  during  the  filling  and  the 
agitator  is  run  at  the  same  time.  In  most  of  the  plants,  the  Arch- 
butt-Deeley  practice  of  dissolving  the  soda  ash  in  the  milk  of  lime 
and  adding  both  together  when  the  tank  is  filled,  is  the  one  followed. 

Agitation  continues  for  fifteen  to  twenty  minutes,  followed  by  a 
period  of  perfect  rest  usually  approximating  four  hours. 

At  the  end  of  this  time  the  softened  water  is  drawn  off  from  near 
the  surface  through  floating  discharge  pipes.  It  passes  through  sand 
or  crushed  quartz  filters  to  storage  tanks  from  which  it  is  repumped 
to  a  higher  elevation  if  necessary. 

Intermitting  Softening  Plants  for  Hot  Water. — Almost  all  chemi- 
cal relations  are  hastened  by  the  application  of  heat.  A  hot  water 
plant  can  be  operated  with  smaller  tanks  than  a  cold  water  one. 

The  Solvay  Process  Company's  Purifying  System. — Onondaga  lake 
water  is  used.  The  water  is  hard  and  saline. 

Parts  per 
100,000 

Calcium  bicarbonate 14 . 38 

Magnesium  bicarbonate 1 . 32 

Calcium  sulphate 22 . 88 

Calcium  chloride 4 . 90 

Magnesium  chloride 72 . 27 

3pdium  chloride 97.90 


542  STEAM-BOILER  ECONOMY. 

Sodium  carbonate  (soda  ash)  is  the  purifying  agent  used,  25  per 
cent  in  excess  of  the  calculated  amount  being  placed  in  each  of  two 
4300-gallon  tanks  before  the  water  enters.  The  water  is  at  178°  F. 
(having  been  used  in  condensers).  It  enters  the  tanks  at  the  rate 
of  13,000  gallons  per  hour,  which  means  that  three  tanks  are  filled 
and  emptied  hourly,  making  the  cycle  for  one  tank  twenty  minutes. 

This  plant  is  interesting  because  of  the  small  tankage  and  the 
high  rate  of  purification.  The  reaction-tank  area  is  only  two-thirds 
of  the  hourly  output,  and  there  are  no  mechanical  devices  to  facilitate 
mixing  or  hastening  the  mechanical  reaction.  The  high  temperature 
of  the  water  to  be  treated  and  the  fact  that  25  per  cent  excess  soda  ash 
is  used,  explains  the  success  of  the  process.  The  treated  water  is 
pumped  through  sand  filters  into  the  boilers.  Seven  filters,  from  four 
to  six  feet  in  diameter  by  four  to  five  feet  high  are  used. 

After  passing  the.  filters  the  water  contains  lime  salts  equivalent 
to  2.50  parts  sulphate  of  lime  per  100,000.  The  boiler  tubes  show 
a  dust-like  coating,  easily  rubbed  off.  By  blowing  off  at  intervals 
the  concentration  of  sulphate  of  soda,  carbonate  of  soda  and  salt  is 
kept  at  or  below  2°  Baume  (hydrometer).  One  man  on  each  eight- 
hour  shift  attends  to  the  treatment. 

2  d — Continuous  Method. — The  type  of  machine  referred  to  is 
one  so  designed  that  the  flow  of  water  to  the  plant  operates  all  neces- 
sary mechanism  (stirrer,  etc.).  The  feed  of  chemicals  is  regulated 
by  proportioning  devices.  Proper  mixing  of  chemicals  with  hot 
water  takes  place  automatically  and  the  water  passes  evenly  through 
the  machine,  while  the  chemical  reaction  of  softening  proceeds  and 
sedimentation  is  almost  perfectly  effected.  A  filter  at  the  top  of  the 
machine  gives  final  clarification  and  the  softening  water  is  discharged 
without  repumping  into  the  storage  tank. 

Desrumeaux  utilized  by  means  of  a  water-wheel  the  power  of  the 
water  flowing  into  the  softening  machine  for  driving  a  stirrer  in  his 
lime  tank.  In  both  lime-water  and  reaction  tanks,  he  had  annular, 
spiral  passageways  for  the  rising  water,  aiming  to  give  it  a  steady, 
curcuitous  upward  movement.  Sludge  settling  on  the  spiral  plates 
was  supposed  to  slide  to  outlets  properly  placed  to  favor  undisturbed 
fall  to  the  base  of  the  machine.  The  feed  for  chemicals  was  controlled 
by  valves  operated  by  floats  in  the  hard-water  box. 

The  design  has  been  modified  by  Mr.  C.  H.  Koyl.  The  spiral 
settling  device  was  discarded;  the  small  lime-water  tank  was  replaced 
by  a  very  large  one,  and  elaborate  stirrers  were  placed  in  the  reaction 
tank. 

The  lime-water  tank  is  made  large  so  that  it  will  produce  prac- 
tically clear  saturated  lime  water  of  definite  strength  and  not  milk 
of  lime.  The  rate  of  clarification  varies  according  to  whether  hard 
water  or  soft  water  is  used  for  making  lime  water. 

Stirring  always  assists  chemical  reaction,  but  machines  with  no 
stirring  beyond  about  five  minutes'  mixing  turn  out  properly  softened 
water.  The  course  of  the  water  through  the  apparatus  as  effected 


BOILER   TROUBLES  AND  BOILER   USERS'  COMPLAINTS.    543 

by  its  internal  design  is  a  very  important  factor  in  determining  the 
completion  of  reaction  and  sedimentation. 

The  Kennicott  water  softener  differs  in  the  following  respects 
from  other  continuous  softeners:  1,  the  chemical  feed-proportioning 
device;  2,  the  use  of  soft  water  for  lime  water;  3,  method  of  mixing 
chemicals  and  hard  water;  4,  means  of  assisting  sedimentation;  5, 
compact,  concentric  tank  arrangement. 

The  proportioning  devices  -employed  in  connection  with  continu- 
ous chemical  feed  in  the  several  softening  machines  used  in  this 
country  are:  1,  Weirs;  2,  stopper  valve  actuated  by  tipping-bucket; 
3,  pumps  actuated  by  tipping-bucket;  4,  spoons  actuated  by  tipping- 
bucket;  5,  fixed  orifices  for  discharge;  6,  movable  and  adjustable 
orifices  for  discharge. 

Continuous  Systems  for  Hot  Water. — Any  system  or  plant  which 
fulfils  the  conditions  for  softening  cold  water  will  necessarily  soften 
hot  water.  Steel  construction  is  best  and  smaller  tanks  may  be  used. 
Nevertheless,  it  is  a  mistake  to  sacrifice  anything  in  thoroughness  of 
mixture  or  means  of  securing  uniformity  of  progress  of  water  through 
the  apparatus. 

The  typical  continuous  hot-water  plant  consists  simply  of:  (a), 
soda  and  lime-water  tanks;  (6),  separate  feed  pumps;  (c),  mixing 
tank  with  baffle  partitions;  (d),  sand  filter. 

The  chemical  feed  pump  may  be  coupled  up  with  the  hard-water 
feed  pump,  but  in  many  cases  this  is  not  done  and  the  only  means 
given  the  operator  to  judge  of  accuracy  of  feed  is  a  bottle  of  phenol- 
phthalein  solution.  As  this  reagent  gives  a  pink  color  as  soon  as  the 
free  carbonic  acid  in  the  water  has  been  neutralized,  it  does  not 
indicate  whether  lime  enough  has  been  added  to  decompose  bicar- 
bonates  and  soda  enough  for  other  lime  and  magnesia  salts. 

Hot  water  softening  had  best  be  carried  out  with  an  apparatus 
having  more  reliable  chemical  feed  devices  than  proportional  pumps. 

The  Economic  Results  of  Water  Softening. — The  considerations 
which  lead  to  the  taking  up  of  water  softening  by  steam  users  may 
be  grouped  as  follows :  • 

First. — Loss  of  service  of  boilers,  due  to  impossibility  of  satis- 
factory continuous  operation  with  hard  water. 

Second'. — Possibility  of  substantial  savings  in  fuel  and  repair  bills 
and  the  checking  of  rapid  deterioration  of  boilers. 

The  charges  against  a  water  softening  installation  are: 

Interest  on  cost  of  plant. 

Depreciation. 

Chemicals  for  softening. 

Attendance. 

Power  for  operation   (and  repumping). 

The  credit  items  for  a  softener  are: 
Fuel  saving. 
Repair  saving. 


544  STEAM-BOILER  ECONOMY. 

Depreciation  saving. 

Increased  service  obtainable  from  steam  generators. 

Cost  of  Softening  Plants. — The  best  softening  plants  with  steel 
construction  cost  from  $4  to  $5  per  H.P.  for  installations  up  to  1000 
H.P;  for  1000  to  2000  H.P.,  $4  to  $3;  2000  to  5000  H.P.,  $3  to  $2; 
5000  to  15,000  H.P.,  $2  to  $1.20  per  horsepower. 

Cost  of  Chemicals. — Much  of  the  building  lime  is  so  high  in  mag- 
nesia as  to  make  it  unfit  or  uneconomical  to  use.  From  90  to  95% 
lime  can  be  had  and  should  be  insisted  upon. 

The  cheapest  waters  to  soften  are  those  the  hardness  of  which  is 
due  to  carbonates  of  lime  and  magnesia  only.  Such  waters  require 
simply  lime-water  treatment.  It  costs  only  0.2  cent  per  1000  gallons 
to  remove  1.42  pounds  of  carbonate  of  lime  (equivalent  to  ten  grains 
per  gallon)  and  only  0.48  cent  to  remove  the  same  quantity  of  carbon- 
ate of  magnesia.  These  amounts  are  sufficient  to  give  a  great  deal 
of  trouble  in  heaters  and  boilers. 

The  removal  of  sulphates  and  other  soluble  compounds  of  lime 
and  magnesia  from  water  requires  the  use  of  soda  ash.  It  costs  1.20 
cents  per  1000  gallons  to  remove  sulphate  of  lime  equivalent  to  ten 
grains  per  United  States  gallon.  The  same  amount  of  sulphate  of 
magnesia  requires  1.36  pounds  of  soda  ash  which  costs  1.36  cents 
per  1000  gallons. 

The  cost  of  chemicals  for  softening  water  varies  from  0.5  cent  to 
5  cents  per  1000  gallons,  averaging  from  1  to  2  cents. 

The  cost  of  attendance  at  softening  plants  varies  greatly.  With 
the  best  type  of  plants  two  or  three  hours  per  day  are  all  that  are 
required  for  attendance  unless  the  installation  is  very  large.  Chemical 
tests  for  control  of  the  softening  plant  can  be  carried  out  by  persons 
of  average  intelligence.  The  best  plants  have  all  stirrers  or  other 
mechanism  actuated  by  water  power.  The  flow  of  water  to  be  softened 
starts  everything, 

The  Permutit  Water-softening;  Process. — "Permutit"  is  the  name 
given  to  a  porous  mineral  compound  obtained  by  fusing  together 
felspar,  kaolin,  sand  and  soda.  This  substance  placed  in  an  ordinary 
iron  tank  removes  the  hardness  by  exchanging,  as  the  water  passes 
through  it,  the  lime  and  magnesia,  which  cause  the  hardening,  for 
an  equal  amount  of  sodium. 

All  that  is  required,  after  the  tank  has  been  set'  up,  is  that  the 
crystals  be  placed  in  the  tank  and  the  water  turned  on.  Because  of 
the  chemical  change  which  occurs  by  the  exchange  of  sodium  for 
magnesium  and  lime,  the  compound  has  to  be  regenerated  when  the 
sodium  becomes  exhausted.  When  this  exhaustion  occurs,  the  re- 
generation is  accomplished  by  running  a  solution  of  common  salt 
through  the  "permutit."  This  done,  the  filter  is  ready  for  work 


BOILER   TROUBLES  AND  BOILER   USERS'  COMPLAINTS.    545 

again,  as  good  as  new.    The  cost  of  maintenance  is  only  the  price  of 
common  salt. 

Permutit  is  an  artificial  sodium  zeolite  of  the  formula  2Si02, 
A1203,  Na20,  6H20.  The  reactions  with  lime  carbonate  and  sul- 
phate, the  permutit  being  designated  by  P,  are 

PNa2  +  CaH2(CO3)2  =  PCa  +  2NaHCO3. 

PNa2  +  CaSO4  =  PCa  +  Na2SO4. 
The  regenerating  reaction  is  as  follows: 

PCa  +  2NaCl  =  PNa2  +  CaCl2. 

The  filtering  apparatus  may  be  either  of  the  open  or  of  the  closed 
type.  In  either  type,  the  charge  of  permutit  rests  on  a  bed  of  crushed 
flint,  and  a  similar  bed  of  flint,  carried  on  a  perforated  plate,  is 
placed  in  the  upper  part  of  the  filter  to  prevent  the  escape  of  per- 
mutit during  the  regenerative  process.  The  depth  of  the  charge  is 
determined  by  the  hardness  of  the  water  and  the  speed  of  softening 
required.  Hard  water  may  be  perfectly  softened  by  passing  it  'through 
a  layer  of  permutit  24  to  40  inches  in  depth  at  a  rate  of  10  to  16 
feet  an  hour,  and  the  speed  of  filtration  usually  adopted  lies  between 
these  limits.  The  permissible  speed  of  filtration  can  be  raised  by 
increasing  the  depth  of  permutit  charge,  but  it  is  limited  by  the  fact 
that  for  efficient  action  the  water  must  have  time  to  penetrate  the 
interior  of  the  grains.  The  extreme  limits  of  speed  are :  For  water 
containing  0.01  per  cent  lime,  approximately  27  feet;  0.02  per  cent., 
16  feet;  and  0.03  per  cent,  10  feet  an  hour.  The  volume  of  water 
treated  depends,  of  course,  on  the  area  of  the  charge. 

The  regenerating  solution  generally  used  contains  about  10  per 
cent  of  sodium  chloride,  and  to  facilitate  the  action  the  solution  is 
usually  heated  to  100°  to  120°  F. 

Admission  of  the  solution  to  the  filter  is  regulated  automatically 
at  a  very  slow  rate  to  permit  the  solution  thoroughly  to  penetrate  the 
grains  of  permutit.  Admission  occupies  4  to  5  hours,  and  when  the 
charge  is  completely  impregnated  the  solution  is  left  in  the  filter 
for  about  the  same  period.  The  charge  is  then  drained  and  washed 
thoroughly  to  remove  all  traces  of  salt.  Since  the  regenerative  process 
is  completed  in  about  8  hours,  where  continuous  service  is  required 
two  filters  are  necessary  for  alternate  purification  and  regeneration. 

The  sole  precaution  necessary  is  that  the  concentration  of  the  soda 


546 


STEAM-BOILER  ECONOMY. 


salts  in  the  boiler  shall  not  exceed  2.5  to  3  per  cent.     (From  circulars 
of  The  Permutit  Co.,  New  York.) 

The  Eureka  Water-softening  Apparatus,  made  by  the  Dodge  Man- 
ufacturing Co.,  is  shown  in  Fig.  240.  It  consists  essentially  of  two 
portions,  the  smaller  a  lime-saturating  tank,  and  the  larger  a  decant- 
ing tank,  for  precipitation  of  the  scale-forming  constituents  after 
being  acted  upon  by  the  lime  solution  and  reagents.  The  water  to 

be  treated  enters  the  top  tank 
B  and  is  divided  for  delivery, 
a  small  portion  to  the  satura- 
tor  J ,  the  greater  portion  to 
the  decanting  tank.  On  its  way 
to  the  decanting  tank,  the 
water  passes  over  a  wheel  E, 
whose  rotation  actuates  stirrer 
arms  in  the  saturator.  The 
saturator  J  provides  a  continu- 
ous supply  of  saturated  lime 
solution,  which  is  fed  with 
other  reagents  in  proper  pro- 
portions, under  automatic  con- 
trol, from  a  small  tank  G  into 
the  central  tank  M  of  the  de- 
canter. 'Here  the  reaction  takes 
place,  the  water  passing  down- 
ward and  returning  upward  in 
the  main  body  of  the  large 
tank,  passing  spirally  among 
the  slant-settling  plates  N. 
On  these  spiral  surfaces  the 
scale-forming  matters  and 
other  impurities  are  deposited 
in  flakes  which  gravitate  freely 
to  the  conical  bottom  of  the 
FIG.  240,  main  tank,  whence  they  may 

be  passed  off  into  the  sewer  by 

occasional  opening  of  the  valve  8.  Any  sediment  forming  at  the 
bottom  of  the  lime  saturator  tank  may  similarly  be  blown  off  through 
the  valve  U.  The  water  itself,  continuing  upward,  passes  through 
filtering  material  A  into  an  annular  space,  whence  it  is  drawn  off  as 
wanted.  The  water  is  treated  cold  by  means  of  reagents  which  may 
be  bought  in  market  at  a  trifling  cost.  All  the  attention  required  is 
to  renew  daily  the  lime  and  other  reagents  in  prescribed  proportions 
and  to  flush  out  the  accumulated  slush  by  opening  the  valves  8  and  U. 

External  Corrosion  is  a  frequent  cause  of  dangerous  weakening  of 
a  steam-boiler.  It  is  most  commonly  due  to  dampness,  and  is  there- 


BOILER  TROUBLES  AND  BOILER  USERS'  COMPLAINTS.     547 

fore  more  liable  to  take  place  when  a  boiler  is  out  of  service  and  cold 
than  when  it  is  in  use  and  constantly  kept  hot.  The  most  active 
agent  of  corrosion  is  sulphurous  acid  gas,  produced  from  the  sulphur 
in  the  coal,  which  is  converted  into  sulphuric  acid  in  the  presence  of 
moisture  in  the  cold.  Mud-drums  and  other  parts  of  a  boiler  which 
are  farthest  removed  from  the  fire,  and  on  which  there  is  apt  to  be 
an  accumulation  of  damp  soot  or  dirt,  are  especially  subject  to  ex- 
ternal corrosion.  The  precautions  to  be  taken  to  prevent  this  kind 
of  corrosion  are  to  have  the  boiler  frequently  inspected  and  to  keep 
it  clean,  dry,  and  hot. 

The  Life  of  a  Steam-boiler. — What  is  known  as  the  "life"  of  a 
boiler  generally  depends  upon  the  amount  of  corrosion  to  which  it  is 
subjected.  With  good  feed-water  which  will  neither  corrode  the 
metal  nor  cause  the  deposit  of  a  dangerous  scale,  and  with  care  to 
keep  the  outside  surface  perfectly  dry,  a  life  of  forty  years  for  a  boiler 
is  not  uncommon.  With  slow  corrosion  its  life  may  be  reduced  to 
five  years  or  less,  with  the  additional  inconvenience  that  the  pressure 
of  steam  which  may  be  safely  carried  is  continually  being  reduced 
during  its  life. 

Besides  corrosion  other  causes  tending  to  shorten  the  life  of  a 
boiler  are :  ( 1 )  Tendency  to  accumulaton  of  scale,  mud,  or  grease  on 
the  plates  over  or  near  to  the  fire,  causing  "bagging"  of  plates, 
leakage  of  seams,  and  sometimes  explosions.  (2)  Overheating  of 
riveted  seams  where  they  overlap,  especially  when  they  are  covered 
with  scale.  (3)  Hidden  defects,  due  to  strains  or  other  causes,  such 
as  those  described  below. 

Defects  Discovered  by  Inspection. — The  Locomotive,  published  by 
the  Hartford  Steam-boiler  Inspection  and  Insurance  Co.,  gives  the 
following  statement  showing  the  number  and  kind  of  defects  dis- 
covered by  the  inspectors  of  that  company  during  the  year  1912.  (See 
table  at  top  of  p.  548.) 

Explosions  Caiised  by  Hidden  Defects.— It  is  the  common  opinion 
that  explosions  are  due  to  carelessness  of  handling  by  the  firemen,  or 
to  negligence  of  inspectors  in  not  discovering  defects,  but  occasionally 
an  explosion  takes  place  which  is  not  due  to  either  of  these  causes. 
On  February  27,  1897,  a  disastrous  explosion  took  place  at  the 
Acushnet  Mills,  New  Bedford,  Mass.,  wrecking  a  portion  of  the  mills 
and  killing  and  injuring  several  persons.  The  boiler  that  exploded 
was  built  in  1890.  Examination  showed  that  the  break  was  almost 
identical  with  that  of  the  explosion  of  a  boiler  at  the  Langley  factory, 


548 


STEAM-BOILER  ECONOMY. 


Number  of  visits  of  inspection  made 183,519 

Total  number  of  boilers  examined 337,178 

Number  found  uninsurable 977 


Nature  of  Defects.' 

Whole 
Number. 

Dangerous. 

Cases  of  sediment  or  loose  scale  

26  2Q9 

1    KKQ 

Cases  of  adhering  scale  

40  336 

1  43fi 

Cases  of  grooving  

2  700 

2^2 

Cases  of  internal  corrosion  

15  403 

co^ 

Cases  of  external  corrosion  

10411 

8Q^ 

Cass  of  defective  bracing  

1  391 

331 

Cases  of  defective  staybolting  

1  712 

345 

Settings  defective  

8  119 

7AC 

Fractured  plates  and  heads   

3288 

510 

Burned  plates.          

4965 

^17 

Laminated  plates.                

445 

55 

Cases  of  defective  riveting     

1  816 

405 

Cases  of  leakage  around  tubes.    . 

10  159 

1  607 

Cases  of  defective  tubes  or  flues. 

11  488 

4  780 

Cases  of  leakage  at  seams  

5  304 

401 

Water-gages  defective.        

3  663 

816 

Blow-offs  defective  

4429 

1  398 

Cases  of  low  water.         

447 

151 

Safety-valves  overloaded      

1  349 

380 

Safety-valves  defective  

1  534 

419 

Pressure-gages  defective  

6  765 

568 

Boilers  without  pressure-gages  

633 

102 

Miscellaneous  defects  .        ... 

2268 

420 

Total               .      . 

164  924 

18932 

Fall  River,  Mass.,  in  June,  1895,  which  boiler  was  made  by  the  same 
builders  that  made  the  boiler  in  New  Bedford.  The  boiler  parted 
in  a  horizontal  seam  of  the  middle  sheet,  close  to  the  rivet-holes,  and 
under  the  lap,  and  the  fault  was  owing  to  a  crack  in  the  plates 


ILJ      \_)       w       v 

o    o  o 


o 


FIG.  241. — A  HIDDEN  CRACK. 

under  the  outer  edge  of  the  rivet-heads,  as  shown  in  the  accompanying 
cuts,  Figs.  241  and  242.  The  Locomotive,  speaking  of  this  class  of 
fractures,  says: 

Most  of  the  fractures  of  the  plate  are  undoubtedly  due  to  the 
bending  of  the  plates  in  the  rolls.  From  30  to  40  per  cent  of  the 
sectional  area  of  the  plate  is  removed  along  the  line  of  the  joint  by 


BOILER   TROUBLES  AND  BOILER  USERS'  COMPLAINTS.    549 

punching  or  drilling  the  rivet-holes;  and  when  the  part  that  is  thus 
weakened  is  passing  through  the  rolls,  the  curvature  of  the  plates  at 
this  point  is  sensibly  increased.  When  the  plates  thus  affected  are 
brought  into  position  for  riveting  they 
will  not  lie  closely,  but  have  to  be 
knocked  together  with  a  sledge,  or 


forced  together  hydrostatically,  before    "~  \     /  \     / 

the  rivets  can  be  driven.    This  means       FlQ  242._SECTION  OF  SEAM. 
that  there  is  a  severe  local  strain  left 

in  the  plates,  the  effects  of  which  are  likely  to  become  visible 
at  some  time  in  the  subsequent  history  of  the  boiler.  When  the 
joint  has  been  riveted  up,  the  parts  of  the  plate  that  lie  under 
the  heads  of  the  rivets  are  held  together  so  firmly  that  the  yield- 
ing action  that  occurs  in  every  boiler,  as  the  pressure  and  tem- 
perature vary,  will  not  be  felt  at  this  point,  but  will  be  transferred 
to  a  line  lying  at>  or  just  beyond,  the  edge  of  the  rivet-heads.  In  the 
course  of  time  these  slight  changes  of  form,  when  combined  with 
the  stress  already  existing  along  this  line  from  the  cause  just 
described,  are  likely  to  develop  a  crack  starting  from  the  inside 
surface  of  the  outer  plate,  at  a  place  completely  hidden  from 
view,  and  extending  insidiously  outward,  until  the  final  rupture 
of  the  plate  is  accomplished,  and  the  boiler  gives  way  in  a  violent 
explosion. 

Here  is  the  record  of  an  explosion  due  to  a  cause  that  had  been 
concealed  for  seven  "years,  and  which  cause  was  so  hidden  that  it  could 

not  be  found  by  either  external  or  in- 
ternal inspection. 

It  may  be  said  that  this  accident 

FIG.  243.-BUTT  AND  STRAP        and  that  at  the  LanSle?  mill>  in  1895> 
JOINT.  would  not  have  happened  if  the  boilers 

had   been  properly  made,   and   if  the 

riveted  joint  had  been  of  the  form  shown  in  Fig.  243,  but  it  must 
be  remembered  that  the  horizontal  tubular  boiler  is  favored  chiefly 
on  account  of  its  low  first  cost,  and  low  cost  is  generally  not  com- 
patible with  the  highest  excellence  of  material  and  workmanship. 
If  a  cheap  form  of  boiler  is  selected  and  the  contract  given  to  the 
lowest  bidder,  it  is  only  to  be  expected  that  cheap  material,  cheap 
workmanship,  and  unskilled  designers  are  likely  to  be  employed  in 
its  construction. 

The  water-  and  steam-drum  of  a  water-tube  boiler  being  much 
smaller  than  the  shell  of  a  fire-tube  boiler,  and  costing  a  much  smaller 
percentage  of  its  total  cost,  there  is  not  the  same  temptation  to  make 
the  drum  cheap  that  there  is  with  the  shell  boiler. 


550  STEAM-BOILER  ECONOMY. 

Causes  of  Boiler  Explosions.  (W.  H.  Boehm,  Power,  Oct.  8, 
1912). — Boiler  explosions  may  be  attributed  to  improper  construction, 
improper  installation,  or  incompetent  or  careless  operation. 

Improper  construction  may  consist:  of  unsuitable  or  inferior 
material;  poor  workmanship;  abuse  of  material,  as  when  unmatched 
rivet  holes  are  drift-pinned  to  place,  or  uncylindrical  shells  are 
sledged  to  form;  or  employing  the  more  dangerous  lap  joint  for  the 
side  seams  instead  of  the  more  safe  and  more  sensible  butt  joint. 

The  lap  joint  in  new  boilers  should  be  prohibited  by  law  in  all 
States,  as  it  now  is  in  some. 

Improper  installation  may  consist  of  so  supporting  the  boiler 
and  its  piping  as  to  allow  temperature  changes  to  set  up  dangerous 
stresses  in  the  material,  of  improperly  attaching  the  usual  appur- 
tenances such  as  safety  valves,  steam  and  water  gages,  check,  blow-off 
and  stop  valves. 

Incompetent  or  careless  operation  may  consist  in  allowing  the 
steam  gage  to. get  out  of  order,  in  allowing' the  water-gage  connections 
to  become  so  clogged  as  to  indicate  ample  water  when  there  is  none 
in  the  boiler,  in  allowing  the  safety  valve  to  become  so  stuck  to  its 
seat  as  to  fail  to  blow  at  the  pressure  for  which  it  was  set,  in  allowing 
grease  to  enter  or  scale  to  accumulate  in  the  boiler,  in  allowing  large 
quantities  of  cold  water  to  impinge  against  hot  plates,  in  allowing 
the  water  to  be  driven  from  the  heated  surfaces  by  forced  firing,  in 
allowing  a  large  valve  to  be  opened  too  suddenly,  in  allowing  two 
boilers  to  be  cut  in  on  the  same  steam  main  when  their  pressures 
are  unequal,  and  in  allowing  minor  repairs  to  be  neglected  until 
they  endanger  the  whole  structure. 

Many  violent  boiler  explosions  occur  either  just  prior  to  the 
starting  of  the  engines  in  the  morning,  or  while  they  are  idle  at  the 
noon  hour,  or  shortly  after  they  have  been  shut  down  for  the  day. 
One  reason  is  that  when  steam  is  not  being  drawn  from  the  boiler 
it  accumulates  rapidly ;  and  if  the  safety  valve  fails  to  relieve  the 
pressure,  explosion  soon  follows. 

The  rapidity  with  which  the  bursting  pressure  is  reached  may  be 
shown  as  follows: 

Let  T  =  time  in  minutes  required  to  reach  the  bursting  pressure; 
W  =  weight  of  water  in  the  boiler ; 
t  =  temperature  of  the  steam  at  bursting  pressure; 
t'  =  temperature  of  the  steam  at  normal  working  pressure; 
U  =  number  of  heat  units  per  minute  supplied  by  the  furnace 
and  absorbed  by  the  water. 

The  heat  balance  is  then  represented  by  the  equation: 

UT  =  w(t  -  o ;  T  =  7?  (*  -  *')• 


BOILER  TROUBLES  AND  BOILER  USERS'  COMPLAINTS.    551 

Take,  for  example  a  100  H.P.  boiler  containing  at  normal  level 
5000  Ibs.  of  water  and  suppose  it  uses  50,000  heat  units  per  minute 
when  evaporating  50  Ibs.  of  water  per  minute.  Then  if  the  normal 
gage  pressure  be  85  Ibs.,  the  corresponding  temperature  of  the  steam 
is  327  deg.,  and  if  the  bursting  gage  pressure  be  485  Ibs.  the  corres- 
ponding temperature  of  the  steam  is  467  deg. ;  and  the  time  required 
to  reach  the  bursting  pressure  with  all  steam  openings  closed  and  the 
safety  valve  stuck  is: 

-  327)  -  14  minutes. 

That  is,  with  a  stuck  safety  valve,  only  14  min.  would  elapse  from 
the  time  the  engines  were  shut  down  until  the  explosion  followed: 

If  the  fire  be  drawn  when  the  openings  are  closed,  ebullition 
ceases.  If  a  valve  be  opened,  ebullition  starts  again,  even  though 
there  still  be  no  fire  under  the  boiler. 

With  the  openings  closed  it  is  the  pressure  on  the  surface  of  the 
water  that  prevents  further  generation  of  steam.  If  a  small  rupture 
occurs  below  the  water  line  a  violent  explosion  may  not  ensue.  But 
if  a  large  outlet  above  the  water  line  be  suddenly  opened,  as,  for 
example,  when  a  steam  pipe  fails,  then  the  sudden  liberation  of  the 
pressure  on  the  surface  of  the  high-temperature  water  will  allow 
it  to  flash  suddenly  into  steam  and  cause  a  violent  explosion  and 
water-hammer  that  will  disrupt  the  strongest  possible  construction. 

Grease  in  Boilers. — Grease  does  not  dissolve  or  decompose  in  water, 
nor  does  it  remain  on  the  surface.  Heat  in  the  water  and  its  violent 
ebullition  causes  the  grease  to  form  in  sticky  drops  which  adhere  to 
and  varnish  the  metal  surfaces  of  the  boiler.  This  varnish  by  pre- 
venting the  water  from  coming  into  intimate  contact  with  the  metal, 
prevents  the  water  from  absorbing  the  heat,  and  this  causes  a  blister- 
ing or  burning  of  the  plate  that  often  results  in  a  serious  rupture, 
or  a  violent  explosion. 

Scale  in  Boilers. — If  scale  is  allowed  to  accumulate  to  any  con- 
siderable thickness  in  a  boiler,  a  bag  or  rupkire  of  the  shell  is 
inevitable,  unless  the  scale  happens  to  be  of  a  spongy  formation,  which 
is  not  often  the  case.  Just  why  this  is  so,  is  shown  by  the  following 
simple  experiment. 

Take  an  ordinary  granite  iron  or  tinned  iron  stewpan  and  firmly 
glue  to  its  underside  a  postage  stamp.  Pour  water  into  the  pan  and 
place  it  on  a  gas  stove  so  that  the  postage  stamp  will  be  in  direct 
contact  with  the  flame.  Leave  the  pan  on  the  stove  until  the  water 
has  boiled  violenty  and  then  examine  the  stamp.  The  stamp  will 
not  even  be  charred,  much  less  burned,  notwithstanding  that  it  was 
on  the  underside  of  the  pan  and  in  direct  contact  with  the  hottest 
part  of  the  flame. 

Now  put  into  the  pan  a  mixture  of  water  and  portland  cement 
half  an  inch  thick.  This,  when  set,  will  be  the  equivalent  of  half 


552  STEAM-BOILER  ECONOMY. 

an  inch  of  scale.     Repeat  the  experiment  made  before  and  it  will  be 
found  that  the  stamp  will  burn  up  very  quickly. 

The  reason  that  the  postage  stamp  is  not  charred  by  the  flame 
when  no  scale  is  present  is  that  the  water,  being  in  immediate  con- 
tact with  the  thin  bottom  of  the  vessel,  absorbs  the  heat  as  fast 
as  it  is  put  into  the  vessel  by  the  flame.  The  result  is  that,  no  matter 
how  hot  the  flame  may  be,  the  bottom  of  the  vessel  remains  at 
practically  the  same  temperature  as  the  boiling  water  with  which 
it  is  in  contact.  In  an  open  vessel  the  temperature  of  boiling  water, 
212  deg.,  this  is  not  sufficiently  high  to  char  paper.  When  scale 
is  present,  the  water  cannot  absorb  the  heat  as  fast  as  it  is  put  into 
the  vessel  by  the  flame,  and  as  a  result  the  temperature  becomes 
greater  than  212  deg.  and  burns  the  postage  stamp. 

It  is  the  same  with  steam  boilers.  If  the  water  comes  in  direct 
contact  with  the  thin  plates,  the  heat  is  absorbed,  the  temperature 
of  the  plates  remains  practically  the  same  as  the  water,  and  no 
harm  is  done.  If  there  be  a  considerable  thickness  of  impervious 
scale  in  the  boiler,  the  water  cannot  absorb  the  heat  as  fast  as  it  is 
put  into  the  plates  by  the  furnace,  and  so  the  plates  become  over- 
heated, get  red,  become  plastic,  and  finally  give  way  to  the  force  of 
steam  pressure,  causing  a  bag,  or  a  rupture,  or  a  violent  explosion. 

Scale  endangers  the  safety  of  boilers  in  other  ways.  It  clogs  the 
feed  pipes,  preventing  the  feed  water  from  freely  entering  the  boiler. 
It  clogs  the  connections  to  the  water  gage,  causing  it  to  indicate 
ample  water  when  it  is  at  a  low  level  in  the  boiler.  Pieces  get  under 
valves  and  prevent  their  closure. 

Scale  in  boilers  is  a  serious  matter,  and  in  order  to  prevent  its 
accumulation,  it  is  good  practice  to  eliminate  the  scale-forming 
matter  from  the  feed  water  before  allowing  it  to  enter  the  boiler. 
This  can  be  accomplished  either  mechanically  by  means  of  separators, 
or  chemically  by  treating  the  water  in  vats  especially  arranged  for 
the  purpose.  If  preferred,  compound  may  be  fed  with  the  water  into 
the  boiler,  but  in  such  case  the  water  should  be  analyzed,  and  the 
proper  compound  prescribed  by  a  chemist  making  a  specialty  of  such 
matters.  Kerosene  fed  into  the  boiler  has  proved  beneficial  in  many 
instances. 

Inspection  and  Insurance. — It  is  an  almost  universal  custom  for 
boiler  owners  to  have  their  boilers  insured  and  inspected.  The  in- 
surance serves  as  a  guarantee  that  the  inspections  will  be  intelligently 
and  carefully  made  and  the  inspections  lessen  the  chance  of  ac- 
cident. 

When  boiler  insurance  is  carried,  an  inspector  visits  the  plant  at 
regular  intervals  and  critically  examines  the  boilers,  both  internally 
and  externally.  During  the  past  10  years  the  company  represented 
by  Mr.  Boehm  made  1,101,140  examinations  and  reported  140,989  de- 
fects, many  of  which  consisted  of  dangerous  fractures  in  or  near  the 
riveted  seams,  and  that  one  boiler  out  of  every  eight  examined,  con- 
tained defects  serious  enough  to  warrant  their  being  reported. 


BOILER   TROUBLES  AND  BOILER  USERS'  COMPLAINTS.    553 

Clinkering  in  Furnaces.* — Clinkering  increases  the  cost  of  the 
heat  liberated  from  the  coal  (1)  by  decreasing  the  efficiency  and 
capacity  of  the  furnace,  (2)  by  increasing  the  labor  cost,  and  (3)  by 
shortening  the  life  of  the  fire-bars  and  of  the  fire-brick  lining.  Oc- 
casionally it  may  interrupt  entirely  the  operation  of  a  plant,  as 
when  a  badly  clinkering  batch  of  coal,  used  on  a  chain  grate,  clogs  up 
the  moving  parts  entirely. 

Clinkering  is  a  result  of  fusion  and  is  some  function  of  the  fusibility 
of  the  ash.  The  fusing  temperature  of  an  ash  is  not  generally  a 
single- valued  temperature.  At  some  particular  temperature,  some  one 
constituent  of  the  ash  will  melt ;  if  it  is  a  minor  constituent  the  effect 
may  be  that  the  ash  becomes  a  viscous  pasty  mass.  At  higher  tem- 
peratures other  constituents  may  melt  and  the  mass  will  become  more 
liquid.  In  other  cases,  the  ash  may  become  liquid  as  soon  as  the 
initial  melting  temperature  is  passed.  If  the  melt  is  very  viscous, 
we  shall  get  a  sticky  mass  which  will  attach  to  itself  the  surrounding 
coal  and  ash  and  form  a  troublesome  clinker ;  if  it  is  more  fluid  it  will 
run  on  the  grate  bars  and  will  in  part  freeze  there  and  may  be  difficult 
to  detach;  if  it  is  extremely  fluid  and  melts  at  a  temperature  very 
much  below  that  of  the  fire,  it  might  possibly  flow  from  the  fire  like 
water  and  give  very  little  trouble. 

The  chemical  compounds  in  ash  are  principally  the  oxides  of 
aluminium  (A1203),  of  silica  (Si02),  of  iron  (FeO  or  Fe203),  of  lime 
(CaO),  of  potash  (K20),  of  magnesium  (MgO),  of  sodium  (Na,0), 
of  sulphur  (S03),  and  to  a  lesser  degree  of  manganese,  phosphorus, 
zinc,  lead  and  other  elements.  Chemical  analysis  will  disclose  the 
weights  of  these  constituents  but  will  in  general  fail  to  show  how  they 
are  combined  with  one  another. 

Alumina  (A1203)  is  the  most  infusible,  melting  at  a  temperature 
higher  than  3450°  F. ;  silica  melts  at  about  2600°  F.  A  mixture  of 
alumina  and  silica  melts  at  some  intermediate  temperature,  the  tem- 
perature falling  as  the  silica  increases.  One  part  of  alumina  with 
five  parts  of  silica  melts  at  3180°  F. ;  one  part  of  alumina  with  ten 
parts  of  silica  at  3075°  F.  A  comparatively  small  amount  of  alumina 
has  a  considerable  influence  in  raising  the  temperature  of  fusion  of 
silica. 

The  temperature  in  a  boiler  furnace  is  probably  never  greater 
than  3200°  F. — usually  it  is  considerably  less.  It  is  obvious  then, 
that  a  mixture  of  alumina  and  silica  will  be  infusible  in  a  boiler 
furnace  so  long  as  a  minimum  of  10  per  cent  of  alumina  is  present. 
But  there  is  very  little  coal  ash  with  as  little  as  10  per  cent  of 
alumina.  The  usual  amount  is  from  20  to  40  per  cent. 

The  iron  and  other  compounds  that  are  present  may  all  be  re- 
garded as  fluxes,  tending  to  reduce  the  melting  point  of  the  alumina- 

*  Condensed  from  a  paper  by  Professor  Lionel  S.  Marks  in  Engineering  News, 
Dec.  8,  1910. 


554  STEAM-BOILER  ECONOMY. 

silica  mixture.  "When  the  constituents  are  mixed  in  such  proportions 
as  to  give  the  lowest  fusing  temperature,,  we  have  what  is  called  the 
"eutectic"  mixture.  A  mixture  of  45  per  cent  of  Si02  with  55  per 
cent  FeO  melts  at  2050°  F.;  with  10  per  cent  CaO  substituted  for 
FeO,  we  get  the  eutectic  melting  at  1940°  F. ;  with  45  per  cent  of  CaO 
substituted  for  FeO,  the  melting  temperature  rises  to  about  2460°  F. 
A  mixture  of  32  per  cent  Si02,  36  per  cent  FeO  and  32  per  cent  CaO 
melts  at  2100°  F.;  with  5  per  cent  of  the  CaO  replaced  by  A1203  we 
get  the  eutectic,  melting  at  2030°  F. 

It  is  probable  that  an  ash  will  not  give  trouble  by  clinkering  under 
usual  furnace  conditions  when  the  fusing  temperature  is  above  2700°  F. 
and  that  the  trouble  experienced  will  increase  as  the  melting  tempera- 
ture falls  below  this  temperature,  for  a  range  of  several  hundred 
degrees.  In  the  present  state  of  knowledge  it  is  impossible  to  tell 
from  a  chemical  analysis  what  will  be  the  fusing  temperature  and  how 
much  trouble  will  arise  from  clinkers.  Further,  the  fusing  tem- 
perature is  not  always  a  definite  temperature  but  may  cover  a  con- 
siderable range  of  temperatures.  The  trouble  from  clinkers  also  de- 
pends on  the  viscosity  of  the  melt,  which  is  not  a  function  of  melting 
temperatures. 

The  influence  of  sulphur  is  undoubtedly  considerable  in  some 
cases,  but  the  clinkering  depends  on  the  percentage  of  sulphur  in 
the  ash,  rather  than  the  percentage  of  sulphur  in  the  coal. 
High  sulphur  is  commonly  accompanied  by  high  ash,  and  the 
sulphur  is  not  then  necessarily  very  troublesome.  As  much  as  5Vo 
per  cent  sulphur  may  exist  in  a  coal  without  causing  clinkering. 
When,  however,  the  percentage  of  sulphur  in  the  ash  is  high,  much 
clinkering  is  likely  to  result.  The  effects  of  sulphur  are  well  set  forth 
as  "follows  in  the  report  of  the  U.  S.  Geological  Survey  (Bulletin  325.)  : 

Sulphur  is  an  undesirable  element  in  coal.  It  generally  occurs  in  combi- 
nation with  iron  as  iron  pyrites,  and  in  combination  with  cajcium,  as  calcium 
sulphate,  or  gypsum.  Pyrites  can  readily  be  recognized  by  its  heavy  weight, 
bright  brass-like  color,  and  crystalline  structure.  The  calcium  sulphate  occurs 
in  small  ,thm,  white  flakes,  more  or  less  transparent.  Of  the  two  sulphur  com- 
pounds, the  pyrites  is  generally  in  larger  quantity  in  coal,  and  is  harmful  because 
it  increases  the  tendency  of  the  coal  to  clinker.  The  clinkering  is  especially 
bad  if  the  percentage  of  ash  is  small  in  proportion  to  the  sulphur.  In  such  coals, 
the  pyrites  and  the  ash  fuse  together  and  form  a  thin  layer  of  solid  clinker, 
which  effectively  stops  the  passage  of  air  through  the  grate,  thereby  permitting 
the  grate  bars  to  become  heated  from  the  hot  fuel  bed  just  above.  The  clinker 
then  melts  down  into  the  spaces  between  the  bars  and  the  sulphur  seems  to 
combine  with  the  iron  of  the  grate.  The  heat  warps  the  grate  bars,  and  the 
clinker  has  such  corrosive  action  on  the  hot  iron  that  a  set  of  grate  bars  is 
destroyed  in  the  course  of  a  few  days.  When  such  clinkering  occurs  any  attempt 
to  slice  the  fire  fails,  and  only  slow  and  very  difficult  cleaning  of  the  fires  will 
remove  the  clinkers. 

A  common  view  as  to  clinkering  is  that  it  is  caused  by  iron.  The 
presence  of  iron  certainly  results  in  a  lowering  of  the  melting  tem- 
perature— and  so  far  as  the  presence  of  iron  means  the  presence  of 


BOILER  TROUBLES  AND  BOILER   USERS'  COMPLAINTS.      555 

sulphur,  there  may  be  that  secondary  reason  for  clinkering.  The  tests 
of  the  U.  S.  Geological  Survey  show  a  decided  increase  in  the  per- 
centage of  clinker  in  the  refuse,  as  the  percentage  of  iron  in  the  coal 
increases. 

It  is  probable  that  the  fire-bars  waste  away,  wherever  contact  takes 
place  with  molten  iron  or  with  ordinary  molten  clinker,  in  two  ways : 
(1)  by  direct  melting  and,  (2)  by  chemical  combination  or  solution. 
The  latter  is  undoubtedly  the  more  active  agent,  since  it  will  in  gen- 
eral result  in  a  lowering  of  the  melting  temperature  of  the  cast  iron 
and  may  be  accompanied  by  evolution  of  heat. 

The  size  of  coal  has  apparently  no  effect  on  clinkering.  No 
variations  can  be  detected  in  the  formation  of  clinker  when  the  size 
"of  the  coal  is  changed. 

The  possible  methods  for  preventing  clinkers  are : 

(1)  Eeducing   the   temperature   of   combustion   in   the   furnace. 
This  can  be  accomplished  by  sending  more  air  through  the  fire,  but  it 
will  always  be  accompanied  by  a  reduction  in  efficiency. 

(2)  For  coals  high  in  ash,  the  use  of  steam  blown  in  from  below 
the  grate  will  prevent  the  clinkers  freezing  on  the  grate,  and  will  per- 
mit longer  periods  of  operation  between  cleanings  of  the  fire.     With 
some  clinkers  this  method  is  not  found  to  give  much  relief. 

(3)  The  fusing  temperature  or  viscosity  of  the  ash  might  be  raised 
by  mixing  certain  substances  with  the  coal  so  as  to  prevent  either  the 
fusing  of  the  ash  or  the  flow  after  fusing. 

(4)  The  fusing  temperature  and  viscosity  might  be  so  much  re- 
duced by  the  admixture  of  various  fluxes,  that  the  fused  material  would 
run  through  the  grates  like  water  without  freezing  on  them. 

A  series  of  experiments  on  methods  (3)  and  (4)  was  carried  on 
by  Prof.  Marks,  but  the  results  were  practically  unimportant. 

The  results  of  the  inquiry  are  summed  up  as  follows:  The  ele- 
ments the  presence  of  which  cause  trouble  from  clinkering  are  prin- 
cipally calcium,  iron  and  sulphur.  The  exact  amounts  of  these  which 
may  be  present  without  causing  trouble  is  not  at  present  known  with 
sufficient  accuracy  to  permit  the  use  of  a  formula  (such  as  Frost's) 
with  any  security.  The  only  real  cure  for  clinkering  is  low-tem- 
perature combustion.  If  the  temperatures  are  high  the  trouble  from 
clinkering  can  generally  be  reduced  by  the  use  of  steam,  or  by  the 
addition  of  kaolin  or  pure  quartz,  both  of  which,  however,  are  too 
expensive  to  be  commercially  justifiable. 

The  author  has  had  considerable  experience  with  clinkering  coals, 
and  would  add  to  the  remedies  suggested  by  Prof.  Marks  the  follow- 
ing: 

1.  Large  grate  surface,  reducing  the  rate  of  combustion  and  the 
amount  of  clinker  formed  per  square  foot,  of  grate. 

2.  Low  temperature  combustion  on  the  grate  produced  not  by  an 


556  STEAM-BOILER  ECONOMY. 

excess  but  by  a  deficiency  of  air,  the  combustion  being  completed  with 
an  additional  air  supply  in  a  fire-brick  combustion  chamber  removed 
from  the  grate. 

3.  Shaking  and  dumping  grates,  to  remove  the  clinker  before  it  is 

formed  in  large  masses. 


CHAPTER  XVI. 
EVAPORATION   TESTS   OF  STEAM-BOILERS. 

Object  of  an  Evaporation  Test. — The  principal  object  of  an 
evaporation  test  of  a  steam-boiler  is  to  find  out  how  many  pounds 
of  water  it  evaporates  under  a  certain  set  of  conditions  in  a  given 
time,  and  how  many  pounds  of  ooal  are  required  to  effect  this  evapo- 
ration. The  test  may  be  made  for  one  or  more  of  several  purposes, 
viz: 

1.  To  determine  whether  or  not  the  stipulations  of  a  contract 
between  the  seller  and  the  buyer  of  a  boiler  (or  of  an  appendage 
to  the  boiler,  such  as  a  furnace)  have  been  performed. 

2.  To  determine  the  relative  economy  of  different  kinds  of  fuel,* 
of  different  kinds  of  furnace,  or  of  different  methods  of  driving. 

3.  To  determine  whether  or  not  the  boilers,  as  ordinarily  run 
under  the  every-day  conditions  of  the  plant,  are  operated  as  econ- 
omically as  they  should  be. 

4.  To  determine,  in  case  the  boilers  either  fail  to  furnish  easily 
the  quantity  of  steam  desired,  or  else  furnish  it  at  what  is  supposed 
to  be  an  excessive  cost  for  fuel,  whether  any  additional  boilers  are 
needed  or  whether  some  change  in  the  conditions  of  running  is  a 
sufficient  remedy  for  the  difficulty. 

For  the  first  of  the  above-named  purposes,  it  is  necessary  that 
the  test  should  be  made  with  every  precaution  to  insure  accuracy, 
such  as  those  described  in  the  Code  of  the  Committee  of  the  Ameri- 
can Society  of  Mechanical  Engineers,*  (see  abstract  below). 
Experts  in  boiler-testing  should  be  employed,  and  the  water  fed 
to  the  boiler  should  be  weighed,  or  measured  in  calibrated  tanks, 

*  Trans.  A.S.M.E.,  1915,  Reprinted  in  pamphlet  form  by  the  Society.  The 
first  committee  of  the  society  on  boiler-tests  reported  in  1885,  the  second  in 
1899.  In  1909  a  committee  on  Tests  of  Power  Plant  Apparatus  was  appointed; 
its  preliminary  report  was  published  in  1912,  arid  its  final  report  in  1915.  The 
author  was  chairman  of  the  first  committee  and  member  of  the  other  two. 

557 


558  STEAM-BOILER  ECONOMY. 

and  not  by  a  water-meter,  which  is  apt  not  only  to  have  an  error 
at  its  average  rate  of  running,  but  also  an  error  which  varies  with 
every  change  in  the  rate.  For  the  other  three  purposes,  however, 
water-meters,  if  calibrated  before  and  after  the  test  by  means  of 
running  water  through  them,  at  the  average  rate  and  pressure  used 
in  the  test,  into  a  tank  set  on  a  platform  scale,  are  sufficiently 
accurate,  and  the  regular  engineering  force  of  the  establishment 
should  be  capable  of  making  the  test. 

In  large  plants,  in  which  the  yearly  cost  of  coal  amounts  to  some 
thousands  of  dollars,  there  are  apt  to  be  wastes  of  fuel,  amounting 
to  as  much  as  10  or  20  per  cent  of  the  total  consumption,  which 
are  unsuspected  until  they  are  discovered  by  a  series  of  tests. 
When  several  boilers  discharge  their  gases  into  the  same  flue  leading 
to  the  chimney,  unless  the  draft  conditions  at  each  boiler  are  care- 
fully equalized,  one  or  more  of  the  boilers  is  likely  to  be  running 
under  unfavorable  draft  conditions.  If  the  boilers  are  of  different 
types  or  different  proportions  of  grate  and  heating  surface,  the  draft 
and  the  method  of  firing  which  are  best  for  one  boiler  may  not  be 
best  for  another.  For  these  reasons  it  is  important  in  designing 
and  constructing  a  large  boiler  plant  to  arrange  the  feed-pipes  so 
that  a  meter  may  at  any  time  be  placed  in  the  feed-pipe  of  any 
one  of  the  boilers,  in  order  that  a  test  of  24  hours,  or  a  week,  if 
desired,  may  easily  be  made.  It  is  an  easy  matter  to  weigh  all  the 
coal  used  by  the  boiler  during  the  test,  and  to  keep  hourly  records 
of  the  coal-  and  water-consumption,  the  steam  pressure,  and  the 
temperatures  of  the  feed-water  and  the  waste  gases. 

Besides  the  tests  of  each  boiler  in  a  plant,  which  ought  to  be 
made  occasionally,  say  every  two  or  three  years,  a  continuous 
record  of  the  performance  of  the  plant  may  be  made  by  having  a 
large  meter  in  the  main  feed-line,  noting  the  water-consumption 
daily,  weekly  or  monthly,  and  comparing  it  with  the  monthly 
coal  bills.  In  electric  light  and  power  stations  the  boiler-record 
should  be  compared  with  the  record  of  the  electric  current  given 
by  the  volt  and  ampere  meters. 

For  all  important  tests,  where  the  greatest  accuracy  is  essential, 
the  provisions  of  the  Code,  the  principal  parts  of  which  relating 
to  steam  boilers  are  given  in  condensed  form  below,  should  be 
followed. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  559 

INSTRUCTIONS  REGARDING  TESTS  IN  GENERAL. 
(Code  of  1915). 

OBJECT. 

Ascertain  the  specific  object  of  the  test,  and  keep  this  in  view 
not  only  in  the  work  of  preparation,  but  also  during  the  progress 
of  the  test. 

If  questions  of  fulfillment  of  contract  are  involved,  there  should 
be  a  clear  understanding  between  all  the  parties,  preferably  in 
writing,  as  to  the  operating  conditions  which  should  obtain  during 
the  trial,  the  methods  of  testing  to  be  followed,  corrections  to  be 
made  in  case  the  conditions  actually  existing  during  the  test  differ 
from  those  specified,  and  all  other  matters  about  which  dispute 
may  arise,  unless  these  are  already  expressed  in  the  contract  itself. 

PREPARATIONS. 

Dimensions.  Measure  the  dimensions  of  the  principal  parts 
of  the  apparatus  to  be  tested,  so  far  as  they  bear  on  the  objects  in 
view,  or  determine  them  from  working  drawings.  Notice  the  gen- 
eral features  of  the  apparatus,  both  exterior  and  interior,  and  make 
sketches,  if  needed,  to  show  unusual  points  of  design. 

The  areas  of  the  heating  surfaces  of  boilers  and  superheaters  to  be  found  are 
those  of  surfaces  in  contact  with  the  fire  or  hot  gases.  The  submerged 
surfaces  in  boilers  at  the  mean  water  level  should  be  considered  as  water- 
heating  surfaces,  and  other  surfaces  which  are  exposed  to  the  gases  as 
superheating  surfaces. 

Examination  of  Plant.  Make  a  thorough  examination  of  the 
physical  condition  of  all  parts  of  the  plant  or  apparatus  which 
concern  the  object  in  view,  and  record  the  conditions  found. 

In  boilers  examine  for  leakage  of  tubes  and  riveted  or  other  metal  joints.  Note 
the  condition  of  brick  furnaces,  grates  and  baffles.  Examine  brick  walls  and 
cleaning  doors  for  air  leaks,  either  by  shutting  the  damper  and  observing 
the  escaping  smoke  or  by  candlerflame  test.  Determine  the  condition 
of  heating  surfaces  with  reference  to  exterior  deposits  of  soot  and  interior 
deposits  of  mud  or  scale. 

If  the  object  of  the  test  is  to  determine  the  highest  efficiency 
or  capacity  obtainable,  any  physical  defects,  or  defects  of  opera- 
tion, tending  to  make  the  result  unfavorable  should  first  be  remedied; 
all  fouled  parts  being  cleaned,  and  the  whole  put  in  first-class 
condition.  If,  on  the  other  hand,  the  object  is  to  ascertain  the 
performance  under  existing  conditions,  no  such  preparation  is  either 
required  or  desired. 

Precautions  against  Leakage.  In  steam  tests  make  sure  that 
there  is  no  leakage  through  blowoffs,  drips,  etc.,  or  any  steam  or 
water  connections,  which  would  in  a*ky  way  affect  the  results. 


560  STEAM-BOILER  ECONOMY. 

All  such  connections  should  be  blanked  off,  or  satisfactory  assurance 
should  be  obtained  that  there  is  leakage  neither  out  nor  in. 

Apparatus  and  Instruments.  See  that  the  apparatus  and  instru- 
ments are  substantially  reliable,  and  arrange  them  in  such  a  way 
as  to  obtain  correct  data. 

Weighing  Scales.  For  determining  the  weight  of  coal,  oil,  water,  etc.,  ordinary 
platform  scales  serve  every  purpose.  Too  much  dependence,  however,  should 
not  be  placed  upon  their  reliability  without  first  calibrating  them  by  the 
use  of  standard  weights,  and  carefully  examining  the  knife-edges,  bearing 
plates,  and  ring  suspensions,  to  see  that  they  are  all  in  good  order. 

For  testing  locomotives  and  some  classes  of  marine  boilers,  where  room 
is  lacking,  sacks  or  bags  are  sometimes  required  to  facilitate  the  handling 
of  coal,  the  weighing  being  done  before  loading  on  the  tender  or  delivery  to 
the  fire  room. 

Water  Weighing  and  Measuring  Apparatus.  Wherever  practicable  the  feed- 
water  should  be  weighed,  especially  for  guarantee  tests.  The  most  satis- 
factory and  reliable  apparatus  for  this  purpose  consists  of  one  or  more 
tanks  each  placed  on  platform  scales,  these  being  elevated  a  sufficient 
distance  above  the  floor  to  empty  into  a  receiving  tank  placed  below,  the 
latter  being  connected  to  the  feed  pump.  Measuring  tanks  calibrated 
by  weighing  may  also  be  used. 

In  tests  of  complete  steam  power  plants,  where  it  is  required  to  measure 
the  feedwater  without  unnecessary  change  in  the  working  conditions,  a 
water  meter  may  be  employed.  Meter  measurement  may  also  be  required 
in  many  other  cases,  such  as  locomotive  and  marine  service.  The  accu- 
racy of  meters  should  be  determined  by  calibration  in  place  under  the 
conditions  of  use. 

If  a  large  quantity  of  water  is  to  be  measured,  an  automatic  water-weigher, 
a  rotary,  disk,  or  Venturi  meter,  a  weir,  or  some  form  of  orifice  measure- 
ment may  be  employed.  The  measuring  apparatus  should  be  calibrated 
under  the  conditions  of  use,  unless  its  design  is  such  that  standard  formulae 
and  constants  may  be  applied  for  determining  the  discharge.  If  recording 
mechanism  is  employed  in  connection  with  orifice  or  weir  measuring  appa- 
ratus, make  sure  that  its  record  is  reliable. 

Steam  Measuring  Apparatus.  Various  forms  of  steam  meters  may  be  employed 
for  measuring  steam,  provided  such  meters  are  properly  calibrated  under 
conditions  of  use,  and  the  pulsations  of  pressure,  if  any,  are  not  serious. 

Pressure  Gages.  For  determining  pressure  the  gages  belonging  to  the  plant 
may  be  used,  provided  they  are  compared  with  a  standardized  gage  of 
the  spring  or  mercury  type  and  verified,  due  allowance  being  made  for  the 
head  of  water,  if  any,  standing  in  the  connecting  pipe.  Such  comparisons 
should  be  made  with  both  gages  at  their  respective  normal  temperatures. 
In  the  use  of  spring  gages  for  steam  the  gages  should  be  protected  by 
proper  syphons  or  water  seals  and  no  leakage  should  be  allowed  at  the 
gage-cock.  The  gages  should  also  be  located  so  that  they  will  not  be 
unduly  heated. 

Thermometers.  Thermometers  should  be  of  the  kind  having  graduations  marked 
on  the  glass  stem.  Those  used  for  temperatures  above  the  boiling  point 
of  mercury  (or  say  above  500°  F.)  should  have  nitrogen  in  the  top  of  the 
bore.  They  should  also  have  a  small  safety  bulb  at  the  top.  Thermom- 
eters constructed  in  this  way  can  be  used  satisfactorily  up  to  1000°  F. 

Thermometers  which  are  used  for  important  data  should  be  calibrated 
before  and  after  a  test,  by  reference  to  standard  thermometers. 

Pyrometers.  Metallic  pyrometers  used  for  determining  high  temperatures 
must  be  handled  cautiously  owing  to  the  difficulty  of  exposing  the  whole 
of  the  stem  to  the  current  of  gas,  the  temperature  of  which  is  to  be  deter- 
mined. Electric  pyrometers  either  of  the  thermo-couple  or  resistance 
type  are  satisfactory  for  this  work  within  their  practical  range,  which  is 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  561 

1800°  F.  for  iron-nickel  couples  and  3000°  F.  for  platinum-iridium  couples 
or  platinum  resistance  pyrometers.  Instruments  of  this  kind  can  readily 
be  calibrated  by  comparing  them  at  low  ranges  of  temperature  with  a 
standardized  mercurial  thermometer,  both  being  placed  for  example  in  a 
current  of  hot  air  the  temperature  of  which  is  under  control.  For  extremely 
high  temperatures  such  as  that  of  a  boiler  furnace,  the  optical,  pneumatic, 
and  radiation  pyrometers  may  be  used.  The  calibration  of  high-tem- 
perature instruments  can  best  be  undertaken  in  a  laboratory  especially 
fitted  for  the  purpose. 

Draft  Gages.  When  the  ordinary  U-tube  is  kept  clean  and  the  two  legs  are  close 
together  with  the  scale  extending  at  least  to  the  center  of  each  leg,  it  gives 
satisfactory  indications.  For  measuring  small  amounts  of  draft  some 
form  of  multiplying  gage  may  be  employed,  such  as  a  U-tube  in  which  one 
leg  is  inclined  from  the  horizontal,  the  multiplication  varying  inversely  as 
the  sine  of  the  angle  of  inclination,  the  tube  being  filled  with  a  light  mineral 
oil.  These  can  be  calibrated  by  comparison  with  the  simple  U-tube  gage 
when  indicating  a  high-draft,  say  one  inch  or  more.  It  is  preferable  to  use 
kerosene  instead  of  water  in  the  U-tube,  and  make  allowance  for  the  dif- 
ference of  specific  gravity.  Draft  readings  should  be  expressed  in  inches  of 
water-column. 

Steam  Calorimeters.  The  most  satisfactory  instruments  for  determining  the 
amount  of  moisture  in  steam  are  calorimeters  that  operate  upon  the 
throttling  principle,  or  that  combine  the  throttling  and  separating  prin- 
ciples; the  orifice  used  being  of  such  size  as  to  throttle  to  atmospheric 
pressure,  and  the  instrument  being  provided  with  two  thermometers,  one 
showing  the  temperature  above  the  orifice  and  the  other  that  below  it.  In- 
struments working  on  the  separating  principle  alone  may  also  be  employed; 
also  certain  forms  of  electric  calorimeters. 

Fuel  Calorimeters.  To  determine  the  total  heat  of  combustion  of  a  sample 
of  coal  or  other  fuel,  the  best  form  of  calorimeter  is  one  in  which  the  fuel 
is  burned  in  an  atmosphere  of  oxygen  gas.  The  Mahler  type  of  calorim- 
eter is  recognized  as  the  most  complete  and  accurate  apparatus  of  this 
kind.  The  total  heat  of  combustion  of  gas  should  be  found  by  burning 
the  gas  in  the  Junker  calorimeter. 

Smoke  Determination.  No  wholly  satisfactory  methods  for  smoke  determina- 
tions have  yet  come  into  use,  nor  have  any  reliable  methods  been  established 
for  definitely  fixing  even  the  relative  density  of  the  smoke  issuing  from 
chimneys  at'  different  times.  One  method  commonly  employed  which 
answers  the  purpose  fairly  well,  is  that  of  making  frequent  visual  observa- 
tions of  the  chimney  at  intervals  of  one  minute  or  less  for  a  period  of  one 
hour  and  recording  the  observed  characteristics  according  to  the  degree 
of  blackness  and  density,  and  giving  to  the  various  degrees  of  smoke  an 
arbitrary  percentage  value  rated  in  some  such  manner  as  that  expressed 
in  the  following  table: 

SMOKE    PERCENTAGES 

Dense  black 100 

Medium  black 80 

Dense  gray 60 

Medium  gray 40 

Light  gray 20 

Very  light 5 

Trace 1 

Clear  chimney .....: 0 

The  color  and  density  of  smoke  depend  somewhat  on  the  character  of 
the  sky  or  other  background,  and  on  the  air  and  weather  conditions 
obtaining  when  the  observation  is  made,  and  these  should  be  given  due 
consideration  in  making  comparisons.  Observations  of  this  kind  are  also 


562  STEAM-BOILER  ECONOMY. 

subject  to  personal  errors  and  errors  of  judgment.  Nevertheless,  these 
methods  are  useful,  especially  when  the  results  are  plotted,  according  to 
the  percentage  scale  determined  on,  so  that  a  graphic  representation  of  the 
changes  can  be  shown. 


SAMPLING    AND    DRYING    COAL 

Select  a  representative  shovelful  from  each  barrow-load  as  it 
is  drawn  from  the  coal  pile  or  other  source  of  supply,  and  store  the 
samples  in  a  cool  place  in  a  covered  metal  receptacle.  When  all 
the  coal  has  thus  been  sampled,  break  up  the  lumps,  thoroughly 
mx  the  whole  quantity,  and  finally  reduce  it  by  the  process  of 
reipeated  quartering  and  crushing  to  a  sample  weighing  about 
5  lb.,  the  largest  pieces  being  about  the  size  of  a  pea.  From  this 
sample  two  1-qt.  air-tight  glass  fruit  jars,  or  other  air-tight  vessels, 
are  to  be  promptly  filled  and  preserved  for  subsequent  determina- 
tions of  moisture,  calorific  value,  and  chemical  composition. 

When  the  sample  lot  of  coal  has  been  reduced  by  quartering  to 
say  100  lb.,  a  portion  weighing  say  15  to  20  lb.  should  be  with- 
drawn for  the  purpose  of  immediate  moisture  determination.  This 
is  placed  in  a  shallow  iron  pan  and  dried  on  the  hot  iron  boiler 
flue  for  at  least  12  hours,  being  weighed  before  and  after  drying 
on  scales  reading  to  quarter  ounces. 

The  moisture  thus  determined  is  approximately  reliable  for 
anthracite  and  semi-bituminous  coals,  but  not  for  coals  containing 
much  inherent  moisture.  For  such  coals,  and  for  all  reliable 
determinations  the  method  to  be  pursued  is  as  follows: 

Take  one  of  the  samples  contained  in  the  glass  jars,  and  subject  it  to  a  thorough 
air  drying,  by  spreading  it  in  a  thin  layer  and  exposing  it  for  several 
hours  to  the  atmosphere  of  a  warm  room,  weighing  it  before  and  after, 
thereby  determining  the  quantity  of  surface  moisture  it  contains.  Then 
crush  the  whole  of  it  by  running  it  through  an  ordinary  coffee  mill  or 
other  suitable  crusher  adjusted  so  as  to  produce  somewhat  coarse  grains 
(less  than  ^  in.),  thoroughly  mix  the  crushed  sample,  select  from  it  a  por- 
tion of  from  10  to  50  grams  (say  £  oz.  to  2  oz),  weigh  it  in  a  balance  which  will 
easily  show  a  variation  as  small  as  1  part  in  1000,  and  dry  it  for  one  hour 
in  an  air  or  sand  bath  at  a  temperature  between  240  and  280°  F.  Weigh 
it  and  record  the  loss,  then  heat  and  weigh  again  until  the  minimum  weight 
has  been  reached.  The  difference  between  the  original  and  the  minimum 
weight  is  the  moisture  in  the  air-dried  coal.  The  sum  of  the  moisture  thus 
found  and  that  of  the  surface  moisture  is  the  total  moisture. 

If  a  large  drying  oven  is  available  the  moisture  may  be  determined  by 
heating  one  of  the  glass  jars  full  of  coal,  the  cover  being  removed,  at  a  tem- 
perature between  240°  and  280°  F.  until  it  reaches  the  minimum  weight. 

With  certain  lignites  lower  temperatures  for  drying  may  be  advisable. 

SAMPLING    ASHES   AND    REFUSE. 

The  general  method  above  described  may  also  be  followed  for 
obtaining  a  sample  of  the  ashes  and  refuse,  and  for  determining 
the  amount  of  moisture,  if  any,  in  the  sample. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  563 

SAMPLING    STEAM. 

Construct  a  sampling  pipe  or  nozzle  made  of  ^-in.  iron  pipe  and 
insert  it  in  the  steam  main  at  a  point  where  the  entrained  moisture 
is  likely  to  be  most  thoroughly  mixed.  The  inner  end  of  the  pipe, 
which  should  extend  nearly  across  to  the  opposite  side  of  the  main, 
should  be  closed  and  the  interior  portion  perforated  with  not  less 
than  twenty  J-in.  holes  equally  distributed  from  end  to  end  and 


#in.  holes  drilled 
helically  along  pipe 


FIG.  244. — PIPE  FOR  SAMPLING  STEAM, 

preferably  drilled  in  irregular  or  spiral  rows,  with  the  first  hole  not 
less  than  half  an  inch  from  the  wall  of  the  pipe.     (See  Fig.  244.) 

The  sampling  pipe  should  not  be  placed  near  a  point  where  water  may  pocket 
or  where  such  water  may  effect  the  amount  of  moisture  contained  in  the 
sample. 

PROXIMATE    ANALYSIS    OF    AIR-DRIED    COAL. 

To  determine  volatile  matter  place  about  one  gram  of  the  air- 
dried  powdered  coal  in  the  crucible  and  heat  it  in  a  drying  oven 
to  220°  F.  for  one  hour  (or  longer  if  necessary  to  obtain  the  minimum 
weight),  cool  in  a  dessicator  and  weigh.  Cover  the  crucible  with 
a  loose  platinum  plate.  Heat  7  minutes  with  a  Bunsen  burner 
giving  a  6  to  8-in.  flame,  the  crucible  being  supported  3  in.  above 
the  top  of  the  burner  tube  and  protected  from  outside  air  currents 
by  a  cylindrical  asbestos  chimney  3  in.  diameter.  Cool  in  a  des- 
sicator, remove  the  cover  and  weigh.  The  loss  in  weight  repre- 
sents the  volatile  matter. 

To  ascertain  the  ash,  heat  the  residue  in  thp  crucible  by  a  blast 
lamp  until  it  is  completely  burned,  using  a  stream  of  oxygen  if 
desired  to  hasten  the  process.  The  residue  is  the  ash. 

The  difference  between  the  residue  left  after  the  expulsion  of 
the  volatile  matter  and  the  ash  is  the  fixed  carbon. 


SAMPLING    FLUE    GASES. 

The  sample  for  flue  gas  analysis  should  be  drawn  from  the  region 
near  the  center  of  the  main  body  of  escaping  gases,  using  a  sampling 
pipe  not  larger  than  £-in.  gas  pipe.  The  point  selected  should 
be  one  where  there  is  no  chance  for  air-leakage  into  the  flue  which 


564  '    STEAM-BOILER  ECONOMY. 

could  affect  the  average  quality.  In  a  round  or  square  flue  having 
an  area  of  nor  more  than  one-eighth  of  the  grate  surface,  the 
sampling  pipe  may  be  introduced  horizontally  at  a  central  line, 
or  preferably  a  little  higher  than  this  line,  and  the  pipe  should 
contain  perforations  extending  the  whole  length  of  the  part  im- 
mersed, pointing  toward  the  current  of  gas,  the  collective  area  of 
the  perforations  being  less  than  the  area  of  the  pipe.  The  pipe 
should  be  frequently  removed  and  cleaned. 

It  is  advisable  to  take  samples  both  from  the  flue  and  from  the 
furnace,  so  as  to  determine  the  amount  of  air  leakage  through  the 
setting  and  the  changes  in  the  composition  of  the  gas  between  the 
furnace  and  the  flue, 

It  is  best  to  draw  a  continuous  sample,  using  a  suitable  aspirator,  and 
provide  a  branch  pipe  from  which  to  obtain  the  test-sample.  The  test 
sample  can  then  be  taken  either  momentarily  or  continuously,  according 
to  the  requirements. 

MISCELLANEOUS    INSTRUCTIONS. 

The  person  in  charge  of  a  test  should  have  the  aid  of  a  sufficient 
number  of  assistants,  so  that  he  may  be  free  to  give  special  atten- 
tion to  any  part  of  the  work  whenever  and  wherever  it  may  be 
required.  He  should  make  sure  that  the  instruments  and  testing 
apparatus  continually  give  reliable  indications,  and  that  the  read- 
ings are  correctly  recorded.  He  should  also  keep  in  view,  at  all 
points,  the  operation  of  the  plant  or  part  of  the  plant  under  test 
and  see  that  the  operating  conditions  determined  on  are  main- 
tained and  that  nothing  occurs,  either  by  accident  or  design,  to 
vitiate  the  data.  This  last  precaution  is  especially  needed  in  guar- 
antee tests. 

Before  a  test  is  undertaken,  it  is  important  that  the  boiler, 
engine,  or  other  apparatus  concerned  shall  have  been  in  operation 
a  sufficient  length  of  time  to  attain  working  temperatures  and 
proper  operating  conditions  throughout,  so  that  the  results  of  the 
test  may  express  the  true  working  performance. 

It  would,  for  example,  be  manifestly  improper  to  start  a  test  for  determining 
the  maximum  efficiency  of  an  externally  fired  boiler  with  brick  setting, 
until  the  boiler  had  been  at  work  a  sufficient  number  of  days  to  dry  out 
thoroughly  and  heat  the  brick  work  to  its  working  temperature. 

An  exception  should  be  noted  where  the  object  of  the  test  is 
to  obtain  the  working  performance,  including  the  effect  of  prelim- 
inary heating,  in  which  case  all  the  conditions  should  conform  to 
those  of  regular  service. 

In  preparation  for  a  test  to  demonstrate  maximum  efficiency, 
it  is  desirable  to  run  preliminary  tests  for  the  purpose  of  determin- 
ing the  most  advantageous  conditions. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  565 

OPERATING    CONDITIONS. 

In  all  tests  in  which  the  object  is  to  determine  the  performance 
under  conditions  of  maximum  efficiency,  or  where  it  is  desired  to 
ascertain  the  effect  of  predetermined  conditions  of  operation,  all 
such  conditions  which  have  an  appreciable  effect  upon  the  efficiency 
should  be  maintained  as  nearly  uniform  during  the  trial  as  the 
limitations  of  practical  work  will  permit.  Where  maximum 
efficiency  is  the  object  in  view,  there  should  be  uniformity  in  such 
matters  as  steam  pressure,  times  of  firing,  quantity  of  coal  supplied 
at  each  firing,  thickness  of  fire,  and  in  other  firing  operations;  also 
in  the  rate  of  supplying  the  feedwater,  in  the  load,  and  in  the  opera- 
ting conditions  throughout.  On  the  other  hand,  if  the  object  of 
the  test  is  to  determine  the  performance  under  working  conditions, 
no  attempt  at  uniformity  is  either  desired  or  required  unless  this 
uniformity  corresponds  to  the  regular  practice,  and  when  this  is 
the  object  the  usual  working  conditions  should  prevail  throughout 
the  trial. 

RECORDS. 

A  log  of  the  data  should  be  entered  in  notebooks  or  on  blank 
sheets  suitably  prepared  in  advance.  This  should  be  done  in  such 
manner  that  the  test  may  be  divided  into  hourly  periods,  or  if  neces- 
sary, periods  of  less  duration,  and  the  leading  data  obtained  for  any 
one  or  more  periods  as  desired,  thereby  showing  the  degree  of 
uniformity  obtained. 

The  readings  of  instruments  and  apparatus  concerned  in  the 
test  other  than  those  showing  quantities  of  consumption  (such  as 
fuel,  water,  and  gas),  should  be  taken  at  intervals  not  exceeding 
half  an  hour  and  entered  in  the  log.  When  the  indications  fluctuate, 
the  intervals  should  be  reduced.  In  the  case  of  smoke  observa- 
tions it  is  often  necessary  to  take  observations  every  minute,  or 
still  of  toiler. 

Make  a  memorandum  of  every  event  connected  with  the  prog- 
ress of  a  test,  however  unnecessary  at  the  time  it  may  appear. 
A  record  should  be  made  of  the  exact  time  of  every  such  occurrence 
and  the  time  of  taking  every  weight  and  every  observation.  For 
the  purp>ose  of  identification  the  signature  of  the  observer  and  the 
date  should  be  affixed  to  each  log  sheet  or  record. 

In  the  simple  matter  of  weighing  coal  by  the  barrow-load,  or 
weighing  water  by  the  tank-full,  which  is  required  in  many  tests, 
a  series  of  marks,  or  tallies,  should  never  be  trusted.  The  time 
each  load  is  weighed  or  emptied  should  be  recorded.  The  weighing 
of  coal  should  not  be  delegated  to  unreliable  assistants,  and  when- 
"ver  practicable,  one  or  more  men  should  be  assigned  solely  to  this 
work.  The  same  may  be  said  with  regard  to  the  weighing  of  feed- 
water. 


566  STEAM-BOILER  ECONOMY. 

PLOTTING  DATA  AND  RESULTS. 

If  it  is  desired  to  show  the  uniformity  of  the  data  at  a  glance 
the  whole  log  of  the  trial  should  be  plotted  on  a  chart,  preferably 
while  the  test  is  in  progress,  using  horizontal  distances  to  represent 
times  of  observation,  and  vertical  distances  on  suitable  scales  to 
represent  various  data  as  recorded. 

REPORT. 

The  report  of  a  test  should  present  all  the  leading  facts  bearing 
on  the  design,  dimensions,  condition,  and  operation  of  the  apparatus 
tested,  and  should  include  a  description  of  any  other  apparatus 
and  auxiliaries  concerned,  together  with  such  sketches  as  may  be 
needed  for  a  clear  understanding  of  all  points  under  consideration. 
It  should  state  clearly  the  object  and  character  of  the  test,  the 
methods  followed,  the  conditions  maintained,  and  the  conclusions 
reached,  closing  with  a  tabular  summary  of  the  principal  data 
and  results. 


RULES  FOR  CONDUCTING  EVAPORATIVE  TESTS  OF  BOILERS 
OBJECT  AND  PREPARATIONS. 

Determine  the  object  of  the  test,  take  the  dimensions,  note 
the  physical  conditions,  examine  for  leakages,  install  the  testing 
appliances,  etc.,  as  pointed  out  in  the  general  instructions  and  make 
preparations  for  the  test  accordingly. 

FUEL. 

Determine  the  character  of  fuel  to  be  used.  For  tests  of  maxi- 
mum efficiency  or  capacity  of  the  boiler  to  compare  with  other 
boilers,  the  coal  should  be  of  some  kind  which  is  commercially 
regarded  as  a  standard  for  the  locality  where  the  test  is  made. 

A  coal  selected  for  maximum  efficiency  and  capacity  tests  should 
be  the  best  of  its  class,  and  especially  free  from  slagging  and  un- 
usual clinker-forming  impurities. 

-For  guarantee  and  other  tests  with  a  specified  coal  containing 
not  more  than  a  certain  amount  of  ash  and  moisture,  the  coal 
selected  should  not  be  higher  in  ash  and  in  moisture  than  the 
stated  amounts  because  any  increase  is  liable  to  reduce  the  efficiency 
and  capacity  more  than  the  equivalent  proportion  of  such  increase, 

OPERATING    CONDITIONS. 

Determine  what  the  operating  conditions  and  method  of  firing 
should  be  to  conform  to  the  object  in  view,  and  see  that  they  pre 
vail  throughout  the  trial,  as  nearly  as  possible. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  567 

Where  uniformity  in  the  rate  of  evaporation  is  required,  arrangement  can 
usually  be  made  to  dispose  of  the  steam  so  that  this  result  can  be  attained. 
In  a  single  boiler  it  may  be  accomplished  by  discharging  steam  through  a 
waste  pipe  and  regulating  the  amount  by  means  of  a  valve.  In  a  battery 
of  boilers,  in  which  only  one  is  tested,  the  draft  may  be  regulated  on  the 
remaining  boilers  to  meet  the  varying  demands  for  steam,  leaving  the  test 
boiler  to  work  under  a  steady  rate  of  evaporation. 

DURATION. 

• 

The  duration  of  tests  to  determine  the  efficiency  of  a  hand- 
fired  boiler,  should  be  at  least  10  hours  of  continuous  running,  or 
such  time  as  may  be  required  to  burn  a  total  of  250  Ib.  of  coal  per 
square  foot  of  grate. 

In  the  case  of  a  boiler  using  a  mechanical  stoker,  the  duration, 
where  practicable,  should  be  at  least  24  hours.  If  the  stoker  is  of 
a  type  that  permits  the  quantity  and  condition  of  the  fuel  bed  at 
beginning  and  end  of  the  test  to  be  accurately  estimated,  the  dura- 
tion may  be  reduced  to  10  hours,  or  such  time  as  may  be  required 
to  burn  the  total  of  250  Ib.  per.  sq.  ft. 

In  commercial  tests  where  the  service  requires  continuous  operation  night 
and  day,  with  frequent  shifts  of  firemen,  the  duration  of  the  test,  whether 
the  boilers  are  hand-fired  or  stoker-fired,  should  be  at  least  twenty-four 
hours. 

STARTING  AND   STOPPING. 

The  conditions  regarding  the  temperature  of  the  furnace  and 
boiler,  the  quantity  and  quality  of  the  live  coal  and  ash  on  the 
grates,  the  water  level,  and  the  steam  pressure,  should  be  as  nearly 
as  possible  the  same  at  the  end  as  at  the  beginning  of  the  test. 

To  secure  the  desired  equality  of  conditions  with  hand-fired 
boilers,  the  following  method  should  be  employed: 

The  furnace  being  well  heated  by  a  preliminary  run,  burn  the  fire  low,  and 
thoroughly  clean  it,  leaving  enough  live  coal  spread  evenly  over  the  grate 
(say  2  to  4  ins.),*  to  serve  as  a  foundation  for  the  new  fire.  Note  quickly 
the  thickness  of  the  coal  bed  as  nearly  as  it  can  be  estimated  or  measured; 
also  the  water  level,  f  the  steam  pressure,  and  the  time,  and  record  the 
latter  as  the  starting  time.  Fresh  coal  should  then  be  fired  from  that 
weighed  for  the  test,  the  ashpit  thoroughly  cleaned,  and  the  regular  work 
of  the  test  proceeded  with. 

Before  the  end  of  the  test  the  fire  should  again  be  burned  low  and  cleaned 
in  such  a  manner  as  to  leave  the  same  amount  of  live  coal  on  the  grate 
as  at  the  start.  When  this  condition  is  reached,  observe  quickly  the  water 
level,  t  the  steam  pressure,  and  the  time,  and  record  the  latter  as  the  stop- 
ping time.  If  the  water  level  is  lower  than  at  the  beginning,  a  correction 
should  be  made  by  computation,  rather  than  by  feeding  additional  water. 
Finally  remove  the  ashes  and  refuse  from  the  ashpit. 

In  a  plant  containing  several  boilers  where  it  is  not  practicable  to  clean 
them  simultaneously,  the  fires  should  be  cleaned  one  after  the  other  as  rapidly 
as  may  be,  and  each  one  after  cleaning  charged  with  enough  coal  to  main- 

*  1  to  2  in.  for  small  anthracite  coals. 

t  Do  not  blow  down  the  water-glass  column  for  at  least  one  hour  before  these  readings 
are  taken.  An  erroneous  indication  may  otherwise  be  caused  by  a  change  of  temperature 
and  density  of  the  water  within  tha  column  and  connecting  pipe. 


568  STEAM-BOILER  ECONOMY. 

tain  a  thin  fire  in  good  working  condition.  After  the  last  fire  is  cleaned 
and  in  working  condition,  burn  all  the  fires  low  (say  4  to  6  in.),  note 
quickly  the  thickness  of  each,  also  the  water  levels,  steam  pressure,  and 
time,  which  last  is  taken  as  the  starting  time.  Likewise  when  the  time 
arrives  for  closing  the  test,  the  fires  should  be  quickly  cleaned  one  by  one, 
and  when  this  work  is  completed  they  should  all  be  burned  low  the  same 
as  at  the  start  and  the  various  observations  made  as  noted. 

In  the  case  of  a  large  boiler  having  several  furnace  doors  requiring  the 
fire  to  be  cleaned  in  sections  one  after  the  other,  the  above  directions  per- 
taining to  starting  and  stopping  in  a  plant  of  several  boilers  may  be 
followed.  . 

To  obtain  the  desired  equality  of  conditions  of  the  fire  when  a 
mechanical  stoker  other  than  a  chain  grate  is  used,  the  procedure 
should  be  modified  where  practicable  as  follows: 

Regulate  the  coal  feed  so  as  to  burn  the  fire  to  the  low  condition  required  for 
cleaning.  Shut  off  the  coal-feeding  mechanism  and  fill  the  hoppers  level 
full.  Clean  the  ash  or  dump  plate,  note  quickly  the  depth  and  condition 
of  the  coal  on  the  grate,  the  water  level,  the  steam  pressure,  and  the  time, 
and  record  the  latter  as  the  starting  time.  Then  start  the  coal-feeding 
mechanism,  clean  the  ashpit,  and  proceed  with  the  regular  work  of  the 
test. 

When  the  time  arrives  for  the  close  of  the  test,  shut  off  the  coal-feeding 
mechanism,  fill  the  hoppers  and  burn  the  fire  to  the  same  low  point  as  at 
the  beginning.  When  this  condition  is  reached,  note  the  water  level,  the 
steam  pressure,  and  the  time,  and  record  the  latter  as  the  stopping  time. 
Finally  clean  the  ash  plate  and  haul  the  ashes. 

In  the  case  of  chain  grate  stokers,  the  desired  operating  conditions  should 
be  maintained  for  half  an  hour  before  starting  a  test  and  for  a  like  period 
before  its  close,  the  height  of  the  stoker  gate  or  throat  plate  and  the 
speed  of  the  grate  being  the  same  during  both  of  these  periods. 

RECORDS. 

Half-hourly  readings  of  the  instruments  are  usually  sufficient. 
If  there  are  sudden  and  wide  fluctuations,  the  readings  in  such 
cases  should  be  taken  every  fifteen  minutes,  and  in  some  instances 
oftener. 

In  hand-fired  tests  the  coal  should  be  weighed  and  delivered  to  the  firemen  in 
portions  sufficient  for  one  hour's  run,  thereby  ascertaining  the  degree  of 
uniformity  of  firing.  An  ample  supply  of  coal  should  be  maintained  at  all 
times,  but  the  quantity  on  the  floor  at  the  end  of  each  hour  should  be  as 
small  as  practicable,  so  that  the  same  may  be  readily  estimated  and 
deducted  from  the  total  weight.  Likewise  in  stoker  tests  the  weight  of 
coal  fed  to  the  furnace  each  hour  should  be  determined. 

The  records  should  be  such  as  to  ascertain  also  the  consumption  of 
feedwater  each  hour,  and  thereby  determine  the  degree  of  uniformity  of 
evaporation. 

QUALITY    OF    STEAM. 

If  the  boiler  does  not  produce  superheated  steam  the  percentage 
of  moisture  in  the  steam  should  be  determined  by  the  use  of  a 
throttling  or  separating  calorimeter.  If  the  boiler  has  superheating 
surface,  the  temperature  of  the  steam  should  be  determined  by  the 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  569 

use  of  a  thermometer  inserted  in  a  thermometer  well  in  the  steam- 
pipe. 

SAMPLING    AND    DRYING    COAL. 

During  the  progress  of  the  test  the  coal  should  be  regularly 
sampled  for  the  purpose  of  analysis  and  determination  of  moisture. 

ASHES   AND    REFUSE. 

The  ashes  and  refuse  withdrawn  from  the  furnace  and  ash-pit 
during  the  progress  of  the  test  and  at  its  close  should  be  weighed 
so  far  as  possible  in  a  dry  state.  If  wet  the  amount  of  moisture 
should  be  ascertained  and  allowed  for,  a  sample  being  taken  and 
dried  for  this  purpose.  This  sample  may  serve  also  for  analysis 
for  the  determination  of  unburned  carbon. 

CALORIFIC    TESTS    AND    ANALYSES   OF    COAL. 

The  quality  of  the  fuel  should  be  determined  by  calorific  tests 
and  analyses  of  the  coal  sample  above  referred  to. 

ANALYSES    OF    FLUE    GASES. 

For  approximate  determinations  of  the  composition  of  the  flue 
gases,  the  Orsat  apparatus,  or  some  modification  thereof,  should 
be  employed.  If  momentary  samples  are  obtained  the  analyses 
should  be  made  as  frequently  as  possible,  say  every  15  to  30  minutes, 
depending  on  the  skill  of  the  operator,  noting  at  the  time  the 
sample  is  drawn  the  furnace  and  firing  conditions.  If  the  sample 
drawn  is  a  continuous  one,  the  intervals  may  be  made  longer. 

SMOKE    OBSERVATIONS. 

In  tests  of  bituminous  coals  requiring  a  determination  of  the 
amount  of  smoke  produced,  observations  should  be  made  regularly 
throughout  the  trial  at  intervals  of  five  minutes  (or  if  necessary 
every  minute),  noting  at  the  same  time  the  furnace  and  firing 
conditions. 

For  observations  covering  a  period  of  one  or  more  single  firings,  the  inter- 
vals should  be  quarter  minutes. 

CALCULATION    OF    RESULTS. 

(a)  Corrections  for  Quality  of  Steam.  When  the  percentage  of  moisture  is  less 
than  2  per  cent  it  is  sufficient  merely  to  deduct  the  percentage  from  the 
weight  of  water  fed,  in  which  case  the  factor  of  correction  for  quality  is 

%  moisture 
100        ' 


570  STEAM-BOILER  ECONOMY. 


When  the  percentage  is  greater  than  2  per  cent,  or  if  extreme  accuracy 
is  required,  the  factor  of  correction  is 


in  which  P  is  the  proportion  of  moisture,  H  the  total  heat  of  1  Ib.  of  satu- 
rated steam,  hi  the  heat  in  water  at  the  temperature  of  saturated  steam, 
and  h  the  heat  in  water  at  the  feed  temperature. 

When  the  steam  is  superheated  the  factor  of  correction  for  quality  of 
steam  is 

Hs-h 

H  -h' 

in  which  Hs  is  the  total  heat  of  1  Ib.  of  superheated  steam  of  the  observed 
temperature  and  pressure. 

Unless  otherwise  provided,  a  combined  boiler  and  superheater  should 
be  treated  as  one  unit,  and  the  equivalent  of  the  work  done  by  the  super- 
heater should  be  included  in  the  evaporative  work  of  the  boiler. 

(6)  Correction  for  Steam  or  Power  usec,  for  Aiding  Combustion.  The  quantity  of 
steam  or  power,  if  any,  used  for  producing  draft,  injecting  fuel,  or  aiding 
combustion,  should  be  determined  and  recorded  in  the  Table  of  Data  and 
Results.  There  should  also  be  recorded,  by  foot-note  below  the  table,  a 
statement  showing  whether  or  not  a  deduction  has  been  made  from  the  total 
evaporation  for  steam  or  power  used,  and  if  such  deduction  has  been  made, 
the  method  of  computing  it. 

(c)  Equivalent  Evaporation.  The  equivalent  evaporation  from  and  at  212° 
is  obtained  by  multiplying  the  weight  of  water  evaporated,  corrected  for 
moisture  in  steam,  by  the  "  factor  of  evaporation."  The  latter  equals 

H-h 


970.4 ' 

in  which  H  and  h  are  respectively  the  total  heat  of  saturated  steam  and 
of  the  feedwater  entering  the  boiler. 

The  "  factor  of  evaporation  "  and  the  "  factor  of  correction  for  quality 
of  steam  "  may  be  combined  into  one  expression  in  the  case  of  superheated 
steam  as  follows: 

Hs-h       • 
970.4  ' 

(d)  Efficiency.  The  "  efficiency  of  boiler,  furnace  and  grate  "  is  the  relation 
between  the  heat  absorbed  per  pound  of  coal  as  fired,  and  the  calorific  value 
of  1  Ib.  of  coal  as  fired. 

The  "  efficiency  based  on  combustible  "  is  the  relation  between  the 
heat  absorbed  per  pound  of  combustible  burned  and  the  calorific  value 
of  1  Ib.  of  combustible.  This  expression  of  efficiency  furnishes  an  approx- 
imate means  for  comparing  the  results  of  different  tests  when  the  losses 
of  unburned  coal  due  to  grates,  cleanings,  etc.,  are  eliminated. 

The  "  combustible  burned "  is  determined  by  subtracting  from  the 
weight  of  coal  supplied  to  the  boiler,  the  moisture  in  the  coal,  the  weight 
of  ash  and  unburned  coal  withdrawn  from  the  furnace  and  ashpit,  and  the 
weight  of  dust,  soot,  and  refuse,  if  any,  withdrawn  from  the  tubes,  flues, 
and  combustion  chambers,  including  ash  carried  away  in  the  pases,  if  any, 
determined  from  the  analyses  of  coal  and  ash.*  The  "combustible"  used 
for  determining  the  calorific  value  is  the  weight  of  coal  less  the  moisture 
and  ash  found  by  analysis. 

*In  cases  of  high  rates  of  combustion  the  determination  of  the  combustible  burned  may  be  subject 
to  considerable  error  on  account  of  the  loss  of  cinders,  soot  and  unburned  fuel  which  are  blown  to  waste. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  571 

» 

The  "  heat  absorbed  "  per  pound  of  coal  or  combustible  is  calculated 
by  multiplying  the  equivalent  evaporation  from  and  at  212°  per  pound 
of  coal  or  combustible  by  970.4. 

(e)  Heat  Balance.  A  "  heat  balance,"  or  approximate  distribution  of  the 
calorific  value  of  1  Ib.  of  dry  coal  among  the  several  items  of  heat  util- 
ized and  heat  lost,  should  be  obtained  in  cases  where  the  flue  gases  have 
been  analyzed  and  a  complete  analysis  made  of  the  coal. 

The  loss  due  to  moisture  in  the  coal  is  found  by  multiplying  the  total 
heat  of  1  Ib.  of  superheated  steam  at  the  temperature  of  the  escaping 
gases,  calculated  from  the  temperature  of  the  «ir  in  the  boiler  room,  by  the 
proportion  of  moisture/freferred  to  dry  coal. 

The  loss  due  to  moisture  formed  by  the  burning  of  hydrogen  is  obtained 
by  multiplying  the  total  heat  of  1  Ib.  of  superheated  steam  at  the  tem- 
perature of  the  escaping  gases,  calculated  from  the  temperature  of  the  air 
in  the  boiler  room,  by  the  proportion  of  the  hydrogen,  determined  from 
the  analysis  of  the  coal,  referred  to  dry  coal,  and  multiplying  the  result  by  9. 

The  loss  due  to  heat  carried  away  in  the  dry  gases  is  found  by  multi- 
plying the  weight  of  gas  per  pound  of  dry  coal  by  the  elevation  of  tem- 
perature of  the  gases  above  the  temperature  of  the  boiler  room,  and  by 
the  specific  heat  of  the  gases  (0.24).  The  weight  of  gas  per  Ib.  of  dry 
coal  is  obtained  by  finding  the  weight  of  dry  gas  per  pound  of  carbon 
burned,  using  the  formula 

11  CO2+8O+7(CO+N) 
3(CO2+CO) 

in  which  CO2,  CO,  O,  and  N  are  expressed  in  percentages  by  volume,  and 
multiplying  this  result  by  the  proportion  borne  by  the  carbon  burned 
to  the  whole  amount  of  dry  coal  as  determined  from  the  results  of  the 
analysis  of  the  coal,  ash,  and  refuse. 

The  loss  due  to  incomplete  combustion  of  carbon  is  found  by  first  obtain- 
ing the  proportion  borne  by  the  carbon  monoxide  in  the  gases  to  the  sum 
of  the  carbon  monoxide  and  carbon  dioxide,  and  then  multiplying  this 
proportion  by  the  proportion  of  carbon  in  the  coal  minus  the  carbon  lost 
in  the  ash  and  refuse,  and  finally  multiplying  the  product  by  10,150, 
which  is  the  number  of  heat  units  generated  by  burning  to  carbon  dioxide 
one  pound  of  carbon  contained  in  carbon  monoxide. 

The  loss  due  to  combustible  matter  in  the  ash  and  refuse  is  found  by 
multiplying  the  proportion  that  this  combustible  bears  to  the  whole  amount 
of  dry  coal  by  its  calorific  value  per  pound.  For  most  purposes  it  is  suf- 
ficient to  assume  the  latter  to  be  14,600  B.T.U.,  the  same  as  that  of  carbon. 

The  loss  due  to  moisture  in  the  air  is  determined  by  multiplying  the 
weight  of  such  moisture  per  pound  of  dry  coal  by  the  elevation  of  tempera- 
ture of  the  flue  gases  above  the  temperature  of  the  boiler  room  and  by 
0.47.  The  weight  of  moisture  is  found  by  multiplying  the  weight  of  air 
per  pound  of  dry  coal  by  the  moisture  in  one  pound  of  air  determined  from 
readings  of  the  wet  and  dry-bulb  thermometer. 

(/)  Total  Heat  of  Combustion  of  Coal,  by  Analysis.  The  total  heat  of  com- 
bustion may  be  computed  from  the  results  of  the  ultimate  analysis  by 
using  the  formula  ~* 


14,600  C  +62,000  fa  ~) +4000  S, 


in  which  C,  H,  O,  and  S  refer  to  the  proportions  of    carbon,    hydrogen' 
oxygen,  and  sulphur,  respectively. 

(g)  Air  for  Combustion.     The  quantity  of  air  used  may  be  calculated  by  the 
formulae : 

3.032  N 
Lb.  of  air  per  Ib.  of  carbon  =  /^, 


572  STEAM-BOILER  ECONOMY. 

in  which  N,  CO2  and  CCTare  the  percentages  of  dry  gas  obtained  by  analysis 
and 

Lb.  of  air  per  Ib.  of  coal  =  lb.  air  per  Ib.  CX(per  cent  C  in  the  coal,  less 
per  cent  carbon  in  refuse,  referred  to  coal). 

The  ratio  of  the  air  supply  to  that  theoretically  required  for  complete 
combustion  is 


DATA    AND    KESULTS. 


The  data  and  results  should  be  reported  in  accordance  with 
the  form  printed  below,  adding  lines  for  data  not  provided  for, 
or  omitting  those  not  required,  as  may  conform  to  the  object  in  view. 


CHART. 

In  trials  having  for  an  object  the  determination  and  exposition 
of  the  complete  boiler  performance,  the  entire  log  of  readings  and 
data  should  be  plotted  on  a  chart  and  represented  graphically. 

TESTS   WITH    OIL    AND    GAS    FUELS. 

Tests  of  boilers  using  oil  or  gas  for  fuel  should  accord  with  the 
rules  here  given,  excepting  as  they  are  varied  to  conform  to  the 
particular  characteristics  of  the  fuel.  The  proper  length  of  tests 
with  gas  and  oil  fuels  may  be  determined  by  a  consideration  of  the 
probable  errors  and  the  degree  of  accuracy  desired,  the  minimum 
duration  for  economy  tests  being  5  hours.  With  these  fuels  the 
"  flying  "  method  of  starting  and  stopping  is  employed. 

The  table  of  data  and  results  should  contain  items  stating  character  of  furnace 
and  burner,  quality  and  composition  of  oil  or  gas,  temperature  of  oil,  and 
data  regarding  the  performance  of  the  apparatus  supplying  the  fuel. 

DATA  AND   RESULTS  OF  EVAPORATIVE  TEST.* 

1.  Test  of.  .To  determine.  .  .  .Test  conducted  by.  .boiler  located  at.  . 

2.  Number  and  kind  of  boilers  ................................. 

3.  Kind  of  furnace  ........................................... 

4.  Grate  surface  (width  ........  length  ........  )  ..................      Sq.  ft. 

5.  Water  heating  surface  ....................................... 

6.  Superheating  surface  ........................................ 

7.  Total  heating  surface  ......  ....  .....................  ......... 

d.  Volume  of  combustion  space  between  grate  and  heating  surface         " 

e.  Distance  from  center  of  grate  to  nearest  heating  surface  .....        ft. 

(Date,  Duration,  etc. 

8.  Date  ............................  ................  .  ......... 

9.  Duration.  .  .........................  ..............  ........  .      Hrs. 

10.  Kind  and  size  of  coal  ........................................ 

*  This  table  contains  the  principal  items  of  the  table  in  the  Code  of  1915  of  the  A.S.M.E 
Committee  on  Power  Tests. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  573 

Average  Pressures,  Temperatures,  etc. 

11.  Steam  pressure  by  gage Lbs. 

12.  Temperature  of  steam,  if  superheated , .  Deg. 

13.  Temperature  of  feed  water  entering  boiler 

14.  Temperature  of  escaping  gases  leaving  boiler " 

15.  Force  of  draft  between  damper  and  boiler In. 

c.  Draft  in  furnace 

d.  Draft  or  blast  in  ash  pit " 

16.  State  of  weather 

a.  Temperature  of  external  air Deg. 

6.  Temperature  of  air* entering  ash  pit " 

c.  Relative  humidity  of  air  entering  ash  pit " 

Quality  of  Steam. 

17«.  Percentage   of  moisture   in  steam  or  degrees   of  super- 
heating      Per  cent  or  deg. 

18.  Factor  of  correction  for  quality  of  steam 

Total  Quantities. 

19.  Total  weight  of  coal  as  fired  * Lbs. 

20.  Percentage  of  moisture  in  coal  as  fired Per  cent 

21.  Total  weight  of  dry  coal  fired Lbs. 

22.  Total  ash,  clinkers,  and  refuse  (dry)f 

23.  Total  combustible  burned  (Item  21  -Item  22) 

24.  Percentage  of  ash  and  refuse  in  dry  coal Per  cent 

25.  Total  weight  of  water  fed  to  boiler  J Lbs. 

26.  Total  water  evaporated,   corrected  for  quality  of  steam   (Item 

25Xltem  18).. Lbs. 

27.  Factor  of  evaporation  based  on  temperature  of  water  entering  boiler. 

28.  Total  equivalent  evaporation  from  and  at  212°  (Item  26  X Item  27)       Lbs. 

Hourly  Quantities  and  Rates. 

29.  Dry  coal  per  hour Lbs. 

30.  Dry  coal  per  square  foot  of  grate  surface  per  hour 

31.  Water  evaporated  per  hour,  corrected  for  quality  of  steam 

32.  Equivalent  evaporation  per  hour  from  and  at  212°  § 

33.  Equivalent  evaporation  per  hour  from  and  at  212°  per  square  foot 

of  water  heating  surface* 

Capacity. 

34.  Evaporation  per  hour  from  and  at  212°  (same  as  Item  32) Lbs. 

a.  Boiler  horsepower  developed  (Item  34-^34|) Bl.  H.P. 

35.  Rated  capacity  per  hour,  from  and  at  212° Lbs. 

a.  Rated  boiler  horsepower Bl.  H.P. 

36.  Percentage  of  rated  capacity  developed Per  cent 

Economy. 

37.  Water  fed  per  pound  of  coal  as  fired  (Item  25  -5- Item  19) Lbs. 

38.  Water  evaporated  per  pound  of  dry  coal  (Item  26 -^  Item  21) 

*  The  term  "as  fired"  means  actual  conditions  including  moisture.  Weight  corrected  fo 
estimated  difference  in  weight  of  coal  on  the  grate  at  beginning  and  end. 

t  Corrected  when  practicable  for  dust,  soot,  etc. 

t  Corrected  for  inequality  of  water  level  and  of  steam  pressure  at  beginning  and  end. 

§  The  symbol  "U.  E."  meaning  Units  of  Evaporation,  may  be  substituted  for  the  expres- 
sion, Equivalent  evaporation  from  and  at  212°. 


574 


STEAM-BOILER  ECONOMY. 


39.  Equivalent  evaporation  from  and  at  212°  per  pound  of  coal  as 
fired  (Item  28^Item  19) 

10.  Equivalent  evaporation  from  and  at  212°  per  pound  of  dry  coal 

(Item  28^-Item  21) 

11.  Equivalent  evaporation  from  and  at  212°  per  pound  of  combustible 

(Item  28  4- Item  23) 


Efficiency. 

42.  Calorific  value  of  1  Ib.  of  dry  coal  by  calorimetej  *. .  . 

a.  Calorific  value  of  1  Ib.  dry  coal  by  analysis 

43.  Calorific  value  of  1  Ib.  of  combustible  by  calorimeter. 

a.  Calorific  value  of  1  Ib.  combustible  by  analysis.. 

44.  Efficiency  of  boiler,  furnace  and  grate, 


B.T.U. 


100  X 


Item  40X970.4 


Item  42 


45.  Efficiency  based  on  combustible. 


100X 


Item  41  X970.4 
Item  43 


Cost  of  Evaporation. 

46.  Cost  of  coal  per  ton  of  ....  Ibs.  delivered  in  boiler  room Dollars 

47.  Cost  of  coal  required  for  evaporation  1000  Ibs.    of  water  under 

observed  conditions 

48.  Cost  of  coal  required  for  evaporating  1000  Ibs.  of  water  from 

and  at  212°.. 


Smoke  Data. 
49.  Percentage  of  smoke  as  observed 


Per  cenl 


Firing  Data. 

50.  Kind  of  firing,  whether  spreading,  alternate,  or  coking 

c.  Average  interval  between  times  of  leveling  or  breaking  up.  .  .       Min. 

51.  Analysis  of  dry  gases  by  volume: 

a.  Carbon  dioxide  (CO?) Per  cent 

b.  Oxygen  (O) 

c.  Carbon  monoxide  (CO) 

d.  Hydrogen  and  hydrocarbons 

e.  Nitrogen,  by  difference  (N) " 

52.  Proximate  analysis  of  coal  ^ 


a.  Moisture 

6.  Volatile  matter 

c.  Fixed  carbon 

d.  Ash 


As  Fired. 

Dry  Coal. 

Combustible. 

100% 

100% 

100% 

e.  Sulphur,  separately  determined 


If  the  calorific  value  is  desired  per  Ib.  of  coal  "  as  fired,"  multiply  by    100  —Item  20)  -j- 100. 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


575 


53.  Ultimate  analysis  of  dry  coal. 

a.  Carbon  (C) Per  cent 

b.  Hydrogen  (H)    

c.  Oxygen  (O) 

d.  Nitrogen  (N) 

e.  Sulphur  (S) 

/.   Ash 


54.  Analysis  of  Ash  and  Refuse,  etc 


55. 


coal  and  combustible 
boiler    (Item   40   or 


Heat  balance,  based  on  dry 
a.  Heat    absorbed    by    th 

41  X970.4) 
6.  Loss  due  to  evaporation  of  moisture  in  coal  .  .  . 

c.  Loss  due  to  heat  carried  away  by  steam  formed 

by  the  burning  of  hydrogen 

d.  Loss  due  to  heat  carried  away  in  the  dry  flue 


Loss  due  to  carbon  monoxide 

Loss  due  to  combustible  in  ash  and  refuse 

Loss  due  to  heating  moisture  in  air 

Loss  due  to  unconsumed  hydrogen  and  hydro- 
carbons, to  radiation,  and  unaccounted  for .  . 

Total  calorific  value  of  1  Ib.  of  dry  coal. 
(Item  42.) 


Dry  Coal. 


B.T.U. 


100 


If  it  is  desired  that  the  heat  balance  be  based  on  coal  "  as  fired,"  or  on  "  com- 
bustible burned,"  the  items  in  the  first  column  are  multiplied  by  the  proportion 
(100 -Item  20) -H  100  for  coal  "as  fired,"  or  by  100-7- (100 -Item  55/,  per  cent) 
for  "combustible." 


PRINCIPAL  DATA  AND  RESULTS  OF  BOILER  TEST. 


1.  Grate  surface  (width length 

2.  Total  heating  surface 

3.  Date.. 


4.  Duration 

5.  Kind  and  size  of  coal 

6.  Steam  pressure  by  gage 

7.  Temperature  of  feed  water  entering  boiler 

8.  Percentage  of  moisture  in  steam  or  number  of  degrees  of  super- 

heating   

9.  Percentage  of  moisture  in  coal 

10.  Dry  coal  per  hour 

1 1 .  Dry  coal  per  square  foot  of  grate  surface  per  hour 

12.  Equivalent  evaporation  per  hour  from  and  at  212° 

13.  Equivalent  evaporation  per  hour  from  and  at  212°  per  square  foot 

of  heating  surface 

14.  Rated  capacity  per  hour,  from  and  at  212° 

15.  Percentage  of  rated  capacity  developed 

16.  Equivalent  evaporation  from  and  at  212°  per  pound  of  dry  coal.  . 

17.  Equivalent  evaporation  from  and  at  21 2°  per  pound  of  combustible 


l.ft 


Hrs. 

Lbs. 
Deg. 

Per  cent 

or  deg. 

Per  cent 

Lbs. 


Per  cent 
Lbs. 


576  STEAM-BOILER  ECONOMY. 

18.  Calorific  value  of  1  Ib.  of  dry  coal  by  calorimeter  ...............     B.T.U. 

19.  Calorific  value  of  1  Ib.  of  combustible  by  calorimeter  ............          " 

20.  Efficiency  of  boiler,  furnace,  and  grate 

1nnx/Iteml6X  970.4 

Item.18       '  PerC6nt 

21.  Efficiency  based  on  combustible 

Item  17X970.4 
100X        Item  19        •  Percent 

LOCATION    OP    INSTRUMENTS   FOR   BOILER  'TESTS.* 

The  feedwater  thermometer  should  be  placed  in  a  thermometer  well  and 
inserted  in  the  feed  pipe.  Where  an  injector  is  employed,  and  the  water  is 
weighed  or  measured  before  it  is  supplied  thereto,  the  well  should  be  placed 
on  the  suction  side  of  the  injector,  and  the  injector  should  receive  steam  through 
a  short  covered  pipe  connected  directly  to  the  boiler  under  test.  If  the  steam 
is  taken  from  some  other  source  and  it  is  of  different  pressure  and  different 
quality  from  that  of  the  boiler  under  test,  correction  should  be  made  for  such 
difference.  When  the  temperature  of  the  water  changes  between  the  injector 
and  boiler,  as  by  the  use  of  a  heater  or  by  excessive  radiation,  the  temperature 
at  which  the  water  enters  and  leaves  the  injector  and  that  at  which  it  enters 
the  boiler  should  all  be  taken.  In  that  case,  the  weight  to  be  used  is  that  of  the 
water  leaving  the  injector,  computed  from  the  heat  units  if  not  directly 
measured,  and  the  temperature  that  of  the  water  entering  the  boiler.  The  weight 
of  condensed  steam  to  be  added  to  the  weight  of  water  entering  the  injector, 
to  obtain  that  leaving  the  injector,  may  be  computed  by  multiplying  the  weight 
entering  by  the  proportion 


h-hj 

in  which 

hi  =heat  units  per  Ib.  of  water  entering  injector; 
/i2  =  heat  units  per  Ib.  of  steam  entering  injector; 
-  hz  =  heat  units  per  Ib.  of  water  leaving  injector. 

The  location  of  the  steam  calorimeter  and  steam  thermometer  should  be 
as  close  to  the  boiler  as  possible. 

Draft  gages  should  be  attached  to  each  boiler  between  the  hand  damper 
and  the  boiler,  and  as  near  the  damper  as  practicable.  In  the  case  of  a  plant 
containing  a  number  of  boilers,  a  gage  should  also  be  attached  to  the  main 
flue  between  the  regulating  damper  and  the  boiler  plant.  It  is  desirable  also 
to  have  gages  connected  to  the  furnace  or  furnaces  of  the  boilers,  and  in  cases 
of  forced  blast,  to  the  ashpits  and  blower  ducts.  If  there  is  an  economizer 
in  the  flue  a  gage  should  be  connected  to  the  flue  at  each  end  of  this  apparatus. 
The  same  draft  gage  may  be  used  for  all  the  points  noted,  provided  suitable 
pipes  are  run  from  the  gage  to  each,  arranged  so  as  to  be  readily  connected  to 
either  point  at  will. 

The  flue  thermometer  should  be  located  where  it  will  show  the  average 
temperature  of  the  whole  body  of  gas.  For  an  extremely  large  flue  the  ther- 
mometer may  be  placed  in  an  oil  pot  of  small  diameter,  which  is  suspended  in 
the  flue,  and  the  thermometer  lifted  partially  out  of  the  oil  when  the  tempera- 
ture is  read.f 

*  This  and  seven  following  articles  are  condensed  from  the  Appendix  to  the  Code  of  1915 
t  When  electric  pyrometers  with  thermo-couples  are  used,  wires    may  be  run  from  several 

couples,   located  at  different  points  in  the  boilers  or  flues,     to  a  single  reading  instrument, 

provided  with  a  multiple  switch.  —  W.  K. 


EVAPORATION   TESTS  OF  STEAM-BOILERS.  577 

BITUMINOUS   COAL    SIZES. 

Bituminous  coals  in  the  Eastern  States  may  be  graded  and  sized  as  follows: 

(A)  Run  of  mine  coal;   the  unscreened  coal  taken  from  the  mine. 

(B)  Lump  coal;    that  which  passes  over  a  bar-screen  with  openings  lj  in. 
wide. 

(C)  Nut  coal;   that  which  passes  through  a  bar-screen  with  l^-in.  openings 
and  over  one  with  f-in.  openings. 

(D)  Slack  coal;   that  which  passes  through  a  bar-screen  with  f-in.  openings. 
Bituminous  coals  in  the  Western  States  may  be  graded  and  sized  as  follows: 

(E)  Run  of  mine  coal;  the  unscreened  coal  taken  from  the  mine. 

(F)  Lump  coal;    divided  into  6-in.,  3-in.  and   1|  in.  lump,  according  to 
the  diameter  of  the  circular  openings  over  which  the  respective  grades  pass; 
also  6  by  3  lump  and  3  by  lj  lump,  according  as  the  coal  passes  through  a  cir- 
cular opening  having  the  diameter  of  the  larger  figure  and  over  that  of  the 
smaller  diameter. 

(GO  Nut  coal;  divided  into  3-in.  steam  nut,~which  passes  through  an  open- 
ing 3-in.  diameter  and  over  li-m.;  Ij-in.  nut,  which  passes  through  a  H-in. 
diameter  opening  and  over  a  f-in.  diameter  opening;  f-in.  nut,  which  passes 
through  a  f-in.  diameter  opening  and  over  a  f-in.  diameter  opening. 

(H)  Screenings:   that  which  passes  through  a  lj-m.  diameter  opening. 

(/)  Washed  sizes;  those  passing  through  or  over  the  circular  openings  of 
the  following  diameters,  in  inches : 


Number                                   Through 

1                                  3 

2.                                 V, 

3.     .                             1 

4  * 

5..  . 

WATER    GLASS   TESTS   OF    LEAKAGE. 

To  determine  the  leakage  of  steam  and  water  from  a  boiler  and  steam 
pipes,  etc.,  the  water-glass  method  may  be  satisfactorily  employed.  This 
consists  of  shutting  off  all  the  feed  valves  (which  must  be  known  to  be  tight) 
and  the  main  feed  valve,  thereby  stopping  absolutely  the  entrance  or  exit  of 
water  at  the  feed  pipes  to  the  boiler;  then  maintaining  the  steam  pressure 
(by  means  of  a  very  slow  fire)  at  a  fixed  point,  which  is  approximately  that  of 
the  working  pressure,  and  observing  the  rate  at  which  the  water  falls  in  the 
gage  glasses.  It  is  well,  in  this  test,  as  in  other  work  of  this  character,  to  make 
observations  every  ten  minutes,  and  to  continue  them  for  such  length  of  time 
that  the  differences  between  successive  readings  attain  a  constant  rate.  It 
is  usually  sufficient  to  continue  the  test  for  two  hours,  thereby  obtaining  a 
number  of  half-hourly  periods.  The  quantity  of  leakage  is  ascertained  by  cal- 
culating the  volume  of  water  which  has  disappeared,  using  the  area  of  the  water 
level  and  the  depth  shown  on  the  glass,  making  due  allowance  for  the  weight 
of  one  cubic  foot  of  water  at  the  observed  pressure.  The  water  columns  should 
not  be  blown  down  during  the  time  a  water-glass  test  is  going  on,  nor  for  a  period 
of  at  least  one  hour  before  it  begins. 

CALIBRATING   WATER    METERS. 

Referring  to  Fig.  245,  two  tees  A  and  B  are  placed  in  the  feed  pipe,  and 
between  them  two  valves  C  and  D.  The  meter  is  connected  between  the  out- 
lets of  the  tees  A  and  B  and  the  valves  E  and  F  are  placed  one  on  each  side 
of  the  meter.  When  the  meter  is  running,  the  valves  E  and  F  are  opened,  and 
the  valves  C  and  D  closed.  A  small  bleeder  G  is  kept  open  to  make  sure  that 
there  is  no  leakage.  A  gage  is  attached  at  H.  When  the  meter  is  tested,  the 


578 


STEAM-BOILER  ECONOMY. 


valves  C,  D,  and  F  are  closed,  and  the\valves  E  and  7  are  opened.  The  water 
flows  from  the  valve  /  to  a  tank  on  platform  scales.  In  testing  the  meter, 
the  water  is  throttled  at  the  valve  /  to  obtain  the  desired  rate  of  discharge, 

the  gage  meanwhile  show- 
ing the  working  pressure. 
The  piping  leading  from  the 
valve  /  to  the  tank  is  ar- 
ranged with  a  swinging 
joint,  consisting  merely  of 
a  loosely  fitting  elbow,  so 
that  it  can  be  readily  turned 
into  the  tank  or  away  from 
it.  When  the  desired  speed 
has  been  secured,  the  end 
of  the  pipe  is  swung  into 
the  tank  at  the  instant  the 
pointer  of  the  meter  is  op- 
posite some  graduation  mark 
on  the  dial.  When  the  re- 
quired number  of  cubic  feet 
are  discharged,  the  pipe  is 
swung  away.  The  tests 
should  start  and  stop  at  the 
same  graduation  mark  on  the  first  dial,  and  continued  until  at  least  10  or  20 
cu.ft.  are  discharged  for  one  test.  The  tank  is  weighed  before  and  after  filling. 
The  water  passing  the  meter  should  always  be  under  pressure  so  that  any 
air  in  the  meter  may  be  discharged  through  the  vents  provided  for  this  pur- 
pose, Care  should  be  taken  that  there  is  no  unnecessary  air  drawn  into  the 
feed  water.  The  meter  should  be  tested  before  and  after  the  trial,  and  repeated 
calibrations  should  be  made  to  obtain  confirmative  results. 


FIG.  245. — CALIBRATING  WATER  METERS. 


GAS    ANALYSIS. 

Orsat  Apparatus.     The  Orsat  apparatus  is  a  portable  instrument  contained 
in  a  wooden  case  with  removable  sliding  doors  front  and  back,  as  shown  in  its 
simplest  form  in  Fig.  246.    It  consists  essentially  of  a  measuring  tube  or  burette, 
three  absorbing  bottles  or  pipettes,  and  a  level- 
ing bottle,  together  with  the  connecting  tubes 
and  apparatus.    The  bottle  and  measuring  tube 
contain   pure   water;    the  first  pipette,  sodium 
or  potassium  hydrate  dissolved   in  three  times 
its  weight  of  water;  the  second,  pyrogallic  acid 
dissolved  in  sodium  hydrate  in  the  proportion  of 
5  grams  of  the  acid  to  100  c.c.  of  the  hydrate; 
and  the  third,  cuprous  chloride. 

The  manipulation  of  the  instrument  is  as 
follows: 

After  completely  drawing  out  the  air  con- 
tained in  the  supply  pipe,  a  sample  of  the  gas 
is  drawn  into  the  measuring  tube  by  opening  the 
necessary  connections  and  allowing  the  water  to 
empty  itself  from  the  tube  and  flow  into  the 
bottle.  The  quantity  of  gas  drawn  in  is  adjusted 
to  100  cc.  By  opening  one  by  one  the  con- 
nections to  the  pipettes,  and  raising  and  lower- 
ing the  water  bottle,  the  sample  is  alternately 
admitted  to  and  withdrawn  from  the  pipettes, 
and  the  ingredients  one  by  one  absorbed. 

The  first  pipette  absorbs  CO2;  the  second,  O;  and  the  third,  CO.     The  quan- 
tity absorbed  in  each  case  is  determined  by  returning  the  sample  to  the  measur- 


F      94fi 
*IG-246- 


APPARATUS 


EVAPORATION    TESTS  OF  STEAM-BOILERS. 


579 


D 


ing  burette  and  reading  the  volume.  The  percentage  of  CO2  is  read  directly 
being  the  first  absorption.  This  of  the  other  two  ingredients  are  the  respectiva 
differences  between  the  readings  taken  after  successive  absorptions. 

Various  modifications  of  this  apparatus  have  been 
developed  which  enable  analyses  to  be  made  with  greater 
rapidity  than  with  the  form  illustrated. 

Hempel  Apparatus.  The  Hempel  apparatus  works 
on  the  same  principle  as  the  Orsat,  except  that  the 
absorption  may  be  hastened  by  shaking  the  pipette 
bodily,  bringing  the  chemical  into  most  intimate  con- 
tact with  the  gas.  It  is  less  portable  and  in  some 
particulars  it  requires  more  careful  manipulation  than 
the  Orsat. 

The  absorption  pipettes  are  made  in  sets  which  are 
shaped  in  the  form  of  globes,  and  a  riumber  of  inde- 
pendent sets  are  required  for  the  treatment  of  the  dif- 
ferent constituent  gases.*  A  sample  pipette  of  the 
Hempel  type  is  shown  in  Fig.  247.  FIG.  247.  HEMPEL 

PIPETTE. 


FURNACE    EFFICIENCY. 

Attempts  have  been  made  to  separate  the  combined  efficiency  of  boiler, 
furnace,  and  grate  into  two  parts,  viz.,  efficiency  due  to  boiler  alone,  and 
efficiency  due  to  furnace  (including  grate),  but  there  is  no  agreement  as  to  the 
exact  line  of  demarcation  to  be  used  in  separating  one  from  the  other. 

The  heat  losses  chargeable  to  the  furnace  alone  are  clearly  those  designated 
a,  6,  c  and  d  in  the  following  list: 

a.  The  loss  due  to  unburned  solid  fuel  dropping  through  the  grates  or 

withdrawn  from  the  furnace,  including  the  solid  combustible  matter 
in  the  cinders,  sparks,  flue  dust,  etc. 

b.  Loss  due  to  the  production  of  CO  instead  of  CO2. 

c.  Loss  due  to  escape  of  unburned  volatile  hydrocarbons. 

d.  Loss  .due  to  the  combination  of  carbon  and  moisture  and  production  of 

hydrogen  (by  the  reaction  C+H2O=CO+2H)  when  fresh  moist  coal 
is  thrown  on  a  bed  of  white  hot  coke. 

The  remaining  heat  losses,  which  are  those  due  to  heat  carried  away  by  the 
air  and  moisture  in  the  escaping  gases,  loss  from  radiation,  and  losses  unaccounted 
for,  may  be  divided  as  given  below  in  Items  e  to  j. 

e.  Moisture    losses;     embracing   evaporation    of   moisture    and    heating   of 

steam   thus   formed   to    Tp(Tp  =  temperature   corresponding  to   boiler 
pressure). 

1.  Moisture  in  coal. 

2.  'air. 

3.  ' '         due  to  burning  of  hydrogen  in  the  fuel. 

/.   Moisture  losses,  consisting  in  the  further  heating  of  steam  of  Item  3 
from  Tp  to  Tg(Tg  =  temperature  of  escaping  gases). 

1.  Moisture  in  coal. 

2.  "  air. 

3.  "      due  to  H. 
g.  Theoretical  air  supply  losses. 

1.  Heated  to  Tp. 

2.  "      from  TP  to  TV"! 
h.  Excess  air  supply  losses. 

1.  Heated  to  TP. 

2.  "       from  Tp  to  T0. 


*  For  description  of  the  Hempel  apparatus  and  the   method  of   operating  it,  see  Hempel' s 
Gas  Analysis,  translated  by  L.  M.  Dennis. 


580  STEAM-BOILER  ECONOMY. 

i.   Radiation. 

1.  Due  to  furnace. 

2.  '  '      boiler. 
j.   Unaccounted  for  losses. 

1.  Due  to  furnace. 

2.  '  '       boiler. 

It  has  been  suggested  that  these  losses  be  grouped  and  apportioned  as 
follows: 

U  =  unavoidable  losses  =  e\  +  62  +  ^  -f-  g\  ', 

F  =  furnace  losses  =  a  +b  -f-c  +d  -Hi  -f  ji  5 

B  =  boiler  losses  =fi+fa+fa+g*+hi+h 
in  which  case  the  individual  efficiencies  are 

Maximum  theoretical  efficiency  =  —  __     ; 

100-(!7+F) 
Furnace  efficiency  =  —       _  .  .  —  -; 

WQ-(U+F+B) 
Boiler  efficiency^     m-(U+F)     ; 

Combined  efficiency  of  boiler,  furnace  and  grate  =  —     —  r^  --  -. 

These  formulae  do  not  however  furnish  a  method  of  determining  the  true 
individual  efficiencies  desired,  because  it  is  impossible  to  determine  Item  d, 
and  impracticable  to  obtain  Item  c  with  the  gas-testing  appliances  ordinarily 
available.  It  is  impossible  also  to  separate  the  losses  i\  and  j\  attributed  to  the 
furnace,  from  the  boiler  losses  alone  due  to  radiation  and  those  unaccounted  for. 

Another  suggestion  is  to  transfer  the  excess  air  loss  hi  to  the  group  of  furnace 
losses  F;  but  this  makes  the  matter  even  worse,  inasmuch  as  the  furnace  effic- 
iency is  then  dependent  on  the  steam  pressure  in  the  boiler,  which  is  a  matter 
foreign  to  any  furnace  condition.  It  further  assumes  that  the  flue  gases  cannot 
be  cooled  below  the  temperature  due  to  the  pressure,  which  although  true  for 
many  types  of  boiler,  is  not  true  in  cases  where  the  contra-flow  principle  is 
used. 

A  third  method  suggested  is  to  include  among  the  boiler  losses  all  those 
which  have  been  classed  as  unavoidable  above.  By  this  method  the  furnace 
efficiency  is 

100  -F 
100    ' 
and  the  boiler  efficiency 


100  -F 

If  it  is  desired  to  divide  the  combined  efficiency  between  boiler  and  furnace 
in  some  such  manner  as  those  suggested,  the  method  of  division  employed 
should  be  clearly  stated. 

CALCULATION  OF  HEAT  BALANCE  FOR  BOILER  TEST. 

The  following  example  shows  the  method  to  be  employed  in  computing 
the  various  quantities  in  the  heat  balance  table. 

Data.  —  Semi-bituminous   coal,    2%   moisture,   8%   ash,    90%   combustible, 

82%  C,  4%  H,  3%  O,  1%  N. 

B.T.U.  per  Ib.  combustible  15,800;  per  Ib.  coal  as  fired,  14,220. 
Ash  and  refuse  by  boiler  test,  13%,  referred  to  coal  as  fired.  The 
13%  ash  and  refuse  is  assumed  to  contain  the  8%  of  ash  shown 
by  the  analysis  and  5%  of  combustible. 


EVAPORATION   TESTS    OF  STEAM-BOOLE  RS. 


581 


Efficiency  of  boiler,  furnace,  and  grate,  based  on  coal  as  fired,  70%. 
The  gas  analysis  shows  that  20  Ib.  of  air  is  supplied  per  Ib.  of  C 

burned;  and  that  0.05  Ib,  of  C  was  burned  to  CO,  per  Ib.  of  carbon 

burned. 
The  air  is  supplied  at  92°  F.,  and  contains  0.02  Ib.  of  water  vapor 

per  Ib.  of  dry  air  (60%  relative  humidity).     Flue  gas  temperature 

592°  F. 
Water  from  and  at  212°  per  Ib.  coal  as  fired  10.258;  dry  coal  10.467; 

combustible  12.068. 


B.T.U.  per  Lb. 

Combustible. 

Coal  as 
Fired. 

Dry  Coal. 

Percent. 

B.T.U. 

Percent. 

a.  Heat  absorbed  by  the  boiler 
(Item  39,  40  or  41  X  970.4) 
6.  Loss  due  to  evaporation  of 
moisture  in  coal,  0.02  X  (212 
-92)+970  +  .47(592-212) 
c.  Loss  due  to  heat  carried  away 
by   steam   formed   by   the 
burning  of  hydrogen  0.04  X 
9  X  (120X970  +0.47X380). 
d.  Loss  due  to  heat  carried  away 
in  the  dry  flue  gases,  21  Ib. 
per  Ib.  €  =  21X0.77  =  16.17 
X  500X0.24 

9954 
25 

457 

1940 

391 
790 

72 
591 
14,220 

10157 
26 

466 

1979 

399 
806 

74 
603 
14,510 

70 
0.2 

3.2 

13.7 

2.7 
5.6 

0.5 
4.1 
100.00 

11711 

29 

538 

2282 
460 

86 
694 
15,800 

74.1 

0.2 
3.4 

14.4 
2.9 

0.5 
4.5 
100.0 

e.  Loss  due  to  carbon  monoxide 
0.05X0.77  =  .0385  C  per  Ib. 
coal  X  10,  150.  .. 

/.   Loss  due  to  combustible  in 
ash  and  refuse,  0.05  X  15800 
g.  Loss  due  to  heating  moisture 
in  air,  0.02X20X0.77X500 
X0.47 

h.  Loss  due  to  unconsumed  hy- 
drogen and  hydrocarbons, 
to    radiation,     and    unac- 
counted for   .  . 

i.   Total  calorific  value  of  1  Ib.  of 
coal,  as  fired,  dry  coal,  or 
combustible  (Lines  42  and 
43  and  footnote)  

If  the  fuel  lost  in  ash  and  refuse  is  not  the  combustible  of  the  original  coal, 
but  coke  or  carbon  of  a  heating  value  of  14,600  B.T.U.  per  Ib.,  then  the  heat 
loss  due  to  it  is  0.05X14,600  =  730  instead  of  790  B.T.U.  The  heating  value 
per  Ib.  of  combustible  burned  would  then  be  (14,220 -730) -=-0.85  =  15,870 
instead  of  15,800.  The  percentage  figures  in  the  last  column  would  be  changed 
accordingly,  and  the  efficiency  of  the  boiler  and  furnace  would  be  (1 1,711  -f- 
15,870)  =73.78%  instead  of  74.1%. 

In  this  table  the  calculations  expressed  in  the  text  (excepting  Item  a)  refer 
to  the  quantities  given  in  the  first  column,  which  are  based  on  coal  as  fired. 
The  quantities  in  the  second  column,  which  are  based  on  dry  coal,  are  obtained 
from  those  in  the  first  column  by  dividing  each  one  by 


582  STEAM-BOILER  ECONOMY. 

The  items  are  designated  the  same  as  those  given  in  the  tabular  form  of  the 
report  under  Item  55. 


Until  recently  two  methods  of  determining  moisture  in  coal  have  been  in 
common  use:  first,  the  one  usually  adopted  in  boiler-testing,  which  consists 
in  drying  a  large  sample,  fifty  pounds  or  more,  in  a  shallow  pan  placed  over 
the  boiler  or  flue;  second,  the  method  usually  followed  by  chemists,  of  drying 
a  one-gram  sample  of  pulverized  coal  at  212°  F.,  or  a  little  above,  for  an  hour, 
or  until  constant  weight  is  obtained.  Both  methods  are  liable  to  large  errors. 
In  the  first  method,  the  temperature  at  which  the  drying  takes  place  is  un- 
certain, and  there  is  no  means  of  knowing  whether  the  temperature  obtained  is 
sufficient  to  drive  off  the  moisture  that  is  held  by  capillary  force  or  other 
attraction  within  the  lumps  of  coal,  which,  at  least  in  case  of  bituminous  coals 
seems  to  be  as  porous  as  wood,  and  as  capable  of  absorbing  moisture  from  the 
atmosphere.  The  second  method  is  liable  to  greater  errors  in  sampling  than  the 
first,  and  during  the  process  of  fine  crushing  and  passing  through  sieves,  a 
considerable  portion  of  the  moisture  is  apt  to  be  removed  by  air-drying.  In 
an  extensive  series  of  boiler-tests  made  by  the  writer  in  the  summer  of  1896, 
it  became  necessary  to  find  more  accurate  means  of  determining  moisture  than 
either  of  those  above  described.  It  was  found  by  repeated  heating  at  grad- 
ually increasing  temperatures  from  212°  up  to  300°  or  over,  and  weighing  at 
intervals  of  an  hour  or  more,  that  the  weight  of  coal  continually  decreased 
until  it  became  nearly  constant,  and  then  a  very  slight  increase  took  place, 
which  increase  became  greater  on  further  repeated  heatings  to  temperatures  above 
250°.  It  has  often  been  stated  that  if  coal  is  heated  above  212°  F.,  volatile 
matter  will  be  driven  off;  but  repeated  tests  on  seventeen  different  varieties 
of  coal  mined  in  western  Pennsylvania,  Ohio,  Indiana,  Illinois  and  Kentucky 
invariably  showed  a  gradual  decrease  of  weight  to  a  minimum,  followed  by  the 
increase,  as  stated  above,  and  in  no  single  case  was  there  any  perceptible  odor 
or  other  indication  of  volatile  matter  passing  off  below  a  temperature  of  350 °' 
The  fact  that  no  volatile  matter  was  given  off  was  further  proved  by  heating 
the  coal  in  a  glass  retort  and  catching  the  vapor  driven  off  in  a  bottle  filled 
with  water  and  inverted  in  a  basin;  the  air  displaced  from  the  retort  by  expan- 
sion due  to  the  heating  displacing  the  water  in  the  bottle.  When  the  retort 
was  cooled,  after  being  heated  to  350°  in  an  oil  bath,  the  air  thus  expanded 
contracted,  and  returned  from  the  bottle  to  the  retort,  leaving  the  bottle  full 
of  water,  as  at  the  beginning  of  the  heating,  showing  that  no  gas  had  been  given 
off,  except  possibly  such  exceedingly  small  amount  as  might  be  absorbed  by 
he  water.  The  method  described  in  Section  XV  of  the  report  f  was  then, 
adopted  as  the  best  available  method  of  determining  the  moisture  in  these  coals. 
Its  accuracy  was  further  checked  by  other  methods.  J 

The  new  method  of  drying  and  its  results  were  communicated  by  the  writer 
to  Prof.  R.  C.  Carpenter  of  Cornell  University,  shortly  after  they  were  made, 
and  he  thereupon  began  experimenting  with  the  method,  and  fully  confirmed 
the  writer's  conclusions.  In  a  letter  dated  May  18,  1897,  he  says:  "  We  have 
investigated  the  moisture  question,  and  find  that  in  all  the  samples  tested,  some 
four  or  five  in  number,  there  is  no  appreciable  loss  between  temperatures  250 
and  350  degrees;  at  least  the  loss  is  less  than  our  means  of  weighing."  In  his 
paper  on  "  Hygrometric  Properties  of  Coals,"  presented  at  the  Hartford, 
meeting  (Transactions,  vol.  xviii.  p.  948),  he  says: 


*  This  and  following  articles  are  from  the  signed  appendices  to  the  Code  of  1899,  some- 
what abridged.  The  initials  are  those  of  Geo.  H.  Barrus,  J.  C.  Hoadley,  and  the  author. 

t  The  same  method  is  recommended  in  the  Report  of  the  Power  Test  Committee  in  1915. 

i  For  scientific  investigations  in  which  extreme  accuracy  is  desired,  the  author  would 
suggest  that  the  coal  be  dried  in  an  atmosphere  of  nitrogen,  to  avoid  oxidation,  and  that  the 
moisture  driven  off  be  absorbed  by  chloride  of  calcium  and  weighed.  The  loss  of  weight 
by  the  coal  should  equal  the  gain  of  weight  by  the  chloride  of  calcium  if  no  volatile  matter 
is  driven  off. 


EVAPORATION   TEXTS  OF  STEAM-BOILERS.  583 

"  With  the  most  volatile  coals,  there  is  no  sensible  loss  of  weight  due  to 
driving  off  the  volatile  matter  under  a  temperature  of  380°  Fahr.,  and  with 
an  anthracite  coal  there  is  no  sensible  loss  under  a  temperature  of  700°  Fahr." 

w.  K. 


DETERMINATION    OF    THE    MOISTURE    IN   THE    STEAM. 

The  throttling  steam  calorimeter,*  first  described  by  Professor  Peabody 
in  Trans.  A.S.M.E.,  vol.  x.  page  327,  and  its  modifications  by  Mr.  Barrus 
vol.  xi.  page  790;  vol.  xvii.  page  617;  and  by  Professor  Carpenter,  vol.  xii. 
page  840;  also  the  separating  calorimeter  designed  by  Professor  Carpenter, 
vol.  xvii.  page  608;  which  instruments  are  used  to  determine  the  moisture 
existing  in  a  small  sample  of  steam  taken  from  the  steam-pipe,  give  results, 
when  jroperly  handled,  which  may  be  accepted  as  accurate  within  0.5  per 
cent  (this  percentage  being  computed  on  the  total  quantity  of  the  steam)  for  the 
sample  taken.  The  possible  error  of  0.5  per  cent  is  the  aggregate  of  the  prob- 
able error  of  careful  observation,  and  of  the  errors  due  to  inaccuracy  of  the  pres- 
sure-gauges and  thermometers,  to  radiation,  and,  in  the  case  of  the  throttling- 
calorimeter,  to  the  possible  inaccuracy  of  the  figure  0.46  for  the  specific  heat 
of  superheated  steam,  which  is  used  in  computing  the  results.  It  is,  however, 
by  no  means  certain  that  the  sample  represents  the  average  quality  of  the 
steam  in  the  pipe  from  which  the  sample  is  taken.  The  practical  impossibility 
of  obtaining  an  accurate  sample,  especially  when  the  percentage  of  moisture 
exceeds  two  or  three  per  cent,  is  shown  in  the  two  papers  by  Professor  Jacobus 
in  Transactions,  vol.  xvi.  pages  448,  1017. 

In  trials  of  the  ordinary  forms  of  horizontal  shell  and  of  watertube  boilers, 
in  which  there  is  a  large  disengaging  surface,  when  the  water-level  is  carried 
at  least  10  inches  below  the  level  of  the  steam  outlet,  and  when  the  water  is 
not  of  a  character  to  cause  foaming,  and  when  in  the  case  of  water-tube  boilers 
the  steam  outlet  is  placed  in  the  rear  of  the  middle  of  the  length  of  the  water- 
drum,  the  maximum  quantity  of  moisture  in  the  steam  rarely,  if  ever,  exceeds 
two  per  cent;  and  in  such  cases  a  sample  taken  with  the  precautions  specified 
in  the  Code  may  be  considered  to  be  an  accurate  average  sample  of  the  steam 
furnished  by  the  boiler,  and  its  percentage  of  moisture  as  determined  by  the 
throttling  or  separating  calorimeter  may  be  considered  as  accurate  within 
one-half  of  one '  per  cent.  For  scientific  research,  and-  in  all  cases  in  which 
there  is  reason  to  suspect  that  the  moisture  may  exceed  two  per  cent,  a  steam 
separator  should  be  placed  in  the  steam-pipe,  as  near  to  the  steam  outlet  of  the 
boiler  as  convenient,  well  covered  with  felting,  all  the  steam  made  by  the 
boiler  passing  through  it,  and  all  the  moisture  caught  by  it  carefully  weighed 
after  being  cooled.  A  convenient  method  of  obtaining  the  weight  of  the  drip 
from  the  separator  is  to  discharge  it  through  a  trip  into  a  barrel  of  cold  water 
standing  on  a  platform  scale.  A  throttling  or  a  separating  calorimeter  should 
be  placed  in  the  steam-pipe,  just  beyond  the  steam  separator,  for  the  purpose 
of  determining,  by  the  sampling  method,  the  small  percentage  of  moisture  which 
may  still  be  in  the  steam  after  passing  through  the  separator. 


*The  throttling  calorimeter  is  based  on  the  fact  that  steam  containing  a  small  percentage 
of  moisture  is  dried  by  throttling  and  superheated  to  a  temperature  above  that  due  to  its 
reduced  pressure.  It  consists  essentially  of  i-in.  pipe  fittings  containing  a  flange  coupling 
in  which  is  inserted  a  thin  blank  flange  or  disk  perforated  with  a  hole  5  in.  or  less  in  diameter. 
The  steam  from  the  sampling  pipe  passes  through  this  hole  into  a  small  exhaust  chamber 
fitted  with  a  mercury  well  and  thermometer.  The  difference  between  the  temperature  of  the 
throttled  steam,  as  shown  by  this  thermometer  and  that  due  to  its  pressure  (subject  to  a 
slight  correction  for  radiation)  is  the  superheating,  and  from  this  the  moisture  is  calculated 
by  a  formula  which  is  based  on  the  principle  that  the  total  heat  of  the  moist  steam  before 
throttling  is  the  same  as  that  of  the  dry  steam  after  throttling  if  there  is  no  loss  or  gain  of 
heat  by  radiation  or  conduction.  To  lessen  the  transfer  of  heat  by  conduction,  asbestos  washers 
should  be  placed  on  each  side  of  the  disk,  and  to  lessen  radiation  the  whole  instrument  should 
be  enclosed  in  a  non-conducting  covering. 


584  STEAM-BOILER  ECONOMY. 

The  formula  for  calculating  the  percentage  of  moisture  when  the  throttling 
calorimeter  is  used  is  the  following: 


in  which  w  =  percentage  of  moisture  in  the  steam,  H  =  total  heat,  and  L  =  latent 
heat  per  pound  of  steam  at  the  pressure  in  the  steampipe,  h  =  total  heat  per 
pound  of  steam  at  the  pressure  in  the  discharge  side  of  the  calorimeter,  k  =  specific 
heat  of  superheated  steam,  T  =  temperature  of  the  throttle  and  superheated 
steam  in  the  calorimeter,  and  t  =  temperature  due  to  the  pressure  in  the  dis- 
charge side  of  the  calorimeter,  =212°  Fahr.,  at  atmospheric  pressure.  Taking 
fc  =  0.46  and  £  =  212,  the  formula  reduces  to 


W.    K. 
CORRECTION    FOR    RADIATION    FROM    THROTTLING    CALORIMETERS. 

The  formulae  usually  given  for  determining  moisture  in  a  throttling  calorim- 
eter makes  no  allowance  for  radiation  from  the  exterior  surfaces  of  the  instrument. 
It  is  true  that  this  allowance  is  small  and  does  not  affect  the  results  but  a  small 
fraction  of  1  per  cent;  but  it  nevertheless  exists,  and  should  properly  be  taken 
into  account.  In  my  own  work  I  have  found  that  the  radiation  reduces  the 
temperature  of  the  wire-drawn  steam  some  six  degrees,  and  this  represents 
about  0.3  of  1  per  cent  of  moisture.  My  practice  is  to  allow  for  the  radiation 
by  determining  the  normal  temperature  for  the  instrument  by  obtaining  a 
reading  of  the  thermometer  when  the  fires  are  in  a  dead  condition  and  the  super- 
heat has  disappeared;  this  temperature  being  observed  when  the  pressure  as 
shown  by  the  gauge  is  the  average  of  the  readings  taken  during  the  trial. 
Observations  being  made  by  the  same  instrument,  errors  of  gauge  or  ther- 
mometer are  practically  eliminated. 

G.  H.  B. 

"  NORMAL  READING  "  OF  A  CALORIMETER.* 

To  determine  the  "  normal  "  reading  of  the  low-pressure  thermometer  cor- 
responding to  dry  steam,  the  instrument  should  be  attached  to  a  horizontal 
steam  pipe  in  such  a  way  that  the  sampling  nozzle  projects  upwards  to  near 
the  top  of  the  pipe,  there  being  no  perforations  and  the  steam  entering  through 
the  open  top  of  the  nozzle.  The  test  should  be  made  when  the  steam  in  the 
pipe  is  in  a  quiescent  state,  and  when  the  steam  pressure  is  maintained  con- 
stantly at  the  point  observed  on  the  main  trial.  If  the  steam  pressure  falls 
during  the  time  when  the  observations  are  being  made,  the  test  should  be 
continued  long  enough  to  obtain  the  effect  of  an  equivalent  rise  of  pressure. 

To  find  the  "  constant  "  for  1  per  cent  of  moisture,  divide  the  latent  heat 
of  the  steam  supplied  to  the  calorimeter  at  the  observed  pressure  or  tempera- 
ture by  the  specific  heat  of  superheated  steam  at  atmospheric  pressure  (0.46) 
and  divide  the  quotient  by  100. 

Finally  ascertain  the  percentage  of  moisture  by  dividing  the  number  of 
degrees  of  cooling  by  the  constant,  as  above  noted. 

To  determine  the  quantity  of  steam  used  by  the  calorimeter  it  is  usually 
sufficient  to  calculate  the  quantity  from  the  area  of  the  orifice  rnd  the  abso- 
lute pressure,  using  Napier's  formula  for  the  number  of  pounds  passing 
through  per  second;  that  is,  absolute  pressure  in  Ib.  per  sq.  in  divided  by 
70  and  multiplied  by  the  area  of  orifice  in  sq.  in.  To  determine  the  quantity 

*  From  Appendix  to  Code  of  1915. 


EVAPORATION   TESTS  OF  STEAM-BOILERS. 


585 


by  actual  test,  a  steam  hose  may  be  attached  to  the  outlet  of  the  calorimeter 
and  carried  to  a  barrel  of  water  on  platform  scales.  The  amount  of  steam 
condensed  in  a  certain  time  is  determined  and  thereby  the  quantity  discharged 
per  hour. 

COMBINED  CALORIMETER  AND  SEPARATOR. 

A  form  of  steam  calorimeter  which  the  writer  uses  is  termed  the  "  1895 
pattern  "  universal  steam  calorimeter,  and  is  a  modification  of  the  one  described 
in  the  Transactions,  vol.  xi.  p. 
790.  It  is  illustrated  in  the 
accompanying  cut,  Fig.  248, 
which  is  reprinted  from  p.  618, 
vol.  xvii  in  the  Transactions. 
It  consists  of  a  throttling  calo- 
rimeter and  separator  combined, 
the  latter  being  attached  to  the 
outlet  where  the  steam  of  at- 
mospheric pressure  is  escaping. 
If  the  moisture  is  too  great  to 
be  determined  by  the  readings 
of  the  two  thermometers,  the 
separator  catches  the  balance, 
and  the  total  quantity  of  mois- 
ture is  made  up  in  part  of  that 
shown  by  the  thermometers, 
and  in  part  of  that  collected 
from  the  separator. 

G.  H.  B. 

EFFICIENCY  OF  THE  BOILER. 

FIG.  248. — STEAM  CALORIMETER. 

The  efficiency  of  the  boiler, 
not   including  the  grate  (or  the 

efficiency  based  upon  combustible)  is  a  more  accurate  measure  of  comparison  of 
different  boilers  than  the  efficiency  including  the  grate  (or  the  efficiency  based 
upon  coal);  for  the  latter  is  subject  to  a  number  of  variable  conditions,  such 
as  size  and  character  of  the  coal,  air-spaces  between  the  grate-bars,  skill  of 
the  fireman  in  saving  coal  from  falling  through  the  grate,  etc.  It  is,  moreover, 
subject  to  errors  of  sampling  the  coal  for  drying  and  for  analysis,  which  affect  the 
result  to  a  greater  degree  than  they  do  the  efficiency  based  upon  combustible, 
for  the  reason  that  the  heating  value  per  pound  of  combustible  of  any  sample 
selected  from  a  given  lot,  such  as  a  car-load,  of  coal  is  practically  a  constant 
quantity  and  is  independent  of  the  percentage  of  moisture  and  ash  in  the  sample; 
while  the  sample  itself,  upon  the  heating  value  of  which  the  efficiency  based  on 
coal  is  calculated,  may  differ  in  its  percentage  of  moisture  and  ash  from  the 
average  coal  used  in  the  boiler-test. 

When  the  object  of  a  boiler-test  is  to  determine  its  efficiency  as  an  absorber 
of  heat,  or  to  compare  it  with  other  boilers,  the  efficiency  based  on  combustible 
is  the  one  which  should  be  used;  but  when  the  object  of  the  test  is  to  deter- 
mine the  efficiency  of  the  combination  of  the  boiler,  the  furnace,  and  the  grate, 
the  efficiency  based  on  coal  must  necessarily  be  used. 

W.    K. 
DRAFT-GAUGE. 

The  ordinary  form  of  draft-gauge,  consisting  of  the  U  tube  (Fig.  249), 
containing  water,  lacks  sensitiveness  when  used  for  measuring  small  quanti- 
ties of  draft.  An  instrument  which  the  writer  has  used  satisfactorily  for  a 
number  of  years  multiplies  the  ordinary  indications  as  many  times  as  desired, 


586 


STEAM-BOILER  ECONOMY. 


It  consists  of  a  IT  tube  made  of  £-m.  glass,  surmounted  by  two  larger  tubes; 
or  chambers,  having  a  diameter  of  1\  ins.,  as  shown  in  Fig.  250.  Two  different 
liquids  which  will  not  mix,  and  which  are  of  different  color,  are  used,  one  occupy- 
ing the  portion  AB,  and  the  other  the  portion  BCD.  The  movement  of  the 
line  of  demarcation  is  proportional  to  the  difference  in  the  areas  of  the  chambers 
and  of  the  U  tube  below.  The  liquids  generally  employed  are  alcohol  colored 
red  and  a  certain  grade  of  lubricating  oil.  A  multiplication  varying  from  eight 


FIG.  249. 


U-TUBE  DRAFT-GAUGE, 
HALF  SIZE. 


FIG.  250. — BARRUS'S  DRAFT-GAUGE, 
WITH  MAGNIFIED  READINGS. 


to  ten  times  is  obtained  under  these  circumstances;    in  other  words,  with  i-in, 
draft  the  movement  of  the  line  of  demarcation  is  some  2  ins. 

The  instrument  is  calibrated  by  referring  it  to  the  ordinary  U-tube  gauge. 

G.  H.  B. 

DRAFT-GAUGE. 

The  accompanying  sketch  (Fig.  251)  represents  a  very  sensitive  and  accu- 
rate draft-gauge  recently  constructed  by  the  writer.  A  light  cylindrical  tin 
can  A,  5  ins.  diameter  and  6  ins.  high,  is  inverted  and  suspended  inside  of  a 
can  B,  6  ins.  diameter,  6  ins.  high,  by  means  of  a  long  helical  spring.  Inside 
of  the  larger  can  a  j-in.  tube  is  placed,  with  one  end  just  below  the  level  of  the 
upper  edge,  while  the  other  end  passes  through  a  hole  cut  in  the  side  of  the  can, 
close  to  the  bottom,  solder  being  run  around  the  tube  so  as  to  close  the  hole 
and  make  the  can  water-tight.  The  can  is  filled  with  water  to  within  about 
half  an  inch  of  the  top.  and  the  inner  can  is  suspended  by  the  spring  so  that 
its  lower  edge  dips  into  the  water,  the  height  of  the  support  of  the  spring  being 
adjusted  accordingly. 

The  small  tube  being  open  at  both  ends,  the  air  enclosed  in  the  can  A  is  at 
atmospheric  pressure,  and  the  spring  is  extended  by  the  weight  of  the  can 


EVAPORATION   TESTS  OF  STEAM-BOILERS. 


587 


The  end  of  the  tube  which  projects  from  the  bottom  of  the  can  being  now  con- 
nected by  means  of  a  rubber  tube  with  a  tube  leading  into  the  flue,  or  other 
chamber  whose  draft  or  suction  is  to  be  measured, 
air  is  drawn  out  of  the  can  A  until  the  pressure  of 
the  remaining  air  is  the  same  as  that  of  the  flue. 
The  external  atmosphere  pressing  on  the  top  of  the 
can  A  causes  it  to  sink  deeper  in  the  water,  extend- 
ing the  spring  until  its  increased  tension  just 
balances  the  difference  of  the  opposing  vertical 
pressures  of  the  ah-  inside  and  outside  of  the  can. 
The  product  of  this  difference  in  pressure,  expressed 
as  a  decimal  fraction  of  a  pound  per  square  inch, 
multiplied  by  the  internal  area  of  the  can  in 
square  inches,  equals  the  tension  of  the  spring 
(above  that  due  to  the  weight  of  the  can)  in 
pounds  or  fraction  of  a  pound.  The  extension  of 
a  helical  spring  being  proportional  to  the  force 
applied,  the  distance  travelled  downward  by  the 
can  A  measures  the  force  of  suction,  that  is,  the 
draft.  The  movement  of  the  can  may  conveniently 
be  measured  by  having  a  celluloid  scale  grad- 
uated to  50ths  of  an  inch  fastened  to  the  side  of 
the  can  A,  and  a  fine  pointer  fixed  to  the  upper 
edge  of  the  can  B,  almost  touching  the  scale. 

To  reduce  the  readings  of  the  scale  to  their 
equivalents  in  inches  of  water-column,  as  read  on 
the  ordinary  U-tube  gauge;  we  have  the  following 
formulae:  _  FlG  251.— DRAFT-GAUGE 

Let  P=force  in  pounds  required  to  stretch  the      FOR  LIGHT  PRESSURES. 

spring  1  in.; 

E  =  elongation  of  the  spring  in  inches; 
A  =area  of  the  inner  can  in  square  inches; 

d  =  difference  in  pressure  or  force  of  the  draft  in  pounds  per  square  inch; 
D= difference  in  pressure  in  inches  of  water = 27. 7ld. 


EP 


27.71 


E 


A 
Q.Q3Q1AD 


The  last  equation  shows  that  for  a  constant  force  of  draft  the  elongation 
of  the  spring  or  the  movement  of  the  can  may  be  increased  by  increasing  the 
area  of  the  can  or  by  decreasing  the  strength  of  the  spring.  The  strength  of 
the  spring  may  be  increased,  that  is,  its  sensitiveness  may  be  decreased,  by 
increasing  either  its  length  or  the  diameter  of  the  helix,  or  by  decreasing  the 
diameter  of  the  wire  of  which  it  is  made.  We  thus  have  at  command  the  means 
of  making  the  apparatus  of  any  desired  degree  of  sensitiveness. 

Applying  the  above  formulae,  let  it  be  required  to  determine  the  move- 
ment of  the  can  corresponding  to  a  draft  of  1  in.  of  water-column,  the  can  A 
having  a  diameter  of  5  ins.  =  19.63  ins.  area,  and -the  spring  of  such  a  strength 
that  0.1  Ib.  elongates  it  1  in.  Here  P  =  0.1;  A  =  19.63;  D  =  l. 


0.0361X19.63 
0.1 


=  7.09  inches. 


588 


STEAM-BOILER  ECONOMY. 


That  is,  the 
The  precision  of 
indicate;  for  in 
the  difference  in 
in  the  scale  may 
is  equivalent  to 
be  calibrated  by 
tube  gauge. 


instrument  multiplies  the  readings  of  the  U  tube  7.09  times, 
the  instrument  is,  however,  far  greater  than  this  figure  would 
the  U  tube  it  is  exceedingly  difficult  to  read  with  precision 
height  of  the  two  menisci,  while  with  this  apparatus  readings 
easily  be  made  to  5*0  in.,  which,  with  the  multiplication  of  7, 
sio  of  an  inch  of  water-column.  The  instrument  may  also 
directly  comparing  its  readings  with  those  of  an  ordinary  U- 


w.  K. 


SAMPLING    FLUE -GASES. 


Very  great  diversities  in  the  composition  of  flue-gases  often  exist  in  the 

same  flue  at  the  same  time.  To 
obtain  a  fair  sample,  it  has  been 
found  sufficient  to  have  one  orifice 
to  draw  off  gases  through  for  each 
25  sq.  ins.  of  cross-section  of  flue. 
The  pipes  must  be  of  equal 
diameter  and  of  equal  length. 
One-quart er-in.  gas-pipes,  all  alike 
at  the  ends,  and  of  equal  lengths, 
answer  well.  Similar  steel  tubes 
will  be  still  better  (because 
smoother  and  more  uniform). 
These  should  be  secured  in  a 
box  or  block  of  galvanized  sheet 
iron,  equal  in  thickness  to  one 
course  of  brick,  in  such  a  manner 
that  the  open  ends  may  be  evenly 
distributed  over  the  area  of  the 
flue  A  (Fig.  252),  and  their  other 
open  enclosed  in  the  receiver  B. 
If  the  flue-gases  be  drawn  off 
from  the  receiver  B  by  four 
tubes,  CC,  into  a  mixing-box  D 
beneath,  about  3-in.  cube,  a  good 
mixture  can  be  obtained.  Two 
such  "  samplers,"  one  above  the 
other  a  foot  apart,  in  the  same 
flue,  will  furnish  samples  of  gases 
which  show  by  analysis  the  same  composition. 

j.  c.  H. 
THE    RINGELMANN    SMOKE -CHART. 

Professor  Ringelmann,  of  Paris,  has  invented  a  system  of  determining  the 
relative  density  or  blackness  of  smoke.  In  making  observations  of  the  smoke 
proceeding  from  a  chimney,  four  cards  ruled  like  those  in  the  cut  (Fig.  253), 
together  with  a  card  printed  in  solid  black  and  another  left  entirely  white, 
are  placed  in  a  horizontal  row  and  hung  at  a  point  about  50  ft.  from  the  observer 
and  as  nearly  as  convenient  in  line  with  the  chimney.  At  this  distance  the  lines 
become  invisible,  and  the  cards  appear  to  be  of  different  shades  of  gray,  rang- 
ing from  very  light  gray  to  almost  black.  The  observer  glances  from  the  smoke 
coming  from  the  chimney  to  the  cards,  which  are  numbered  from  0  to  5,  deter- 
mines which  card  most  nearly  corresponds  with  the  color  of  the  smoke  and 
makes  a  record  accordingly,  noting  the  time.  Observations  should  be  made 
continuously  during  say  one  minute,  and  the  estimated  average  density  dur- 
ing that  minute  recorded,  and  so  on,  records  being  made  once  every  minute. 
The  average  of  all  the  records  made  during  a  boiler-test  is  taken  as  the  average 
figure  for  the  smoke  density  during  the  test,  and  the  whole  of  the  record  is 
plotted  on  cross-section  paper  in  order  to  show  how  the  smoke  varied  in  density 


FIG.  252. — METHOD  OF  SAMPLING  FLUE- 
GASES. 


EVAPORATION   TESTS  OF  STEAM-BOILERS. 


589 


No.  1. 


No.  2. 


No.  3.  No.  4. 

FIG.  253. — THE  RINGELMANN  SCALE  FOR  GRADING  THE  DENSITY  OF  SMOKE. 


590  STEAM-BOILER  ECONOMY. 

from  time  to  time.    A  rule  by  which  the  cards  may  be  reproduced  is  given 
by  Professor  Ringlemann  as  follows: 

Card  0— All  white. 

Card  1 — Black  lines  .1  mm.  thick,  10  mm.  apart,  leaving  spaces  9  mm. 
square. 

Card  2 — Lines  2.3  mm.  thick,  spaces  7.7  mm  square. 

Card  3 — Lines  3.7  mm.  thick,  spaces  6.3  mm.  square. 

Card  4 — Lines  5.5  mm.  thick,  spaces  4.5  mm.  square. 

Card  5— All  black. 

The  cards  as  printed  on  the  opposite  page  are  much  smaller  than  those 
used  by  Professor  Ringelmann.  The  thickness  and  spacing  of  the  lines  are 
in  the  same  proportion,  but  reduced  to  one-half  size. 

w.  K. 

STARTING   AND    STOPPING   A   TEST. 

A  special  caution  is  needed  against  a  modification  of  the  "  alternate " 
method,*  which  has  been  adopted  by  some  testing  engineers  within  the  past 
few  years.  It  consists  in  taking  the  starting  and  the  stopping  times  each  at  a 
time  subsequent  to  the  cleaning,  say  after  400  Ibs.  of  coal  has  been  fired  since 
the  cleaning.  There  are  two  sources  of  serious  error  in  this  method,  one  caus- 
ing an  incorrect  measurement  of  the  coal,  the  other  an  incorrect  measurement 
of  the  water.  Suppose  200  Ibs.  of  hot  coke  are  left  on  the  grate  at  the  end 
of  cleaning  and  400  Ibs.  of  fresh  coal  are  added  by  the  end  of,  say,  half  an  hour 
after  cleaning.  If  the  coal  left  at  the  end  of  the  cleaning,  and  the  boiler-walls 
also,  are  very  hot,  and  the  coal  is  highly  volatile  and  dry  and  the  pieces  of 
such  size  as  not  to  choke  the  air-supply,  the  fire  may  burn  so  briskly  that  at 
the  end  of  the  half-hour  the  fuel-value  of  the  partly-burned  coal  left  out  of  the 
total  600  Ibs.  is  equivalent  only  to  200  Ibs.  of  coal.  If,  on  the  contrary,  the  hot 
coke  on  the  grates  at  the  end  of  the  cleaning,  and  the  boiler-walls,  are  con- 
siderably cooled,  if  the  fresh  coal  fired  is  moist  and  of  small  size,  such  as  the 
slack  of  run-of-mine  bituminous  coal,  which  is  often  found  in  one  portion  of  a 
pile  in  greater  quantity  than  in  another,  the  fire  during  the  half-hour  may  burn 
so  sluggishly  that  the  coal  and  coke  on  the  grate  at  the  end  of  the  half-hour 
may  have  a  fuel-value  equal  to  400  Ibs.  of  coal.  If,  in  this  case,  it  is  assumed 
that  the  quantity  and  condition  of  the  coal  at  the  end  of  the  half-hour  after 
cleaning  are  the  same  at  the  starting  and  stopping  time;  and,  if  the  fire  burned 
briskly  during  the  half-hour  before  starting  and  slowly  duiing  the  half-hour 
before  stopping,  the  boiler  will  be  charged  with  more  coal  than  was  actually 
burned.  If,  on  the  contrary,  the  coal  burns  away  more  slowly  during  the  half- 
hour  after  the  cleaning  before  the  starting  time  and  more  rapidly  during  the  half- 
hour  before  the  end  of  the  test,  the  boiler  is  not  charged  with  as  much  coal  as 
was  actually  burned. 

The  error  in  water-measurement  is  due  to  the  fact  that  the  condition  of 
the  fire,  and  especially  the  quantity  of  flaming  gases  arising  from  it,  influences 
the  height  of  the  water-level.  A  bright  hot  fire,  or  a  fire  with  an  abundance 
of  burning  gas  proceeding  from  it,  causes  the  water-level  to  rise;  while  any- 
thing that  cools  the  furnace,  such  as  freshly-fired  coal,  an  open  fire-door,  or  a 
check  to  the  draft,  causes  the  water-level  to  fall.  A  rise  or  a  fall  of  several 
inches  in  a  few  seconds  frequently  occurs  when  bituminous  coal  is  used.  If 
the  water-level  is  noted  at  the  starting  of  the  test,  when  it  is  raised  by  a  bright 
fire,  and  at  the  end  of  a  test,  when  it  is  depressed  by  the  stoppage  of  violent 
ebullition  or  of  rapid  circulation,  due  to  the  cooling  of  the  fire,  the  boiler  will 
be  credited  with  more  water  than  was  really  evaporated,  and  vice  versa % 

The  only  correct  times  to  be  noted  as  the  starting  and  the  stopping  times 
are  when  the  smallest  amount  of  fuel  is  on  the  grate  and  when  it  is  in  the  most 
burned-out  condition;  that  is,  just  before  firing  fresh  coal  after  cleaning,  and 

*The  "  alternate"  method  of  the  Code  of  1899  is  the  standard  method  of  the  Code  of  1915. 
The  old  standard  method,  which  consisted  in  starting  with  a  wood  fire  and  stopping  by 
burning  down  and  withdrawing  all  ash  and  unburned  coal  from  the  grate,  is  now  abandoned. 


'EVAPORATION   TESTS  OF  STEAM-BOILERS.  591 

when  the  water-level  is  in  its  most  quiet  condition  and  the  least  raised  by  ebul- 
lition. The  furnace-door  has  then  been  kept  open  for  some  time  for  cleaning 
and  the  furnace  therefore  is  in  its  coolest  state.  This  condition  of  fire  and  of 
water-level  can  be  duplicated  immediately  after  cleaning  the  fire;  but  there  is 
no  certainty  of  duplication  of  any  condition  when  there  is  a  bright  fire  and 
consequent  rapid  steaming. 

These  statements  are  not  based  upon  theoretical  considerations,  but  are  the 
results  of  many  experiments  made  by  the  writer  to  determine  the  best  starting 
and  stopping  times.  In  a  long  series  of  tests  with  bituminous  coals  no  less  than 
six  different  times  were  recorded  as  starting  times  and  as  many  as  stopping 
times,  and  the  coal  apparently  used  and  the  water  apparently  evaporated  recorded 
and  calculated  for  each.  These  times  were:  A,  before  opening  the  first  or  right- 
hand  door  to  clean  the  fire;  B,  after  cleaning  the  first  half  of  the  furnace  and 
just  before  firing  fresh  coal;  C,  after  cleaning  the  second  half  of  the  furnace; 
D,  after  200  Ibs.  of  fresh  coal  had  been  fired;  E,  after  400  Ibs.;  F,  after  600  Ibs. 
By  plotting  the  apparent  water-evaporation  between  A  and  E,  both  for  starting 
and  for  stopping  times,  it  was  seen  that  there  was  nearly  always  an  apparent 
negative  evaporation  between  B  and  D,  and  sometimes  between  B  and  C  and 
between  B  and  E,  due  to  the  correction  for  height  of  observed  water-level,  the 
level  rising  rapidly,  being  much  greater  than  the  water  fed  by  the  pump.  There 
was  often  no  similarity  of  appearance  of  the  plotted  diagrams  between  A  and  F 
at  the  beginning  and  at  the  end  of  the  same  test.  The  possible  error  of  water- 
measurement  due  to  taking  A,  D,  E,  or  F  as  the  starting  time  was  sometimes 
as  much  as  2000  Ibs.  of  water,  or  about  3  per  cent  of  the  whole  amount  evapo- 
rated in  a  ten-hour  test.  The  record  of  water  evaporated  between  the  stop- 
ping and  starting  times  C  occasionally  differed  considerably  from  that  taken 
between  the  B  start  and  stop,  due  to  the  fact  that  sometimes  between  B  and  C 
there  was  a  sudden  lighting  up  of  the  fresh  coal  on  the  cleaned  side  of  the  fur- 
nace, while  at  other  times  the  fire  would  not  light  up  brightly  until  after  the  C 
point  had  passed.  It  was  therefore  decided  that  the  B  time,  when  the  furnace 
was  the  coldest  and  the  water-level  at  the  lowest,  was  the  only  time  which 
could  be  accepted  as  the  true  starting  and  stopping  time. 

w.  K. 

CHART   SHOWING   GRAPHICALLY  THE   LOG   OP   A  TRIAL. 

The  well-known  method  of  plotting  observations  and  data  on  cross-section 
paper,  and  making  a  chart  applying  to  the  test,  is  a  useful  means  of  represent- 
ing the  exact  uniformity  of  conditions  existing  during  a  trial.  Such  a  chart  is 
illustrated  in  the  appended  cut  (Fig.  257),  in  which  the  abscissae  represent 
times  and  the  ordinates  on  appropriate  scales  the  various  observations  and 
data. 

G.    H.    B. 

Computation  of  the  Results  of  a  Boiler  Trial. — The  following 
example  shows  a  convenient  method  of  making  the  calculations  of 
the  results  of  a  trial  from  the  observed  data  recorded  at  the  trial. 

The  observed  data  used  in  the  calculations  are: 

a.  Duration  of  the  test 10  hrs.  15  min.  =  10.25  hrs. 

6.  Water  apparently  evaporated Ibs.  30,000 

c.  Coal  used Ibs.  3,000 

d.  Feed-water  temperature,  average 110°  F. 

e.  Steam-pressure  by  gauge,  average Ibs.  120 

/.   Moisture  in  the  coal %  2 

g.  Moisture  in  the  steam %  0.5 

h.  Ash  and  refuse  withdrawn  from  the  fire 6%  =  Ibs.  180 

t.   Grate-surface sq.  ft.  30 

j.  Heating  surface sq.  ft.  1,000 


592 


STEAM-BOILER  ECONOMY. 


The  following  results  are  calculated  from  these  data: 
k.  Factor  of  evaporation,  from  d  and  e,  taken  from  table  of  factors,  1.15. 
bi  Water  evaporated,  corrected  for  moisture  in  the  steam  =  6— 06  =  30,000  — 150 

=  29,850  Ibs. 
U.E.  Water  evaporated  from  and  at  212°  into  dry  steam  =  biXk=  29,850 XI.  15 

=  34,327  Ibs. 

d  Dry  coal  =  c  -f  =  3000  -  60  =  2940  Ibs 
c2  Combustible  =  ci  -  h  =  2940  - 180  =  2760  Ibs. 


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P.M. 

FIG.  254. — GRAPHIC  RECORD  OF  A  BOILER  TEST. 


USEFUL  RESULTS. 

(1)  6-j-c  Water  apparently  evaporated  per  Ib.  coal,  actual  conditions  30, 000 -f- 

3000  =  10  Ibs. 

(2)  U.E.-i-c  Water  evaporated  from  and  at  212°  per  Ib.  coal,  34, 327 -r- 3000  = 

11.442  Ibs. 

(3)  U.E.-^-C!  Water  evaporated  from  and  at  212°  per  Ib.  dry  coal,  34327^-2940 

=  11.676  Ibs. 

(4)  U.E.-^-c>  Water  evaporated  from  and  at  212°  per  Ib.  combustible,  34,327 -f- 

2760  =  12.437  Ibs. 

(5)  H.P.  Horse-po wer  =  U.E.  -=- a  +  34.5  =  34,327  -f- 10.25 -7-34.5=  97.1  H.P. 

(6)  Coal  per  sq.  ft.  grate-surface  per  hour,  c -=- a -=-i  =  3000 ^10.25 ^30  =  9.76  Ibs. 

(7)  U.E    per  sq.   ft.  heating  surface  per  hour,   U.E.  ^ a  +j  =  34,327  4- 10.25  -f- 

1000  =  3.35  Ibs. 

(8)  T.  Temperature  of  the  chimney  gases,  average  450°  F. 

Interpretation  of  the  above  results. — The  results  given  in  the  last  eight  lines 
are  the  ones  that  give  practically  all  the  information  that  is  required  from  any 
boiler-trial.*  All  the  observed  data  and  all  the  computations  are  of  use  only 
for  the  purpose  of  obtaining  these  eight  results.  We  will  now  consider  what 
conclusions  may  be  drawn  by  an  engineer  from  these  eight  results  alone,  the 
figures  themselves  being  accepted  as  correct. 


*  That  is,  an  ordinary  trial  in  a  small  plant.      In  large  plants  the  results  here  given  should 
be  supplemented  by  coal  and  gas  analyses,  and  by  a  heat-balance  computed  from  them. 


EVAPORATION  TESTS  OF  STEAM-BOILERS.  593 

1.  From  the  result,  10  Ibs.  of  water  evaporated  under  actual  conditions 
nothing  can  be  known  concerning  the  efficiency  of  the  boiler  or  the  quality 
of  the  coal,  unless  the  conditions  of  feed-water  temperature,  steam-pressure, 
and  moisture  in  the  coal  and  in  the  steam  are  also  known.     About  the  only 
use  that  can  be  made  of  this  figure  is  in  connection  with  estimates  of  the  cost 
of  steam-power.     If  the  engine  using  the  steam  furnished  by  the  boiler  uses  20 
Ibs.  of  steam  per  horse-power  per  hour,  then  it  will  require  20  -=-10  =  2  Ibs.  of 
coal  per  horse-power,  the  "  actual  conditions  "  under  which  the  boiler  is  operated 
being  the  pressure  of  steam  required  by  the  engine  and  the  temperature  of  water 
in  the  hot-well  of  the  condenser  or  in  the  feed-water  heater,  both  of  which  obtain 
their  heat  from  the  exhaust  steam  furnished  by  the  engine. 

2.  The  result,  11.442  Ibs.  evaporated  from  and  at  212°  per  Ib.  of  coal,  is 
useful  as  a  measure  of  the  quality  of  the  coal,  provided  the  efficiency  of  the 
boiler  is  known.     For  tests  of  different  coals  with  the  same  boiler  and  under 
the  same  conditions  of  rate  of  driving,  kind  of  firing,  etc.,  this  figure  is  the  one 
that  will  be  used  in  comparing  the  relative  values  of  the  coals.     It  is  a  very  high 
figure,  and  indicates  both  that  the  coal  is  of  good  quality  and  that  the  efficiency 
of  the  boiler  is  high. 

3.  The  result,  11.676  U.E.  per  Ib.  of  dry  coal,  is  useful  in  connection  with 
result  2,  as  a  measure  of  the  quality  of  the  coal.     The  difference  between  the  two 
results  being  2%  shows  that  that  is  the  percentage  of  moisture  in  the  coal,  and 
this  would  indicate  that  the  coal  is  not  Western  coal.     The  result  would  also 
be  used  in  comparing  tests  of  coals  of  one  grade,  but  differing  in  surface-mois- 
ture, so  as  to  reduce  them  all  to  the  standard  of  dry  coal.     It  is  practically  of 
no  use  in  comparing  coals  of  different  grades,  such  as  Pittsburg  and  Illinois 
coals,  containing,,  respectively,  say  2%  and  12%  of  moisture. 

4.  The  result,  12.437  U.E.  per  Ib.  of  combustible,  is  the  one  used  for  com- 
paring boiler  efficiencies.     If  the  grade  of  coal  is  known,  and  its  heating  value 
per  Ib.  of  combustible  is  either  known  as  the  result  of  a  calorimetric  test  or  by 
computation  from  analysis,  or  estimated  from  the  average  heating  value  per 
Ib.  combustible  of  coal  of  that  grade,  then  the   figure  12.437  divided  by  the 
quotient  of  the  heating  value  of  the  coal  divided  by  965.7  will  give  the  efficiency. 
The  figure  12.437  being  in  excess  of  12  Ibs.,  which  is  practically  the  maximum 
value   obtainable  for  anthracite,   and  beyond   the  maximum   for  bituminous 
coal,  indicates  both  that  the  coal  is  semi-bituminous  and  that  the  boiler  was 
operated  with  a  very  high  efficiency.     Taking  the  average  heating  value  of  se^' 
bituminous  coal  at  15,750  B.T.U,  per  Ib.  combustible,  gives 

12.437        =76>26%  efficiency. 


15,750 -=-965.7 

5.  The  result,  97.1  H.P.,  is  the  measure  of  the  capacity  of  the  boiler  developed 
in  the  trial.     This  figure  will  be  compared  with  the  boiler's  rated  or  nominal 
capacity. 

6.  The  result,  9.76  Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour,  is  the  measure 
of  rate  of  driving  of  the  grate-surface.     It  is  a  rather  low  figure  for  semi- 
bituminous   coal   in   average  practice.     Taken   in   connection   with   the   high 
efficiency  it  indicates  exceptionally  good  firing,  very  nice  adjustment  of  the 
thickness  of  bed  of  coal  on  the  grate  to  the  force  of  the  draft,  and  an  excellent 
furnace,  a  combination  of  favorable  conditions  not  often  obtained. 

7.  The  rate  of  driving,  3.35  U.E.  per  sq.  ft.  of  heating  surface  per  hour, 
is  a  little  higher  than  that  at  which  maximum  economy  is  to  be  expected,  but, 
with  the  exceptionally  favorable  conditions  mentioned  in  the  preceding  para- 
graph, it  may  be  the  rate  corresponding  to  maximum  economy  in  this  case. 

8.  The  temperature  of  the  chimney-gases,  450°  F.,  is  unusually  low  for  semi- 
bituminous  coal  in  ordinary  practice.     It  indicates,  when  taken  in  connection 
with  the  high  efficiency,  which  is  inconsistent  with  air-leaks  in  the  setting,  a 
high  furnace  temperature  and  a  clean  boiler,  both  of  which  tend  to  produce  a 
low  chimney  temperature. 


594  STEAM-BOILER  ECONOMY. 

Erroneous  Conclusions  from  Competitive  Tests. — A  certain  water- 
tube  boiler  was  reported  to  have  shown  9.6%  saving  of  fuel  as  com- 
pared with  a  return-tubular  boiler  in  a  competitive  test.  Both  were 
fired  with  semi-bituminous  coal  under  regular  working  conditions. 
Examining  the  data  we  find  that  there  were  five  tests  of  the  water-tube 
boiler,  the  rates  of  driving  ranging  from  W/S  =  %A9  to  2.92,  averag- 
ing 2.64  Ibs.  evaporated  from  and  at  212°  per  sq.  ft.  of  heating  sur- 
face per  hour,  and  the  efficiencies  from  71.5  to  77.0%.,  averaging 
73.8%;  while  there  was  only  one  test  of  the  fire-tube  boiler,  with 
W/s  =  3.10,#  =  67.3%.  The  saving  in  this  case  is  not  (73. 8  —  67. 3) -r- 
67.3  =  9.6%,  but  only(73.8  -  67.3)  -f-  73.8  =  8.8%.  In  computing  the 
saving  from  the  figures  of  efficiency,  the  divisor  should  always  be 
the  higher  figure.  The  only  conclusion  that  should  be  drawn  from 
these  tests  is  that  the  fire-tube  boiler  gave  a  result  considerably  lower 
than  it  should  have  given  with  proper  firing,  a  clean  boiler,  no 
air  leaks  in  the  setting,  and  a  sufficiently  large  back  connection  to 
insure  that  the  hot  gases  flowed  uniformly  through  all  the  tubes. 

Another  set  of  tests  with  the  same  type  of  .water-tube  boiler  gave  us 
an  average  of  five  tests  W/S  =  3.11,  £=72%,  as  compared  with  the 
result  from  another  type  of  water-tube  boiler,  TF/#.=  3.37,  E  =  64,5%. 
The  coal  was  the  same,  a  high  grade  of  semi-bituminous.  No  in- 
formation is  given  about  the  furnace  with  which  the  other  type 
was  equipped;  it  may  have  been  an  anthracite  furnace.  The  falling 
off  of  7.5%  efficiency  should  not  have  been  considered  the  fault  of 
the  other  water-tube  boiler  itself,  but  of  some  conditions  of  the 
furnace  or  of  firing,  air  leaks,  damaged  baffling  walls,  or  other  cause. 

Great  care  should  be  used  in  drawing  conclusions  from  the  results 
of  comparative  boiler  tests  made  with  and  without  the  use  of  some 
special  appliance.  If  a  test  made  to  prove  that  a  certain  device  inT- 
proves  the  efficiency  of  a  boiler  gives  a  figure  of  70  per  cent  when  it  is 
used  and  only  60  per  cent  when  it  is  not,  it  by  no  means  follows  that 
the  use  of  the  device  was  the  cause  of  the  apparent  improvement. 
Some  slight  change  in  the  method  of  firing,  in  the  thickness  of  the 
coal  bed,  or  in  the  force  of  the  draft,  may  have  caused  all  the  difference, 
and  more  than  70  per  cent  might  have  been  obtained  without  the 
device,  under  proper  conditions  of  firing  and  draft. 

Vertical    versus    Horizontal    Baffling    of   Water-tube    Boilers. — 

Kreisinger  and  Ray  (Power,  August  19,  1913),  Describe  a  series  of 
tests  with  two  kinds  of  coal  to  determine  whether  horizontal  or  ver- 
tical baffles  in  a  Babcock  &  Wilcox  type  of  boiler  gave  the  highest 
efficiency.  The  principal  average  results  were  as  follows : 

The  coals  were  Pocahontas,  W.  Va.,  and  Clinchfield,  Va.,  the 
former  containing  18  and  the  latter  35  per  cent  volatile  matter  in  the 
combustible.  The  authors  conclude  that  the  horizontal  baffling  gives 
much  better  results  than  the  vertical,  and  that  in  the  horizontal 


EVAPORATION  TESTS  OF  STEAM-BOILERS. 


595 


Kind  of  Baffling 

Vertical. 

Horizontal,  2  passes. 

Horizontal,  3  passes. 

Kind  of  Coal  

Semi-bit. 

Bit. 

Semi-bit. 

Bit. 

Semi-bit. 

Bit. 

Number  of  tests  
H.P.  developed,  per  cent  of 

4 

128 
128 
61.3 

3 

114 
158 
60.9 

4 

113 
99 
63.6 

3 

137 
109 
67.2 

3 
119 

2 

122 
102 
69.9 

Efficiency,  boiler  and  grate. 

67.7 

3-pass  boiler  the  draft  over  the  fire  is  considerably  reduced,  hence 
there  is  less  chance  of  drawing  too  much  air  into  the  furnace.  No 
general  conclusion  as  to  the  relative  merits  of  horizontal  and  ver- 
tical baffling  can  be  drawn  from  these  tests.  With  the  vertical 
baffling  there  was  far  too  great  an  excess  of  air,  which  might  have 
been  avoided  either  by  carrying  heavier  fires  or  by  checking  the 
draft  by  the  chimney  damper,  and  the  combustion  chamber  was  far 
too  small,  the  furnace  being  adapted  only  for  anthracite  coal.  With 
the  horizontal  baffling  the  excess  air  supply  was  less,  and  the  com- 
bustion chamber  much  larger. 


CHAPTEK  XVII. 


RESULTS  OF  STEAM-BOILER  TRIALS. 

IN  this  chapter  the  results  of  trials  of  several  different  boilers  will 
be  given,  together  with  comments  which  may  be  useful  to  students  of 
the  subject.  Mere  tables  of  results  of  individual  boiler-tests  are  of  little 
use  until  they  are  collated  and  compared  with  a  view  to  discover  the 
various  causes  or  conditions  which  contributed  to  the  results  obtained. 

Range  of  Economy  found  in  Actual  Practice. — In  Donkin's  "Heat 
Efficiency  of  Steam-boilers"  there  are  fifty  tables  containing  the  results 
of  425  experiments  on  boilers  of  different  types.  The  following  table 
is  a  brief  summary  of  the  highest,  lowest,  and  mean  efficiencies  obtained 
in  405  experiments  with  different  boilers  "without  economizers: 

EFFICIENCY   PER   CENT. 


Type  of  Boiler. 

Number  of 
Experiments. 

|5 

o| 

jl 

S-o 

Lowest,  One 
Experiment. 

Mean  of  All 
Experiments. 

Type  of  Boiler. 

1  Number  of 
Experiments. 

Mean  of  Two 
best  Results. 

Lowest,  One 
Experiment. 

IMean  of  All 
Experiments. 

Water-  tube*.  . 
Locomotive.  .  . 
Lancashire.  .  .  . 
Two-story.  .  .  . 
Two-story.  .  .  . 
Dry-back.    .  .  . 

6 
37 
10 

9 
29 
?4 

84.1 
83.3 
74.4 
76.1 
79.8 
75.7 

66.6 
53.7 
65.6 
57.6 
55.9 
64.7 

77.4 
72.5 
72.0 
70.3 
69.2 
69.2 

Elephant.  .  . 
Water-tube  f 
Lancashire.  . 
Cornish  .... 
Lancashire.  . 
Dry-back.  .  . 

7 
49 
40 
3 
107 
6 

70.8 
77.5 
73.0 
65.9 
79.5 
73.4 

58.9 
50.0 
51.9 
60.0 
42.1 
54.8 

65.3 
64.9 
64.2 
62.7 
62.4 
61.0 

Return  tube  .  . 
Cornish      .... 

11 
?5 

81.2 
81.7 

56.6 
53.0 

68.7 
68.0 

Lancashire  {. 
Elephant.  .  . 

6 

8 

66.7 
65.5 

52.0 
54.9 

59.4 

58.5 

Cornish  
Wet-back  

9 
6 

81.0 
69.6 

55.0 
62.0 

67.0 
66.0 

Lancashire.  . 
Vertical.  .  .  . 

8 
5 

74.3 
76.5 

45.9 
44.2 

57.3 
56.2 

*  1^-in-  tubes.  f  4-in.  tubes.  J  Three-flue. 

About  the  only  conclusions  that  may  be  drawn  from  this  table  are 
that  with  many  different  varieties  of  boilers  there  may  be  obtained 
efficiencies  which  are  so  high  as  to  be  scarcely  credible;  that  with  the 
same  types  of  boilers  in  other  trials  the  results  are  so  low  that  they 
can  only  be  accounted  for  by  improper  firing  or  some  other  unfavorable 
condition;  and  that  economy  does  not  depend  on  the  type  of  boiler. 
In  107  tests  of  Lancashire  two-flue  boilers  the  efficiencies  varied  from 

596 


RESULTS  OF  STEAM-BOILER  TRIALS. 


597 


79.5  down  to  42.1  per  cent,  or  all  the  way  from  nearly  the  highest  pos- 
sible figure  down  to  the  lowest  one  obtained  in  the  whole  series  of  tests. 
In  Mr.  Geo.  H.  Barrus's  book  on  Boiler  Tests  there  are  records  of  a 
great  number  of  tests  with  different  kinds  of  boilers,  with  different  coals, 
and  in  different  parts  of  the  country.  Selecting  those  tests  of  which 
complete  records  are  given,  we  find  the  economy  ranges  as  follows: 


Water  Evaporated  from  and  at  212° 
per  Ib.  Combustible. 

Number  of  Tests 
Anthracite. 

Number  of  Tests 
Semi-bit. 

Number  of  Tests 
Bituminous. 

Over  12  Ibs 

6 

11  5  to  12  Ibs                      .... 

2 

6 

11      to  11  5  Ibs  

10 

5 

10  5  to  11  Ibs  

20 

3 

10      to  10  5  Ibs  

11 

5 

1 

9      to  10  Ibs  

14 

6 

2 

8      to    9  Ibs 

8 

3 

6      to    7  Ibs.                   .... 

1 

66 

34 

3 

Out  of  66  tests  with  anthracite,  only  two  gave  a  result  over  11.5 
Ibs.,  a  figure  which  may  be  reached  with  any  type  of  boiler,  properly 
designed  and  set,  by  a  good  fireman  using  good  coal.  Twenty-three 
out  of  the  66  boilers  gave  a  result  below  10  Ibs.,  or  20  per  cent  less 
than  the  highest  figure  attainable.  In  the  semi-bituminous  tests  only 
six  boilers  out  of  34  gave  12  Ibs.,  a  figure  which  may  easily  be  obtained 
with  any  good  form  of  boiler,  properly  proportioned,  properly  set, 
and  properly  fired. 

Mr.  Barrus's  Later  Tests, — The  tests  referred  to  above  were  made 
between  1878  and  1888.  In  1911  Mr.  Barrus  presented  a  paper  at 
the  Congress  of  Technology,  in  Boston,  in  which  he  gave  the  results 
of  more  than  300  tests  that  he  had  made  since  1888.  Arranging  these 
tests  in  a  similar  table  to  the  one  given  above  we  have  the  following : 


Water  Evaporated  from  and 
at  212°  per  Lb.  Combustible. 
Lbs. 

No.  of  Tests, 
Anthracite. 

No.  of  Tests, 
Mixed  Anth. 
and  Soft. 

No.  of  Tests, 
Semi-bit. 

No.  of  Tests, 
Bituminous. 

over  12 

2 

2 

45 

3 

11.  5  to  12 

2 

37 

2 

11      to  11.  5 

7 

7 

45 

7 

10.  5  to  11 

17 

7 

44 

7 

10     to  10.5 

9 

3 

24 

3 

9      to  10 

6 

3 

7 

17 

8      to    9 

2 

2 

2 

5 

7     to    8 

1 

3 

Total  

45 

25 

204 

47 

598  STEAM-BOILER  ECONOMY. 

This  table  shows  no  improvement  in  anthracite  practice  over  the 
earlier  tests,  probably  on  account  of  the  increasing  use  of  the  finer  sizes, 
high  in  ash  and  moisture,  but  there  is  a  notable  improvement  in  the 
semi-bituminous  tests,  84  per  cent  of  them  showing  an  evaporation 
of  over  10.5  Ibs.  as  compared  with  59  per  cent  in  the  first  table.  This 
improvement  is  no  doubt  due  to  the  use  of  improved  furnaces  and 
mechanical  stokers.  A  study  of  the  results  of  these  later  tests  leads  to 
the  following  conclusions: 

1.  Economy  does  not  depend  on  the  type  of  boiler. 

2.  With  anthracite  coal  no  special  furnace  is  needed. 

3.  With  semi-bituminous  coal  high  economy  is  obtained  with  an 
ordinary  furnace  in  only  a  few  cases,  in  which  the  firing  is  exception- 
ally good,  and  generally  high  results  are  obtained  only  with  special 
fire-brick  furnaces  or  mechanical  stokers. 

4.  High  economy  combined  with  high  rate  of  driving  can  be  ob- 
tained, only  when  all  conditions  are  most  favorable,  including  the 
regulation  of  air  supply  according  to  the  analysis  of  the  chimney 
gases. 

5.  The  ordinary  practice  with  volatile  bituminous  coals  is  much 
poorer  than  it  should  be,  but  high  results  are  obtainable  with  mechan- 
ical stokers. 

Tests  of  Stirling  Boilers  with  Anthracite  Coal,*— In  1894  Mr. 
Geo..  H.  Barrus  made  a  series  of  nine  tests  on  two  Stirling  water-tube 
boilers  at  two  colleries  near  Wilkes-Barre,  Pa.  From  the  reports 
of  these  tests  the  diagram  and  table  on  pages  599  and  601  have  been 
prepared.  Tests  Nos.  1  and  2  inclusive  were  made  on  a  125-H.P. 
boiler  at  No.  5  shaft  of  the  Lehigh  and  Wilkes-Barre  Coal  Co.,  and 
Nos.  8  and  9  were  made  on  a  150-H.P.  boiler  at  the  Dorrance  colliery 
of  the  Lehigh  Valley  Coal  Co.  The  rating  of  the  boilers  is  on  the 
basis  of  11-|  sq.  ft.  of  heating  surface  to  a  horse-power.  Forced  draft 
was  supplied  by  McClave  steam-blowers.  The  coal  used  in  the  several 
tests  differed  in  size  and  quality.  The  sizes  were  determined  by  pass- 
ing samples  through  and  over  screens  of  different  meshes  and  weigh- 
ing the  portions  thus  separated.  The  coal  used  in  five  of  the  tests  was 
as  shown  in  the  table  on  p.  599,  the  figures  being  given  in  percentages. 

A  Study  of  the  Results  of  the  Stirling  Tests. — For  comparing  the 
results  of  these  tests  they  have  been  plotted  on  the  accompanying 
diagram,  Fig.  255,  showing  the  relation  of  the  water  evaporated  per 

.  *  From  Mines  and  Minerals,  December,  1897. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


599 


Sizes  of  Screen. 

Over  &. 

Through 
A 

Through 

Through 
A- 

Through 
H- 

Test  No.  3.  No.  2  buckwheat  .  . 
"      *  '    6.  Culm,  No.  5  shaft  . 
lt      "7    Culm  No  4  shaft 

25 

18 

45 
3 
24  1 

19 
11 

11 

86 
57  9 

"      "8.  No.  2  buckwheat  .  . 

2.5 

65 

32.5 

"      "    9.  No  2  buckwheat 

10  7 

67 

22  3 

pound  of  combustible,  or  the  economy,  to  the  rate  of  driving,  or  the 
water  evaporated  per  square  foot  of  heating  surface  per  hour.  For 
further  comparison  there  are  also  plotted  two  dotted  lines  represent- 


Lds.  Watte  Evaporated  from  and  at  2/2'peistL  Combustible, 
o»  x>  ^  ^  *S 

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12                   345                   6 

Lbs.  Water  Evaporated  per  s<f.  ft.  of   Heating-  Surface  per  Hour. 

FIG.  255. — TESTS  OF  STIRLING  BOILERS  WITH  ANTHRACITE  BUCKWHEAT  AND 
CULM  COMPARED  WITH  TESTS  RECORDED  IN  BARRUS  ON  "BOILER  TESTS" 
AND  WITH  THE  CENTENNIAL  TESTS. 

ing  the  maximum  and  the  average  results  of  tests  with  anthracite 
coal  given  in  Mr.  Barrus's  book  on  "Boiler  Tests,"  together  with  a  line 
representing  the  maximum  results  obtained  in  the  boiler-tests  at  the 
Centennial  Exhibition.  As  the  Centennial  tests  were  made  with  egg 
coal  of  excellent  quality  and  under  the  most  favorable  conditions,  it  is 
to  be  expected  that  their  maximum  results  will  be  considerably  above 
those  obtained  with  buckwheat  coal.  Of  the  tests  with  buckwheat  coal 
given  in  the  above  table,  Nos.  3,  4,  and  5  lie  close  to  the  line  of  Mr. 
Barrus's  maximum  results,  Nos.  8  and  9  are  near  the  line  of  his 
average  results,  and  No.  1  is  considerably  below  the  average  line.  Of 
the  tests  with  culm,  No.  6  is  a  little,  and  No.  7  considerably,  below 


600  STEAM-BOILER  ECONOMY. 

the  average  line,  while  test  No.  2,  with  one-fourth  buckwheat  and 
three-fourths  culm,  is  far  below  the  average  line.  In  explanation  of 
these  varied  results  we  find  on  referring  to  Mr.  Barrus's  report  that 
in  tests  Nos.  1,  2,  and  3  the  shaking  grate-bars  had  their  air-spaces 
unevenly  adjusted,  causing  an  uneven  distribution  of  air  through  the 
bed  of  coal.  This  may  account  to  some  extent  for  the  low  results  of 
tests  Nos.  1  and  2,  but  it  does  not  seem  to  have  had  much  effect  in 
test  No.  3,  the  result  of  which  is  very  high.  The  three  tests  were 
made  on  three  consecutive  days,  and  possibly  in  test  No.  1  the  firing 
was  done  unskilfully,  for  the  temperature  of  the  gases  was  beyond 
the  range  of  the  thermometer,  or  over  800°,  and  during  the  whole 
run  the  flame  from  the  coal  extended  into  the  stack  and  during  part  of 
the  time  flame  could  be  seen  issuing  from  the  top  of  the  stack.  Over- 
driving of  the  boiler  does  not  sufficiently  account  for  this,  for  in  test 
No.  5  with  the  same  coal  (or  nearly  the  same)  as  in  No.  1  and  with 
the  boiler  developing  as  great  a  horse-power  the  temperature  of  the 
flue-gases  averaged  only  684°.  Test  No.  2,  with  three-fourths  culm 
and  on'e-fourth  buckwheat,  gave  a  result  over  12  per  cent  below  test 
No.  6,  all  culm,  the  boiler  in  the  two  tests  being  driven  at  the  same 
rate.  This  loss  of  12  per  cent  may  have  been  due  to  mal-adjustment 
of  the  grate-bars,  but  it  was  probably  partly  due  to  the  mixing  of 
two  kinds  of  coal,  which  is  generally  believed  to  give  poor  results 
with  anthracite  coal,  the  fine  sizes  choking  up  the  interstices  between 
the  larger  sizes,  and  doing  this  irregularly  on  different  portions  of  the 
grate,  causing  irregular  burning,  with  excess  of  air-supply  through 
some  portions  and  deficient  supply  through  others. 

Tests  Nos.  1  and  5,  with  the  same  coal  and  the  same  rate  of 
driving  of  the  boiler,  show  a  remarkable  difference  of  economy,  the 
former  being  over  14  per  cent  below  the  latter.  The  differences  of  the 
conditions  of  these  tests  which  may  have  caused  the  difference  in 
results  were:  (1)  Larger  grate-surface  in  No.  1  than  in  No.  5;  (2) 
bad  adjustment  of  the  air-spaces  in  No.  1;  (3)  possibly,  unskilled 
firing  in  No.  1.  The  larger  grate-surface  in  No.  1  is  not  likely  to 
have  been  the  cause,  for  test  No.  3  with  the  same  large  grate-surface 
gave  practically  as  high  a  result  as  No.  4,  with  the  reduced  grate- 
surface.  The  difference  in  tests  No.  1  and  5  is  instructive  in  showing 
what  a  wide  difference  in  results  is  possible  in  the  same  boiler,  with 
the  same  coal  and  the  same  rate  of  driving,  due  to  what  may  appear 
to  be  slight  causes,  such  as  difference  in  the  air-spaces  through  the 
grate-bars  or  in  the  skill  of  the  fireman. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


TESTS    OF    STIRLING    BOILERS    AT   ANTHRACITE    COAL   MINES. 


601 


Number  of  Test 

l 

2 

3 

4 

5 

Test  for  capacity  or  economy. 

Capacity. 

Capacity. 

Economy. 

Economy 

Capacity. 

Kind  of  coal     .       ...        

Buck- 
wheat. 

Culm,  %. 
Buck- 
wheat Yi. 

Buck- 
wheat. 

Buck- 
wheat. 

Buck- 
wheat. 

Ash  and  clinker,  per  cent  
Area  of  grate  sq.  ft. 

12.0 
45 
31.9 
.16 
1.00 

12.9 
29.3 

6.04 
289.3 
131 

800 
7.563 
8.594 

25.9 
45 
31.9 
.16 
1.00 

14.55 

2.74 
131.3  . 
5.0 

439 
6.910 
9.325 

12.0 

45 
31.9 
.16 
0.20 

7.2 
13.17 

3.61 
172.8 
38.2 

500 
9.955 
11.324 

12.0 
38 
37.8 
.16 
0.30 

6.7 
14.84 

3.33 
159.6 

27.7 

485 
10.  07^ 
11.44? 

12.6 
38 
37.8 
.16 
1.00 

13.3 

28.28 

6.06 
290.2 
132 

684 
9.310 
10.052 

Ratio  of  grate  to  heat'g  surface,  1  to 
Draft-suction  in  stack,  ins.  of  water.  . 
Draft-pressure  in  ash-pit,  ins  
Steam    used    to    run    blowers,    esti- 
mated H.  P  

Coal  burned  per  hour  per  square  foot 
of  grate,  Ibs. 

Water  evaporated  per  hour  per  square 
foot  heating  surface,  Ibs  

Horse-power  developed,  H.  P  
H.  P.  above  boiler's  rating,  per  cent  . 
Average    temperature    of    flue-gases, 
degrees  F.,  about  

Water  evaporated  from  and  at  212° 
per  pound  of  coal  Ibs     .  . 

Water  evaporated  from  and  at  212° 
per  pound  of  combustible.          .  .  . 

Number  of  Test  

6 

7 

8 

9 

Test  for  capacity  or  economy. 

Capacity. 

Capacity. 

Capacity. 

Economy] 

Kind  of  coal 

Culm.  No.  5. 

Culm.  No.  4. 

Buckwheat. 

Buckwheat. 

Ash  and  clinker,  per  cent. 

15.1 
45 

31.9 
.16 
0.90 

8.7 
10.66 

2.81 
134.8 

7.8 

462 
9.122 
10.745 

20.7 
45 

31.9 
.16 
1.00 

12.3 
17.63 

3.79 
181.6 
45.3 

543 
7.889 
9.949 

15.6 
47.3 
36.5 
.12 
1.50 

13.2 
23.82 

4.8 
275.9 
83.9 

560 

8.437 
9.996 

13.9 
47.3 
36.5 
.10 

0.87 

18.16 

3.92 
225.2 
50.1 

524 
9.046 
10.495 

Area  of  grate,  sq.  ft.        

Ratio  of  grate  to  heating  surface,  1  to 
Draft-suction  in  stack,  ins.  of  water.  . 
Draft-pressure  in  ash-pit,  ins  

Steam    used    to    run    blowers,    esti- 
mated H.  P. 

Coal  burned  per  hour  per  square  foot 
of  grate,  Ibs  

Water  evaporated  per  hour  per  square 
foot  heating  surface,  Ibs  

Horse-power  developed,  H.  P  
H.  P.  above  boiler's  rating,  per  cent  . 
Average    temperature    of    flue-gases, 
degrees  F.  about  .  .  :  
Water  evaporated  from  and  at  212° 
per  pound  of  coal,  Ibs  

Water  evaporated  from  and  at  212° 
per  pound  of  combustible. 

Tests  Nos.  8  and  9  fall  considerably  below  the  line  of  tests  Nos. 
3,  4,  and  5.    These  tests  were  made  on  a  different  boiler  of  the  same 


602  STEAM-BOILER  ECONOMY. 

make,  but  there  was  probably  not  any  difference  in  the  details  of  con- 
struction of  the  boiler  or  setting  which  would  account  for  the  differ- 
ence in  results.  There  was,  however,  considerable  difference  in  the 
coal,  as  shown  by  the  percentage  of  ash  and  by  the  table  of  sizes.  The 
coal  used  in  Nos.  8  and  9  was  finer  in  size  than  that  used  in  test 
No.  3,  66  per  cent  of  it  going  through  a  ^-in.  screen,  while  in  the  coal 
of  test  No.  3  only  30  per  cent  went  through  14-in.  The  coal  of  tests 
Nos.  8  and  9  was  of  an  intermediate  size  between  that  of  test  No.  3 
and  culm,  and  the  diagram  shows  that  the  results  given  by  it  are  also 
intermediate  between  those  of  the  other  coals. 

The  results  plotted  in  the  diagram  are  the  pounds  of  water 
evaporated  per  pound  of  combustible  and  not  per  pound  of  coal.  Since 
the  combustible  of  all  the  coals  used  in  these  tests  is  practically  of 
identical  quality,  it  might  be  expected  that  all  the  coals  would  give 
the  same  result  per  pound  of  combustible,  and  that  results  per  pound 
of  coal  would  correspond,  except  as  they  are  influenced  by  different 
percentages  of  moisture  and  ash.  The  plotted  results  show,  however, 
that  although  the  combustible  portion  of  all  the  coals  may  be  identical 
in  quality,  it  gives  different  results  when  it  is  contained  in  coal  of 
different  sizes.  Tests  Nos.  3,  4,  and  5,  with  the  largest  size  of  buck- 
wheat coal,  give  the  best  results,  tests  Nos.  8  and  9  with  finer-sized 
buckwheat  give  results  much  lower,  and  tests  Nos.  6  and  7,  with 
culm,  still  lower  results.  Tests  Nos.  1  and  2,  both  exceptionally  low, 
may  be  neglected  from  the  comparison,  as  they  were  influenced  by 
unfavorable  conditions,  such  as  mixing  of  sizes  and  uneven  adjustment 
of  the  air-spaces.  The  best  results  obtained  with  the  large-sized 
buckwheat  coal,  also,  are  from  5  to  7  per  cent  below  the  best  results 
obtained  in  the  Centennial  tests  with  egg  coal. 

A  reasonable  theory  to  account  for  the  regular  decrease  in  evapo- 
ration per  pound  of  combustible  as  the  size  of  the  coal  is  made  finer 
seems  to  be  the  following :  When  egg  or  other  large-sized  coal  is  used, 
a  thick  bed  of  it  is  carried  on  the  grate,  through  which  the  air  passes 
with  comparative  uniformity.  The  lumps  of  coal  burn  away  slowly, 
from  the  surface ;  fresh  coal  is  fired  at  long  intervals  of  time,  and  the 
condition  of  the  fire  is  always  nearly  the  same.  If  the  draft  and  the 
thickness  of  the  bed  are  properly  related  to  each  other,  and  the  boiler 
is  well  designed,  the  maximum  economy  possible  with  the  coal  may 
be  obtained.  With  finer-sized  coals,  however,  a  thinner  bed  must  be 
carried,  relatively  to  the  force  of  draft ;  air-holes  are  more  likely  to  be 
formed  in  the  bed,  causing  too  great  a  supply  of  air  to  pass  through 


RESULTS  OF  STEAM-BOILER   TRIALS.  603 

some  portions  while  an  insufficient  supply  is  furnished  to  other  por- 
tions. Fresh  coal  is  fired  at  frequent  intervals,  involving  frequent 
openings  of  the  doors  and  inrush  of  cold  air;  and  the  fresh  coal  for  a 
short  time  after  firing,  being  small  in  size,  is  apt  to  clog  the  fire  and 
obstruct  the  air-supply,  causing  the  burning  of  the  coal  to  carbonic 
oxide  instead  of  carbonic  acid.  The  bed  of  coal  being  thin  and  the 
draft  strong,  if  the  fireman  leaves  the  fire  unattended  to  for  a  minute 
or  two  after  it  is  time  to  fire  fresh  coal,  air-holes  will  form  rapidly, 
while  with  egg  coal  a  period  of  five  minutes  makes  but  little  differ- 
ence. 

The  results  of  these  tests  show  that  the  efficiency  of  any  given 
steam-boiler  is  not  a  constant  quantity,  that  it  varies  not  only  with 
the  rate  of  driving,  but  with  the  quality  of  the  coal  and  even  with  the 
size  of  coal  of  the  same  quality. 

Another  useful  lesson  to  be  learned  from  these  tests  is  in  regard 
to  the  capacity.  The  three  capacity-tests  with  buckwheat  coal,  Nos. 
1,  5,  and  8,  gave  a  horse-power,  respectively,  131,  132  and  84  per 
cent  above  the  rated  power  of  the  boiler,  and  the  highest  economy 
was  obtained  when  the  boiler  was  driven  28  per  cent  above  its  rating. 
Whether  any  higher  economy  could  have  been  obtained  with  this  coal 
if  the  boiler  had  been  driven  at  a  lower  rate  cannot  be  said,  for  no  test 
was  made  at  a  lower  rate  with  buckwheat  coal.  The  three  capacity- 
tests  with  culm,  Nos.  4,  6,  and  7,  gave  respectively  5,  8,  and  45  per 
cent  above  rating  although  the  force  of  draft  was  practically  the  same 
as  in  the  tests  with  buckwheat  coal.  It  appears  then  that  a  boiler 
will  not  develop  the  same  horse-power  from  culm  as  from  buckwheat 
unless  the  grate-surface  or  the  draft  or  both,  are  increased. 

Comparative  Trials  on  Three  Two-flue  Boilers  with  Pittsburg  Coal. 
— These  tests  were  made  by  the  Shoenberger  Steel  Co.,  Pittsburg, 
Pa.,  in  1897,  to  determine  the  efficiency  of  the  American  Underfeed 
Stoker  as  compared  with  flat  grates  when  applied  to  two-flue  boilers. 

The  results  of  these  tests  are  of  interest  for  many  reasons.  The 
hand-fired  test  is  fairly  representative  of  what  was  every-day  practice 
with  the  two-flue  boiler  in  the  Pittsburg  iron-mills  until  the  general 
introduction  of  water-tube  boilers  and  improved  furnaces  and  methods 
of  firing.  In  this  test  the  boiler  was  driven  at  2.73  times  its  rated 
power,  the  flue-gases  escaped  at  816°  F.,  and  the  calculated  efficiency 
is  only  43.3  per  cent.  In  the  "economy"  test,  so-called,  with  the 
stoker,  the  boiler  was  driven  at  a  still  higher  rate  of  evaporation,  viz., 
3.05  times  its  rated  power,  although  less  coal  was  burned  under  it, 


604 


STEAM-BOILER  ECONOMY. 


Grate-surface,  total  of  three  boilers,  90  sq.  ft.;  water-heating  surface,  1225  sq.  ft. 
ratio  of  heating  to  grate-surface,  13.6. 


Hand  fire 

America 

a  Stoker. 

Economy. 

Capacity. 

Duration,  hours   

8 

8 

7 

Steam-pressure  by  gage,  pounds  
Temperature  of  excaping  gases,  °F.  .  . 
1  '            '  •  '  feed  water,  °F  

101.2 
816.3 
149  9 

101.09 
735.1 
155  9 

99.24 
828 
171  3 

Size  of  coal   

Run  of  Mine 

River  Slack 

River  Slack 

Quantity  of  coal  consumed,  pounds  .  . 
Refuse,  per  cent  
Coal  per  sq.  ft.  of  grate  per  hour,  Ibs. 
Total  water  actually  evaporated,  Ibs. 
Water  per  hour,  equivalent  from  and 
at  212°  F.,  pounds  

13,500 
12 
18.7 
82,160 

11,344 

10,500 
9.49 
14.5 
92,140 

12,653 

12,300 

19.4 
100,917 

15600  3 

Water  per  hour,  per  square  foot  heat- 
ing surface,  pounds   

9.26 

10  33 

12  73 

Evaporation,    apparent    per    Ib.    of 
coal  Ibs  

6  086 

8  775 

8  204 

Evaporation,  from  and  at  212°  F.,  Ibs. 
Horse-power  developed  

6  72 

327.8 

9.640 

360  7 

8.877 
452 

Builders'  rating  

120 

120 

120 

Ratio  of  H.P.  developed  to  builders' 
rating  

2.73 

3.05 

3  7 

Heating  surface  per  horse-power, 
sq.  ft   

3.72 

3.34 

2  7 

Per  cent  increase  of  capacity  by  the 
use  of  stoker  

11  6 

37  5 

Per  cent  increase  evaporation  per  Ib. 
of  coal  as  shown  by  the  American 
Stoker  over  hand-firing 

44  5 

32 

Efficiency,  assuming  the  heating  value 
perlb.  combustible  at  15,000  B.T.U., 
per  cent  

43.3 

62  1 

57  2 

the  temperature  of  the  flue-gases  was  only  735°,  and  the  efficiency 
was  brought  up  to  62.1%.  This  is  a  very  high  efficiency  for  such  a 
rate  of  driving,  but  it  could  no  doubt  have  been  brought  up  to  72 
per  cent  if  the  rate  of  driving  had  been  reduced  about  half  and  the 
temperature  of  the  gases  had  thereby  been  reduced  to  below  500°.  In 
the  capacity-test  with  the  stoker,  still  more  coal  per  hour  was  burned 
than  in  the  hand-fired  test,  and  the  rate  of  driving  was  the  extraor- 
dinary figure  of  12.73  Ibs.  from  and  at  212°  per  sq.  ft.  of  heating 
surface  per  hour,  or  3.7  times  the  rated  power,  yet  the  temperature 
of  the  flue-gases,  828°,  was  only  a  trifle  higher  than  in  the  hand-fired 
test,  while  the  efficiency,  57.2  per  cent,  was  very  much  higher.  The 
results  of  the  test  show  the  advantage  gained  by  the  short  flame  of 
very  high  temperature  produced  by  the  American  stoker  with  its  forced 


RESULTS  OF  STEAM-BOILER   TRIALS.  605 

blast,  over  the  long  smoky  flame  of  comparatively  low  temperature 
produced  in  the  ordinary  furnace  by  hand-firing  and  natural  draft. 

Applying  to  the  results  of  these  tests  the  "criterion"  formula  given 
in  the  chapter  on  Efficiency  of  Heating  Surface,  page  296,  viz., 

K  -  4.8*  23.04       W 


970(1  +Q.1S/W)  (K  -  4.80  S  ' 

we  obtain,  taking  K  as  15,000 

for  W/S  =  9.26  10.33  12.73 

Ea  =  6.72  9.64  8.877 

a  =  457  244  234 

The  last  two  values  of  a,  244  and  234,  represent  fairly  good  perform- 
ance. The  high  value  of  a,  457,  represents  poor  performance,  which 
is  accounted  for  by  incomplete  combustion  due  to  an  unsuitable 
furnace. 

Test  of  One  of  the  Babcock  &  Wilcox  Boilers  for  the  IT.  S,  Cruiser 
"Cincinnati." — In  the  Annual  Report  of  the  Chief  of  Bureau  of  Steam 
Engineering,  for  1900,  there  is  published  a  report  of  a  test  made  on 
one  of  the  new  boilers  built  by  the  Babcock  &  Wilcox  Company  for 
the  Cincinnati,  by  a  board  composed  of  Lieutenant  Commander  A.  B. 
Willits  and  Lieutenant  B.  C.  Bryan,  TJ.  S.  Navy. 

Description  of  Boiler  and  Appurtenances. — The  boiler  is  com- 
posed entirely  of  wrought  steel,  the  point  of.  difference  between  it  and 
the  older  type  of  this  make  of  boiler  being  in  the  arrangement  of 
baffle-plates  (as  shown  in  the  sectional  view,  Fig.  140,  p.  373,  which 
compel  the  products  of  combustion  to  pass  three  times  across  the  tubes 
before  entering  the  uptake.  The  small  tubes  are  2  ins.  outside  diam- 
eter, while  the  bottom  tube  in  each  section  or  element  is  4  ins.  outside 
diameter. 

BOILER   DATA. 

Diameter  of  top  drum,  42  ins.  (inside). 

Length  of  top  drum,  12  ft. 

Tubes:    Number,  526;    2  ins.  outside  diameter;    length,  8  ft.     Also  40;    4  ins. 
outside  diameter;  length,  8  ft.  5f  ins. 

Grate-surface:  Length,  6  ft.  8|  ins.;  width,  9  ft.  5£  ins.;  area,  63.25  sq.  ft. 

Grate  surface  reduced  to  5  ft.  6  ins.  length,  52  sq.  ft.  area,  in  tests  Nos.  5  and  6. 

Heating  surface:  Area,  2640  sq.  ft.;  ratio  to  grate,  41.74  :  1. 

Smoke-pipe:  Area,  7.876  ft.;  height,  48  ft.  above  grate;  ratio  to  grate,  1  :  8.03. 

Weight  of  boiler  and  all  fittings  except  uptakes  and  smoke-pipe: 

Without  water,  Ibs 53,304 

With  water,  5  ins.  in  glass;  steam  at  215  Ibs.,  Ibs 62,802 

Total  weight  per  sq.  ft.  of  grate-surface,  Ibs 992.9 

Total  weight  per  sq.  ft.  of  heating  surface,  Ibs 23 . 79 

Weight  of  air-heater  and  ducts,  Ibs 5,320 


606  STEAM-BOILER  ECONOMY. 

Blower  fan,  Sturtevant;  diameter,  60  ins.;  driven  by  belt  from  shop  engines. 
Area  of  blower  inlet,  9.62  sq.  ft.;  oultet,  6.89  sq.  ft. 
Air-heater:  Two-pass;  3  in.  tubes.     Area  of  surface,  495  sq.  ft. 

Description  and  Object  of  Tests. — Seven  tests  were  made  in  all. 
Six  of  these  consisted  of  three  pairs  in  which  the  two  tests  of  each  pair 
were  under  similar  conditions  in  every  way  except  that  of  using  the 
air-heater,  one  being  with  and  the  other  being  without  this  heater,  in 
order  to  define  the  economy  due  to  its  use.  The  last  or  seventh  test 
was  for  the  maximum  consumption.,  and  was  made  without  the  air- 
heater  and  with  full  grate.  Two  pairs  of  tests,  one  at  a  consumption 
of  about  20  Ibs.  of  coal  and  the  other  at  about  35  Ibs.  of  coal  per  square 
foot  of  grate  per  hour,  were  made  with  the  full  grate  surface  in  use. 
These  tests  will  be  found  in  tables  of  results  numbered  1,  2H,  3H,  4, 
the  letter  H  signifying  that  the  air-heater  was  in  use  during  the  tests. 
Tests  1  and  2H  were  of  eight  hours'  duration,  and  tests  3H  and  4 
were  of  six  hours'  duration.  The  grate-surface  was  then  reduced  to  52 
sq.  ft.  by  a  course  and  a  half  of  bricks,  seven  courses  in  height,  at  back 
of  furnace,  and  tests  Nos.  5  and  6H,  lasting  four  hours  each,  were 
made,  burning  about  50  Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour.  The 
bricks  were  then  removed  from  the  furnace  and  test  No.  7,  lasting 
three  and  one-third  hours,  was  made,  burning  nearly  60  Ibs.  of  coal 
per  sq.  ft.  of  grate  per  hour.  The  data  and  results  of  these  tests  will 
be  found  in  the  accompanying  tables. 

.Coal  and  Firing. — The  coal  used  was  Pocahontas  coal  from  Flat 
Top  Mine.  It  contained  considerable  slate  and  clinkered  badly.  On 
tests  Nos.  1  and  2H  run-of-mine  coal  was  used;  on  tests  Nos.  3H,  4,  5; 
and  6H  the  coal  was  screened,  using  a  screen  with  a  1-inch  mesh.  On 
test  No.  7  the  screenings  from  the  former  tests  were  run  over  a 
%-inch  mesh  screen,  and- the  coal  thus  screened  was  mixed  with  the 
screened  coal  used  in  other  tests.  The  firing  was  good  and  very  regu- 
lar. Two  alternate  doors  were  fired  in  rapid  succession.  The  other 
two  sections  of  fires,  in  wake  of  the  other  two  doors,  were  then  levelled 
with  a  hoe,  then  sliced  through  the  slicing  door,  and  then  coaled,  the 
average  time  between  coalings  of  the  same  two  furnaces  being  from 
eight  to  ten  minutes.  The  furnace  doors  were  open  about  twenty-five 
seconds  when  coaling  and  about  ten  seconds  in  levelling.  The  coal 
made  comparatively  little  smoke  except  when  firing  or  working  fires. 
The  data  in  regard  to  smoke  were  taken  by  using  Eingelmann  charts. 

Tests  of  a  Thornycroft  Boiler.— Prof.  A.  B.  W.  Kennedy,  in  Proc. 
Inst.  C.  E.,  vol.  xcix  p.  57,  1890,  reports  the  results  of  four  tests  of 
a  Thornycroft  boiler.  The  principal  figures  are  shown  in  the  table  on 
page  609. 

Heating  value  of  the  coal  by  Prof.  Kennedy's  calculation  from 
the  analysis :  14,900  B.T.TJ.  per  Ib. ;  by  direct  calorimetric  determina- 
tion, 15,450  B.T.U.  per  Ib. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


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608 


STEAM-BOILER  ECONOMY. 


ANALYSES   OF  WASTE  GASES  MADE  DURING  TESTS   OF   U.   S.   S. 
"CINCINNATI"  BOILER,  ELIZABETHPORT,  N.  J.,  JUNE,  1900. 


Date. 

?ime. 

Condition  of  fire  when  sample  was  taken. 

CO" 

0 

CO 

'ounds  dry 
gas  pei- 
Pound 
Carbon. 

1900. 
( 

4  58 

15.2 

3.3 

1.0 

5  15 

14  3 

3  0 

2  0 

5  30 

13  0 

6  5 

0  0 

June  15-4 

5  55 

One  minute  after  firing         .... 

12  5 

6  7 

0  8 

6  16 

14  3 

3  7 

1  0 

6  27 

Two  minutes  after  firing              '          .... 

12  7 

6  6 

0  7 

}•    16.8 

i 

7.05 

Three  minutes  after  raking  and  just  be- 
fore firing.  ...               .... 

16.0 

2  0 

2  0 

Average  

14.0 

4.5 

1.1 

j 

f 

11  45 

13  4 

6  4 

0  0 

1 

12  50 

12  0 

5  0 

1  0 

j 

June  16^ 

1  50 

Just  after  slicing        

12  0 

6  6 

0  2 

I 

3.50 

Just  after  slicing  
Average  

13  2 

12.7 

4.8 
5.7 

0.7 
0.5 

-     19.1 

f 

11.25 

One-half  minute  after  firing  

12.3 

3  4 

2.T 

1 

1 

12  40 

While  slicing 

14  2 

4  o 

0  1 

June  18-4 

12.50 

Just  after  slicing        

12  5 

4.3 

1.2 

12  58 

13  0 

4  o 

3  4 

}•    17.3 

i 

1  03 

One  minute  after  firing  

13.5 

5  4 

0  2 

Average  

13.1 

4.2 

1.5 

) 

10  10 

While  slicing 

15  0 

3  2 

1  2 

•) 

10.25 
10  °8 

While  slicing  (all  samples  except  1  1  o'clock 
collected  through  J-inch  iron  pipe),  .   . 

13.8 
14  4 

5.2 
3  1 

0.6 
0  9 

10.35 

One  minute  before  firing  

13  2 

5  6 

0  4 

11.00 

While  slicing  (sample  collected  through 
glass  tube)  ....                   .... 

13  0 

5  6 

0  6 

[     18.8 

2  20 

10  2 

8  3 

0  5 

2  40 

Just  after  firing.  ...               

10  2 

9  0 

0  3 

| 

Average                    ....                  . 

12  8 

5  7 

0  6 

J 

r"1 

10  25 

While  slicing                       . 

i3  5 

K  7 

0  0 

11  00 

While  slicing    

11  2 

8  4 

0  3 

1 

11  04 

10  4 

81 

0  *> 

June  20<{ 

11  13 

Two  minutes  before  raking              .... 

9  2 

9  9 

0  0 

1 

I 

12.25 

Just  after  raking  

12  1 

5  4 

0  7 

v    20.6 

I 

12  36 

Just  after  raking  .... 

14  2 

4  0 

0  8 

Average      .                      

11  8 

6  9 

0  4 

j 

f 

11  00 

15  7 

4  6 

0  1 

11.03 

One  minute  before  raking  

13  0 

6  0 

0  0 

11   13 

15  4 

8  0 

0  6 

June2H 

11.50 

Just  after  raking  .                       .. 

13  6 

5  6 

0  1 

11  55 

One  minute  before  raking 

13  0 

5  3 

0  4 

i 

11.59 

Just  before  raking    

16  0 

4  2 

0  0 

Average  

14  5 

4.8 

0.2 

1" 

11  21 

Two  minutes  before  firing  .        

14  8 

4  g 

1  i 

11.45 

Two  minutes  before  firing  

11  0 

9  0 

0  0 

12.38 

Just  before  levelling  and  firing  

2.26 

Just  after  firing  

11  8 

7  9 

0  4 

18  fi 

2.30 

Just  after  firing              .  .               . 

13  3 

4  2 

1   0 

2.43 

Two  minutes  before  firing  

14  2 

3  8 

1  0 

Average  

12^9~ 

5.8 

0.7 

f 

10  16 

Just  before  firing  

15  3 

4  i 

1  0 

1 

10  21 

13  0 

6  0 

1  0 

June  25  4 

11.10 

Just  after  levelling  

13  7 

6  6 

0  3 

1 

11  13 

Just  after  firing  . 

14  0 

5  2 

00 

\.     18.5 

( 

11  47 

9  o 

112 

00 

Average  

13.0 

iuT" 

0.7~ 

RESULTS  OF  STfJAM-BOILER    TRIALS. 


609 


Trial  No. 

1 

2 

3 

4 

Heating  surface  so  ft                   

1837 

1837 

1837 

1837 

Grate-surface  SQ.  ft            

26  2 

30 

30 

26  2 

Ratio  H.  S  to  G.  S  

70  1 

61  2 

61  2 

70  1 

Steam-pressure,  Ibs   

182 

171 

149 

180 

Temperature  of  air.      .  .        

69 

70 

60 

62 

Coal  per  sq.  ft.  of  grate  per  hr.,  Ibs   

7.74 

18  60 

29  80 

66  80 

Water  per  sq.  ft.  of  H.  S.  per  hr.,  Ibs.  ...... 
Temperature  of  gases  in  chimney  

1.24 
421 

3.20 
540 

4.70 
610 

8.50 

777 

Evaporation  from  and  at  212°  per  Ib.  of  coal 
Efficiency  of  boiler.                  

13.4 

86  8 

12.48 
81  4 

12.00 
78  2 

10.29 
66  6 

Analyses  of  gases,  mean: 
Carbon  dioxide,  CO2       

11  74 

11  68 

12  60 

Carbon  monoxide,  CO  

0.10 

0  62 

2  30 

Oxygen              

7.71 

7  41 

4  45 

Nitrogen,  by  difference  
Air  used  per  Ib  fuel  Ibs. 

80.45 
18  14 

(est    17  8) 

80.29 
17  4 

80.65 
17  2 

Heat  balance: 
Heat  absorbed  by  boiler. 

86  8 

81  4 

78  2 

66  6 

lost  in  chimney  gases          .  . 

10  8 

15  0 

16  5 

20  3 

lost  by  formation  of  CO.  . 

0  5 

1        o    a   / 

5  0 

9  2 

lost  by  radiation  and  unaccounted  for 

1.9 

}    .'•"{ 

2.3 

3.9 

100.0 

100.0 

100.0 

100.0 

Analysis  of  the  coal : 

Moisture 0.96 

Ash 2.19 

Carbon 87. 76 

Hydrogen 4.11 

Oxygen,  nitrogen,  and  sulphur 4 . 98 


100.00 


vrflomytroi 


JTes&. 


^ 


— o  D  IDCOCK  &  Wilcox  ests. 


3          A  5          6  7  8  9          10         II  12         13         14 

Lbs  of  Water  Evaporated  from  and  at  2I2°F.  persq/ft.of  Heating  Surf  perHour. 

FIG.  256. — THORNYCROFT  AND  BABCOCK  &  WILCOX  TESTS  COMPARED. 

The  record  of  the  Thornycroft  test  No.  1,  showing  86.8  per  cent 
efficiency,  probably  contains  some  error.  The  test  was  only  of  five 
hours'  duration,  and  only  1006  Ibs.  of  coal  was  burned  in  the  whole 
test.  A  slight  error  in  the  measurement  of  coal  or  water,  and 


610  STEAM-BOILER  ECONOMY. 

especially  an  error  due  to  fluctuation  of  the  water-level,  would  make 
an  important  error  in  the  result  at  this  very  low  rate  of  driving. 

The  relation  of  the  efficiency  to  the  rate  of  driving  in  the  Bab- 
cock  &  Wilcox  and  the  Thornycroft  tests  is  plotted  in  the  diagram, 
Fig.  256.  There  are  also  plotted,  for  comparison,  a  line  representing 
the  maximum  theoretical  performance  of  a  boiler  in  which  there  is 
no  loss  by  radiation,  calculated  by  means  of  formula  (16),  page  296, 
with  /,  or  pounds  of  dry  gas  per  pound  of  carbon  =  20,  a  —  200, 
t  =  300,  and  K  =  15,750,  no  account  being  taken  of  the  loss  of  heat 
due  to  superheated  steam  in  the  chimney-gases;  together  with  a  line 
representing  the  same  data  but  with  a  radiation  factor  of  R  =  0.1. 
The  record  of  the  seven  best  tests  made  at  the  Centennial  Exhibition, 
taken  from  the  diagram  Fig.  77,  p.  299,  is  also  shown. 

A  Study  of  the  Gas  Analyses  of  the  "Cincinnati"  Tests, — The 
table  on  page  608  shows  considerable  variation  in  the  composition  of 
the  gases  at  different  periods.  This  is  unavoidable  with  hand-firing 
of  semi-bituminous  coal  on  account  of  the  tendency  of  the  coal  to 
cake  shortly  after  firing,  and  thus  obstructing  the  passage  of  air 
through  the  bed.  With  mechanical  stokers  and  large  combustion 
chambers,  giving  facilities  for  a  thorough  mixing  of  the  air  and  gases, 
the  variation  would  no  doubt  have  been  much  less.  There  are  some 
anomalies  in  the  list  of  analyses,  for  example,  at  7.05  June  15  and 
11.59  June  21,  the  C02  was  in  both  cases  16.0,  an  unusually  high 
figure,  but  in  the  first  case  the  CO  and  the  0  were  both  2.0,  while 
in  the  second  case  the  0  was  4.2  and  the  CO  0.0.  At  12.58  on  June 
18  the  CO  was  3.4,  while  the  0  was  4.0,  and  in  some  other  instances 
the  CO  is  much  higher  than  would  be  expected  with  the  given 
amount  of  0  present,  indicating  imperfect  mixture  of  a-ir  and  gas 
in  the  furnace.  In  the  following  table  an  attempt  has  been  made  to 
find  the  probable  losses  of  heat  due  to  imperfect  combustion  and  to 
the  weight  of  dry  gas  per  pound  of  carbon  for  different  amounts  of 
C02  and  of  0  in  the  gases.  The  weight  of  dry  gas  per  pound  of 

carbon  is  11C°2  +J *P  +^C.°  +  N),  and  the  heat  loss  is  figured  for 

o(OU    +   \J\J2) 

an  assumed  temperature  of  the  escaping  gases  of  500°  F.  above  the 
atmospheric  temperature,  and  a  specific  heat  of  0.24.  The  loss 
due  to  imperfect  combustion  of  carbon  in  B.T.TJ.  per  pound  of  C 

^  CO  CO 

burned  is  10,150  X  oo  °r  69'5  ^  "^  °f  14'6°° 

B.T.TJ. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


611 


LOSSES   OF  HEAT   CORRESPONDING   TO   DIFFERENT   GAS  ANALYSES. 


Range 
of  0. 

Average 

Lbs. 
Gas 
per 
Ib.  C. 

B.T.U. 
Loss 
Due 
to  Gas. 

Loss 
Due 
to  CO. 

Sum  of 
Losses. 

Excess 
over 
Ideal. 

Excess 
Loss 
per 
cent. 

No.  of 
Cases 
Aver- 
aged. 

0. 

CO. 

CO*. 

4.0 

4.0 

3.4 

13.0 

15.4 

1848 

2101 

3949 

2113 

14.3 

1 

2      to    4.0 

3.4 

1.4 

14.4 

16.0 

1920 

913 

2833 

997 

6.7 

12 

4.1  to    6.0 

5.1 

0.6 

13.6 

17.8 

2136 

426 

2562 

726 

4.9 

19 

6.4to    7.9 

6.8 

0.34 

12.7 

19.4 

2328 

264 

2592 

756 

5.1 

7 

S.lto  11.2 

9.1 

0.27 

10.2 

23.8 

2856 

258 

3114 

1278 

8.6 

7 

CO2 

CO 

O 

High  COz 

15.5 

0.8 

3.5 

15.5 

1860 

497 

2357 

521 

3.5 

7 

16.0 

2.0 

2.0 

14.2 

1704 

1127 

2831 

995 

6.7 

1 

16.0 

0.0 

4.2 

15.3 

1836 

0 

1836 

0 

0 

1 

CO2  13.  5  to  14.9 

O  3.0to4.2 

14.3 

1.0 

3.7 

16.4 

1968 

660 

2628 

792 

5.4 

7 

5.2to  6.6 

13.7 

0.4 

5.6 

17.9 

2148 

284 

2432 

594 

4.1 

5 

CO2  12  to  13.4 

O  3.  4  to  4.8 

12.9 

1.8 

4.1 

16.9 

2028 

1238 

3266 

1430 

9.7 

5 

5.0to  6.7 

12.8 

0.4 

6.0 

19.0 

2280 

304 

2584 

748 

5.1 

13 

COz  below  12 

O  7.9  to  11.2 

10.4 

0.3 

9.0 

23.4 

2808 

284 

3092 

1256 

8.7 

8 

The  ideal  loss  is  taken  to  be  1836  B.T.U.  or  that  corresponding 
to  the  unusual  analysis  of  C02,  16;  CO,  0.0;  0,  4.2.  The  excess 
of  the  other  losses  over  that  figure  is  divided  by  14,800  B.T.U.,  the 
heating  value  of  1  Ib.  C,  to  obtain  the  percentage  loss  above  the  ideal. 

An  inspection  of  the  above  table  shows  that  the  lowest  excess 
losses,  ranging  from  3.5  to  5.4  per  cent,  correspond  to  C02  ranging, 
in  averaged  figures,  from  12.7  to  15.5,  and  to  0  ranging  from  3.5 
to  6.8 ;  that  higher  excess  losses,  6.7  to  14.3  per  cent,  are  found  both 
with  high  and  with  medium  C02,  16.0  and  12.9  per  cent,  with  low 
0,  2  and  4.1  per  cent,  and  with  low  C02,  10.4,  and  high  0,  9  per 
cent.  It  appears,  therefore,  that  the  lowest  losses  are  always  found 
within  the  narrow  range  of  3.5  to  say  7.5  per  cent  0,  while  both 
high  and  low  losses  may  be  found  with  C02  between  12.9  and  16.0 
per  cent. 

Tests  of  a  Mosher  Marine  Boiler. — On  page  612  are  the  principal 
results  of  four  tests  by  George  H.  Barrus  in  1910  of  one  of  the 
Mosher  boilers  built  for  the  U.  S.  battleships  Kearsarge  and  Ken- 
tucky. (See  Fig.  139,  page  372.)  The  tests  were  each  24  hours  long. 
The  fuel  was  semi-bituminous  coal : 

The  relatively  low  result  in  the  third  test  may  be  partly  accounted 
for  by  the  low  percentage  of  C02  and  the  high  percentage  of  0  in 
the  chimney  gases. 


612 


STEAM-BOILER  ECONOMY. 

TESTS    OF   A  MOSHER   MARINE   BOILER 


Coal  per  sq.ft.  grate  per  hr.,  Ibs  

15.2 

24.6 

34.8 

39.9 

Water  per  sq.ft.  heating  surface  per  hr.,  Ib 

3.7 

6.0 

7.9 

9.2 

Temperature  of  escaping  gases,  deg.  F.  .  . 

507 

568 

596 

625 

Equiv.  evap.  from  and  at  212°  per  Ib. 

comb.,  Ibs  

12.02 

11.69 

10.91 

11.22 

Efficiency  based  on  combustible,  %  

75.1 

72.7 

67.8 

69.7 

Efficiency  based  on  dry  coal,  %  

71  5 

70  0 

66  0 

67  6 

Gas  analysis,  Average: 

CO2  

12  4 

11  7 

10  6 

11  5 

O   % 

6  1 

7  05 

8  1 

7  o 

CO,  %.. 

0.4 

0  36 

0  4 

0  5 

Tests  of  the  "Wyoming"  Boiler.— The  results  of  six  tests  of  a  Bab- 
cock  &  Wilcox  marine  boiler  built  for  the  U.  S.  battleship  "Wyoming" 
are  reported  in  the  Journal  of  the  American  Society  of  Naval  En- 
gineers, Nov.,  1910.  They  correspond  closely  with  the  results  obtained 
with  the  "Cincinnati"  boiler  ten  years  earlier.  The  most  important 
figures  are  given  in  the  table  below: 

TESTS    OF    THE    " WYOMING"    BOILER. 


No.  of  test  

1 

2 

3 

4 

5 

6 

Duration,  hours  

24.06 
15.22 

3.88 
11.42 
12.15 

74.39 
0.07 
3.27 
11.09 
2.09 
9.08 
13.2 
4.2 
0.5 
18.41 
491 

24.5 
24.81 

6.43 
11.61 
12.07 

73.95 
0.06 
3.34 
12.24 
1.61 
8.80 
13.6 
4.7 
0.4 
18.07 
545 

24 
35.48 

9.03 

11.38 
11.77 

72.06 
0.06 
3.44 
14.63 
2.15 
7.66 
12.9 
4.5 
0.5 
18.80 
602 

24 
41.53 

10.52 
11.38 
11.89 

72.80 
0.09 
3.45 
14.20 
3.18 
6.28 
13.6 
3.9 
0.8 
17.54 
628 

3 
70.24 

14.76 
9.45 
10.33 

63.25 
0.07 
3.46 
16.31 
4.98 
11.93 
11.6 
5.07 
1.09 
19.40 
659 

6 
43.81 

10.52 
10.75 
11.30 

69.18 
0.07 
3.37 
16.59 
3.83 
6.96 
12.7 
3.0 
0.9 
18.46 
604 

Lbs.  coal  per  sq.ft.  of  grate  per  hr  
Equiv.  evap.  from  and  at  212°,  Ibs., 
per  sq  f  t  H  S  per  hr 

per  Ib  dry  coal 

per  Ib   combustible 

Heat  balance,  based  on  combustible: 
Efficiency  of  boiler   % 

Loss  due  to  moisture  in  coal  
Loss  due  to  hydrogen  in  coal  
Loss  in  dry  chimney  gases 

Loss  due  to  incomplete  combustion  .... 
Radiation  and  unaccounted  for  
Gas  analyses,  CO»  

O               

CO.               

Dry  gas  per  Ib.  carbon  
Temperature  of  escaping  gases,  deg.  F  .  .  . 

The  coal  was  semi-bituminous.,  volatile  matter  21%  of  the  com- 
bustible; moisture,  0.86;  ash,  3.61;  B.T.U.  per  Ib.  combustible, 
15,838. 

Tests  of  Large  Boilers  (2365  H.P.)  of  the  Delray  Station  of  the 
Detroit  Edison  Co.  (D.  S.  Jacobus,  Trans.  A.  S.  M.  E.,  1911).— The 
boilers  described  in  this  paper  are  of  the  Stirling  type,  modified'  as 


RESULTS  OF  STEAM-BOILER   TRIALS. 


613 


FIG.  257. — HALF  SECTIONS  OF  Two  BOILERS  OF  THE  DETROIT  EDISON  Co. 


614 


STEAM-BOILER  ECONOMY. 


shown  in  Fig.  257.  The  cut  shows  a  half  section  of  two  boilers,  one 
of  them  being  fitted  with  a  Roney  stoker  and  the  other  with  a  Taylor 
stoker.  The  boilers  are  remarkable  in  being  by  far  the  largest  that 
have  ever  been  built,  and  in  being  provided  with  furnaces  having 
vastly  larger  combustion-space  than  is  ordinarily  used.  The  results 
also  established  a  new  record  of  boiler  performance,  which  may  be 
used  as  a  standard  of  comparison  with  other  boiler  tests.  The  com- 
bined efficiency  of  boiler  and  grate,  based  on  dry  coal,  is  represented 
approximately  by  the  formula  E  =  80  — 1.33  (W/S  —  3)  and  the 
ten  best  out  of  the  sixteen  tests,  in  which  the  air  supply  was  most 
carefully  regulated  gave  an  efficiency  about  1  per  cent  higher.  The 
principal  results  are  given  in  the  following  tables.  The  coal  used  was 
West  Virginia  bituminous,  containing  about  35%  volatile  matter  in 
the  combustible  and  of  an  average  heating  value  of  about  15,250 
B.T.U.  per  Ib.  combustible,  except  in  three  of  the  tests,  Nos.  16,  17 
and  18,  in  which  the  volatile  matter  was  about  30%  and  the  B.T.U.  per 
pound  combustible  about  15,550. 

Each  boiler  is  rated  at  2365  H.P.  on  the  basis  of  10  sq.  ft.  of 
heating  surface  per  H.P.  and  is  designed  to  carry  a  steam  turbine 
load  of  6000  kw.  in  the  daytime  and  7000  or  8000  kw.  in  the  evening. 

PRINCIPAL   RESULTS   OF   DETROIT   EDISON    CO.'S   TESTS. 
Tests  with  Roney  Stoker. 


No.  of 
Teat. 

Length, 
Hours. 

Evap. 
per 
Sq.ft. 
H.  S. 
per  Hr., 
Lbs. 

Per  cent 
Rating. 

B.T.U. 
per  Lb. 
Coal. 

Percent 
Ash  in 
Dry 
Coal. 

Effici- 
ency 
Based 
on  Dry 
Coal. 

Effici- 
ency 
Based 
onCom- 
bustible 
tible.* 

Per  cent 
Steam 
used  by 
Stoker  f 

Per  cent 
Com- 
bustible 
in  Ash. 

Temp, 
of  Flue 
Gases 
Leaving 

1 
2 
3 
4 
5 
6 
16 
17 
18 

25 
24 
24 
30 
24 
24 
32 
16 
24 

3.63 
2.78 
3.92 
5.26 
3.24 
5.20 
3.40 
6.67 
6.75 

105.0 
80.0 
113.8 
152.4 
94.0 
150.7 
98.6 
193.3 
195.7 

14,362 
14,225 
14,308 
13,756 
13,896 
14,037 
14,476 
14,493 
13,689 

5.98 
6.52 
7.40 
6.54 
6.89 
6.13 
9.30 
8.24 
9.81 

77.84 
79.88 
77.45 
75.78 
81.15 
75.28 
80.98 
76.73 
75.57 

78.80 
80.84 
78.93 
77.48 
82.98 
76.65 
83.54 
78.37 
77.51 

0.63 
1.58 
1.75 
1.45 
1.34 
1.39 
1.32 

19.6 
17.9 
24.4 
30.8 
31.6 
26.7 
34.1 
24.6 
23.2 

576 
480 
542 
670 
483 
662 
460 
636 
694 

Tests  with  Taylor  Stoker. 


7 

24 

5.22 

151.2 

14,000 

7.03 

77.07 

78.92 

2.61 

31.5 

575 

8 

24 

3.72 

107.9 

13,965 

6.34 

80.28 

81.72 

2.44 

27.1 

493 

9 

50 

5.62 

162.8 

13,998 

6.75 

77.85 

79.38 

2.87 

31.3 

574 

10 

48 

3.22 

92.9 

14,188 

9.90 

77.90 

81.78 

2.63 

27.2 

487 

11 

26.5 

7.29 

211.3 

14,061 

9.55 

75.84 

77.71 

3.41 

36.1 

651 

12 

48 

4.18 

121.3 

14,010 

8.09 

79.24 

80.82 

2.57 

27.6 

535 

14 

24 

6.40 

185.5 

14,272 

8.71 

76.42 

78.60 

2.95 

28.8 

647 

*  Approximate;  calculated  from  the  efficiency  based  on  dry  coal  by  adding  80%  of  the  heat 
loss  due  to  carbon  in  ash,  taken  from  the  heat  balance. 

t  By  stoker  engines  and  steam  jets  in  the  Roney  tests  and  by  engines  driving  stokers  in 
•team  turbine  driving  fan  in  the  Taylor  tests. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


615 


HEAT   BALANCE,    PERCENTAGES   OF   TOTAL   HEAT  IN   COAL. 

Flue  Gas  Analyses  and  Temperature  Taken  in  Breeching. 
Roney  Stoker  Tests. 


No.  of 
Test. 

Absorbed 
Boifer. 

Moist- 
ure in 
Coal. 

Hydro- 
gen in 
Coal. 

Heat  to  Chimney 

Carbon 
Mon- 
oxide. 

Carbon 
in  Ash. 

Radia- 
tion, 
etc. 

Heat  to 
Chimney. 

Moist- 
ure in 
Air. 

Total. 

1 

77  .S4 

0.18 

4.55 

13.56 

0.37 

13.93 

0.23 

1.20 

2.07 

2 

79.88 

0.16 

4.36 

9.15 

0.26 

9.41 

0.42 

1.20 

4.57 

3 

77.45 

0.15 

4.48 

11.39 

0.32 

11.71 

0.74 

1.85 

3.62 

4 

75.78 

0.17 

4.49 

12.79 

0.36 

13.15 

1.95 

2.13 

2.33 

5 

81.15 

0.16 

4.29 

9.11 

0.20 

9.31 

1.29 

2.29 

1.51 

6 

75.28 

0.21 

4.74 

13.17 

0.36 

13.53 

1.16 

1.71 

3.37 

16 

80.98 

0.22 

4.18 

8.94 

0.19 

9.13 

0.27 

3.20 

2.02 

17 

76.73 

0.22 

4.47 

12.47 

0.28 

12.75 

0.74 

2.05 

3.04 

18 

75.57 

0.21 

4.64 

14.34 

0.27 

14.61 

0.62 

2.42 

1.93 

i 

Average 

2.72 

Taylor  Stoker  Tests. 

7 

77.07 

0.18 

4.58 

11.54 

0.28 

11.82 

1.61 

2.31 

2.43 

8 

80.28 

0.17 

4.28 

10.12 

0.24 

10.36 

0.40 

1.80 

2.71 

9 

77.85 

0.20 

4.31 

11.21 

0.25 

11.46 

0.44 

2.20 

3.54 

10 

77.90 

0.18 

4.34 

11.35 

0.26 

11.61 

0.27 

2.77 

2.93 

11 

75.84 

0.18 

4.47 

11.91 

0.35 

12.26 

0.59 

3.58 

3.08 

12 

79.24 

0.18 

4.46 

11.05 

0.21 

11.26 

0.16 

2.32 

2.38 

14 

76.42 

0.18 

4.51 

13.15 

0.27 

13.42 

0.31 

2.57 

2.59 

• 

Average 

2.81 

FLUE    GAS   ANALYSES. 

Roney  Stoker. 


No.  of 

Bottom  of  Last  Pass. 

Top  of  Last  Pass. 

In  Flue. 

Test. 

Test. 

CO,. 

O. 

CO. 

CO,. 

O. 

CO. 

CO,. 

O. 

CO. 

1 

13.22 

5.29 

0.00 

12.41 

6.48 

0.00 

11.95 

7.55 

0.05 

2 

15.18 

3.00 

0.06 

14.31 

4.01 

0.07 

14.33 

4.54 

0.11 

3 

14.50 

3.50 

0.09 

12.25 

6.12 

0.02 

13.05 

6.46 

0.18 

4 

14.45 

3.44 

0.35 

13.51 

4.68 

0.20 

14.74 

3.96 

0.54 

5 

15.65 

2.27 

0.25 

14.68 

3.40 

0.20 

14.40 

4.54 

0.35 

6 

14.77 

3.23 

0.20 

14.28 

3.87 

0.15 

14.66 

4.23 

0.31 

16 

13.82 

4.88 

0.00 

13.82 

•  4.88 

0.00 

13.55 

5.92 

0.07 

17 

14.25 

4.06 

0.40 

13.98 

4.48 

0.25 

14.69 

4.55 

0.20 

18 

14.16 

5.04 

0.16 

Taylor  Stokers. 


7 

15.46 

2.83 

0.08 

12.16 

6.64 

0.00 

14.00 

5.50 

0.42 

8 

15.04 

3.35 

0.02 

12.74 

5.83 

0.01 

13.69 

5.82 

0.10 

9 

15.84 

2.40 

0.03 

13.88 

4.62 

0.02 

14.74 

4.57 

0.12 

10 

13.14 

5.59 

0.00 

11.91 

6.96 

0.00 

11.86 

7.96 

0.06 

11 

15.25 

2.92 

0.25 

14.62 

3.30 

0.21 

15.45 

3.86 

0.17 

12 

14.83 

3.59 

0.00 

13.28 

5.35 

0.00 

13.79 

5.73 

0.04 

13 

15.43 

2.96 

0.09 

13.85 

4.65 

0.37 

15.17 

3.90 

0.19 

14 

15.07 

3.33 

0.17 

12.90 

5.67 

0.06 

14.20 

5.08 

0.08 

15 

11.70 

7.16 

0.12 

10.35 

8.79 

0.01 

10.83 

8.93 

0.09 

616 


STEAM-BOILER  ECONOMY. 


Some  data  not  included  in  the  tables  are :  Grate  surface,  measured 
from  the  front  of  the  furnace  to  the  rear  of  the  dumping  grates, 
Koney  stoker,  446  sq.  ft.,  Taylor  stoker,  405  sq.  ft.  Steam  pressure, 
by  gauge,  192  to  207  Ibs.  Superheat  102°  to  168°.  Horse  power 
developed  1903  to  5083. 

The  relation  of  the  efficiency  of  boiler  and  grate  to  the  rate  of 
driving  is  plotted  in  Fig.  258.  Ten  of  the  best  tests  come  very  near 


tss 
81 
^80 
§79 

ITS 

76 

75 

w 

_ 

-^i 

RR 

xs 

T 

02 

R 

^=5» 

^ 

T 

XL 

-IF 

—  «-^ 

^~- 

--^ 

^ 

97 

^3 

R 

7T 

"~~~ 

7R 

" 

^ 

^^ 

4R 

i 

"r> 

^ 

^ 

-v^ 

R 

3= 

18  K 

11T 

33                       4                       5                       6                       7 

Rate  of  Driving 
FIG.  258. — RESULTS  OF  THE  DETROIT  TESTS  j 

to  the  straight  line  whose  equation  is  81  — 1.33  (W/S  —  3)  and 
the  other  six  fall  considerably  below  the  line.  The  difference  between 
the  efficiency  obtained  in  each  test  and  that  calculated  from  this 
formula  is  given  in  the  table  below : 

TEN   BEST   RESULTS. 

(R,  Roney;  T,  Taylor.) 


No.  of  Test 

5R 

1QR 

8T 

\2T 

IT 

9T 

14T 

1  1772 

18R 

11T 

W/S  
E  by  formula  
E  by  test  
Difference  

3.24 
80.68 
81.15 
+0.47 

3.40 
80.47 
80.98 
+0.51 

3.72 
80.04 
80.28 
+0.24 

4.18 
79.43 
79.24 
-0.19 

5.22 

78.04 
77.07 
-0.97 

5.62 
77.56 
77.85 
+0.29 

6.40 
76.47 
76.42 
—0.05 

6.67 
76.11 
76.73 
+0.62 

6.75 
76.00 
75.57 
-0.43 

7.29 

75.28 
75.84 
+0.56 

SIX    LOWER    RESULTS. 


No.  of  Test. 

2R 

WT 

IR 

3R 

6fl 

4R 

W/S  

2.78 

3.22 

3.63 

3.92 

5.20 

5.26 

E  by  formula  

81.29 

80.71 

80.16 

79.77 

78.07 

77.99 

E  by  test  
Difference  

79.88 
-1.41 

77.90 
-2.81 

77.84 
-2.32 

77.45 
-2.32 

75.28 
-2.79 

75.78 
-2.21 

The  lower  results  may  be  accounted  for  by  too  great  or  too  little 
air  supply,  as  shown  by  the  oxygen  in  the  flue  gases.  The  ten  high 
results  were  obtained  with  0  from  3.86  to  5.82%.  Of  the  six  low 
results  three  were  obtained  with  high  0,  6.46  to  7.96,  and  three  with 


RESULTS  OF  STEAM-BOILER   TRIALS. 


617 


low  0,  3.96  to  4.54.  To  obtain  the  highest  efficiency  it  appears  that 
0  must  be  below  6,  but  if  it  is  below  4.5  the  efficiency  may  be  low  on 
account  of  imperfect  combustion. 

The  reasons  for  the  high  efficiency  obtained  in  the  Detroit  tests  as 
compared  with  all  previous  tests  are :  1.  The  great  size  of  the  boiler, 
diminishing  the  radiation  loss.  2.  The  use  of  mechanical  stokers,  in- 
suring uniform  feeding  of  the  coal  and  the  avoidance  of  loss  of  heat 
from  the  opening  of  fire-doors.  .3.  The  enormous  size  of  the  combus- 
tion space,  making  possible,  with  proper  regulation  of  the  thickness  of 
coal  bed  and  of  the  air-supply,  the  complete  burning  of  the  volatile 


2          3  4  5  6          7  8  9          10         11          12         13         14 

Lbs.  Water  Evaporated  from  and  at  212  per  Sq.Ft.  Heating  Surface  per  Hour 

FIG.  259. — RELATION  OF  EFFICIENCY  TO  RATE  OF  DRIVING. 

gases  before  they  reach  the  heating  surface.  4.  The  great  care  given 
to  the  regulation  of  the  air-supply,  in  accordance  with  the  indications 
of  gas  analyses. 

The  greatest  source  of  probable  error  in  the  results  is  in  the 
sampling  and  analyses  of  the  coal.  The  sampling  and  the  analyses 
were  done  by  two  laboratories  and  their  results  averaged.  Individual 
analyses  showed  some  erratic  variations,  indicating  that  the  average 
analysis  may  have  an  error  of  1  per  cent,  and  that  the  error  in  some 
of  the  tests  may  have  been  as  high  as  2  per  cent. 

Comparison  of  Three  High  Records. — In  Fig.  259,  the  results  of  the 
Detroit,  the  Cincinnati,  and  the  Wyoming  tests  are  plotted  together 
with  the  curve  of  the  theoretical  maximum  efficiency  obtained  with 
Pittsburgh  coal,  with  20  per  cent  excess  air  supply  as  calculated  by 
formula  18  of  Chapter  IX.  The  Detroit  tests  approach  so  near  to  this 
theoretical  maximum  that  it  is  evident  that  but  little  margin  remains 
for  improving  the  efficiency  of  properly  built  and  properly  managed 


• 


618 


STEAM-BOILER  ECONOMY. 


boilers  and  furnaces,  except  such  as  may  be  made  by  the  use  of 
economizers.  The  difference  between  the  Wyoming  and  Cincinnati 
tests  and  the  theoretical  maximum  are  accounted  for  by  the  irregular- 
ities due  to  hand-firing,  and  to  the  restricted  volume  of  the  combustion 
chamber,  which  was  insufficient  for  complete  burning  of  the  gases.  A 
large  part  of  the  unaccounted-for  loss  in  the  heat  balance  was  un- 
doubtedly due  to  the  escape  of  unburned  hydrocarbons. 

In  Fig.  259,  the  efficiencies  plotted  are  all  based  on  combustible. 
Those  -of  the  Detroit  tests  are  represented  by  the  formula  E  =  82 — 
1.33  (W/S  —  3),  and  those  of  the  Wyoming  and  Cincinnati  tests  by 
E  =  79.5  —  1.4.  (W/S  —  3) .  The  following  table  shows  the  variation 
of  the  actual  efficiencies  from  those  computed  by  the  two  formulae : 


DETROIT        TESTS,    RONEY    STOKER. 


Rate  of  driving,  W/S  .... 
Efficiency,  actual  

2.78 

80.84 

3.24 

82.98 

3.40 
83.54 

3.63 

78.80 

3.92 

78.93 

5.20 
76.65 

5.26 

77.48 

6.67 
78.37 

6.75 
77.51 

from  formula.  . 
Difference  .  . 

82.29 
-1.45 

81.68 
+  1.30 

81.47 
+2.07 

81.16 
-2.36 

80.77 
-1.85 

79.07 
-2.42 

78.99 
-1.51 

77.11 
+  1.26 

77.00 
+0.51 

W/S 

Efficiency,  actual 

from  formula. 
Difference .  . 


'DETROIT"  TESTS,  TAYLOR  STOKER. 

3.22          3.72  4.18 

81.78        81.72        80.82 
81.71        81.04         80.43 


+0.07 


+0.68 


+0.39 


5.22 
78.92 
79.04 
-0.12 


5.62 
79.38 
78.51 


+0.87 


6.40 
78.60 
77.47 
+1.13 


7.29 
77.71 
76.28 
+1.43 


"CINCINNATI"  TESTS. 


W/S 

Efficiency,  actual 

from  formula. . 
Difference .  . 


5.18 
74.80 
76.45 
-1.65 

5.57 
77.90 
75.90 
+2.00 

8.42 
70.46 
71.91 
-1.51 

8.75 
70.60 
71.45 
-0.85 

9.58 
68.20 
70.21 
-2.01 

10.07 
70.10 
69.60 
+0.50 

13.67 
64.50 
65.63 
-1.13 

WYOMING       TESTS. 


w/s  

3.88 

6.43 

9.03 

10.52 

10.52 

14.76 

Efficiency,  actual. 

74.39 

73.95 

72.06 

72.80 

69.18 

63.25 

from  formula.  . 
Difference  

78.37 
-3.98 

74.70 
-0.75 

71.06 
+  1.00 

68.97 
+3.83 

68.97 
+0.21 

63.04 
+0.21 

Tests,  of  a  Locomotive. — W.  F.  M.  Goss,  in  Bulletin  402  of  the 
U.  S.  Geological  Survey,  1909,  describes  a  series  of  18  tests  made  at 
the  locomotive-testing  laboratory  of  Purdee  University  to  determine 
the  efficiency  of  a  locomotive  with  two  kinds  of  coal  at  different  rates 
of  driving.  The  boiler  had  111  2-inch  and  16  5-inch  tubes;  heating 
surface,  fire-box,  126  sq.  ft.,  water  side  of  tubes,  897  sq.  ft.,  outside 
of  superheater  tubes,  193  sq.  ft. ,  total  1216  sq.  ft.;  grate  surface  17.7 
sq.  ft.  The  two  coals  were:  A,  a  bituminous,  with  moisture  1.89%, 
ash  8.46%,  and  35.6%  volatile  matter  in  the  combustible,  and  B, 
semi-bituminous,  moisture  3.10%,  ash  8.92%,  volatile  17.1%.  Heat- 
ing value  per  pound  of  combustible,  A,  15,372;  B,  15,802  B.T.U.  per 
Ib.  The  principal  results  are  given  in  the  table  on  page  620.  Fig.  260 
shows  a  plotting  of  the  efficiency  based  on  combustible  consumed,  which 


RESULTS  OF  STEAM-BOILER   TRIALS. 


C19 


is  figured  by  subtracting  from  the  combustible  fired  (that  is  the  coal 
less  the  moisture  and  ash  determined  by  analysis)  the  combustible  in 
the  ash  an  refuse  from  the  grate  and  in  the  stack  and  flue  cinders. 
This  efficiency  is  very  much  higher  than  the  efficiency  of  the  boiler 
and  grate,  based  on  the  combustible  fired,  on  account  of  the  large 
loss  of  fuel  in  the  cinders.  The  most  notable  result  of  this  series  of 
tests  is  the  great  falling  off.  in  efficiency  and  the  large  "unaccounted 
for  loss"  in  the  case  of  the  semi-bituminous  coal.  The  report  says : 


""---, 

.  

Ph 

<«eo 

pofl, 

-^ 

SHin, 

3^ 

J&itn 

<^ 

^ 

^in 

•O.^ 

^00 

^jgjgj 

"^ 

"*"*•>•.», 

\ 

a 

\ 

%^ 

\ 

fe 

S** 

5 

X 

^. 

"0 

6         7         8         9        10        11       12        13 

FIG.  260. — RESULTS  OF  LOCOMOTIVE  TESTS. 

"The  cinders  from  coal  B  have  more  than  double  the  weight  and  each 
pound  has  nearly  double  the  heating  value  of  those  from  coal  A,  a 
result  doubtless  due  in  part  to  the  large  percentage  of  fine  material  in 
coal  B,  and  to  the  absence  of  such  material  in  coal  A." 

AVERAGED  HEAT  BALANCE  FOR  LOCOMOTIVE  TEST. 

(Percentages  of  total  heat  available.) 

Absorbed  by  the  water  in  the  boiler ^ 52 

Absorbed  by  the  steam  in  the  superheater 5 

Absorbed  by  steam  in  the  boiler  and  superheater 57 

Lost  in  vaporizing  moisture  in  the  coal 5 

Lost  through  the  discharge  of  CO 1 

Lost  through  the  high  temperature  of  escaping  gases,  the  products  of 

combustion 14 

Lost  through  unconsumed  fuel  in  the  form  of  front-end  cinders , 3 

Lost  through  unconsumed  fuel  in  the  form  of  cinders  or  sparks  passed 

out  of  the  stack 9 

Lost  through  unconsumed  fuel  in  the  ash 4 

Lost  through  radiation,  leakage  of  steam  and  water,  etc 7 


100 


620 


STEAM-BOILER  ECONOMY. 


RESULTS    OF    LOCOMOTIVE    TESTS. 


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11.47 

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7.02 

10.06 

11.70 

69.0 

73.45 

12.47 

6.11 

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19.75 

670 

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1.50 

134 

13.30 

7.10 

10.30 

46.7 

60.92 

12.05 

6.34 

.27 

20.41 

782 

14* 

1.50 

131 

12.77 

6.98 

10.33 

47.4 

61.74 

11.82 

6.77 

.16 

21.01 

772 

15* 

2.00 

89 

9.90 

7.95 

11.27 

53.6 

67.21 

11.57 

7.15 

.15 

21.43 

702 

16* 

2.50 

74 

9.33 

8.96 

11.56 

60.0 

69.79 

11.99 

7.43 

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20.92 

692 

17 

2.50 

58 

8.25 

10.16 

11.87 

69.7 

73.77 

12.20 

6.15 

.19 

20.31 

676 

18* 

2.50 

36 

5.12 

10.23 

12.38 

68.1 

74.64 

10.81 

8.82 

.11 

22.96 

579 

HEAT   BALANCE    (BASED    ON   COMBUSTIBLE    FIRED). 


Percentage  of  Heat. 

Ab- 

No. of 
Test. 

sorbed 
by 
Boiler 
and 
Super- 

Due to 
H20in 
Coal. 

Due  to 
H2O  in 
Air. 

Due  to 
H20 
Formed 
by  Hin 
Coal. 

Due  to 
Escap- 
ing 
Gases. 

Due  to 
Incom- 
plete 
Com- 
bustion. 

Due  to 
Front 
End 
Cinders. 

Due  to 
Stack 
Cinders. 

Due  to 
Refuse 
in  Ash 
Pan. 

Unac- 
counted 
for. 

heater. 

1 

58.75 

0.16 

0.46 

4.11 

12.83 

3.74 

8.02 

0.92 

4.15 

6.86 

2 

59.28 

.15 

.20 

4.05 

13.35 

3.67 

7.94 

.95 

3.48 

6.93 

3 

60.08 

.16 

.53 

4.11 

13.31 

2.93 

5.75 

.89 

6.06 

6.17 

4 

66.37 

.27 

.25 

4.48 

13.58 

.47 

2.81 

1.34 

4.13 

6.30 

5 

63.16 

.18 

.40 

4.17 

14.93 

1.56 

5.90 

1.11 

3.78 

4.81 

6* 

53.90 

.22 

.35 

3.45 

13.32 

.42 

11.96 

1.80 

5.23 

9.37 

7 

61.34 

.19 

.49 

4.41 

12.86 

4.90 

4.95 

1.35 

5.88 

4.63 

8 

62.34 

.15 

.31 

4.16 

14.98 

1.09 

4.08 

.81 

5.12 

6.96 

9* 

65.70 

.35 

.37 

3.41 

15.07 

.05 

4.22 

1.53 

4.65 

4.65 

10 

66.16 

.16 

.27 

4.24 

15.18 

1.27 

3.64 

.73 

3.70 

4.65 

11 

66.25 

.22 

.27 

4.21 

14.79 

1.49 

3.02 

1.33 

3.93 

4.49 

12 

69.12 

.18 

.37 

3.80 

14.11 

1.27 

1.16 

.99 

3.74 

5.26 

13* 

46.72 

.28 

.35 

3.51 

13.98 

1.26 

16.74 

3.76 

2.81 

10.59 

14* 

47.45 

.34 

.28 

3.61 

14.46 

.78 

15.10 

5.20 

2.84 

9.94 

15* 

53.67 

.27 

.27 

3.46 

13.78 

.73 

12.09 

2.06 

6.00 

7.67 

16* 

59.97 

.26 

.27 

3.42 

14.56 

.19 

7.82 

2.03 

4.22 

7.26 

17 

69.73 

.22 

.38 

3.89 

14.58 

.85 

1.76 

.86 

2.86 

4.87 

18* 

68.14 

.35 

.29 

3.06 

13.58 

.56 

2.52 

1.10 

5.09 

5.31 

*  Semi-bituminous  coal. 


RESULTS  OF  STEAM-BOILER   TRIALS.  621 

Following  is  an  extract  from  the  general  conclusions  of  the  report : 

There  were  in  1906,  on  the  railroads  of  the  United  States,  51,000 
locomotives.  It  is  estimated  that  these  locomotives  consumed  during 
the  year  not  less  than  90,000,000  tons  of  fuel,  which  is  more  than  one- 
fifth  of  all  the  coal,  anthracite  and  bituminous,  mined  in  the  country 
during  the  same  period.  The  coal  thus  used  cost  the  railroads  $170,- 
500,000.*  That  wastes  occur  in  the  use  of  fuel  in  locomotive  service  is 
a  matter  which  is  well  understood  by  all  who  have  given  serious  atten- 
tion to  the  subject,  and  the  tests  whose  results  are  here  presented 
show  some  of  the  chan»els  through  which  these  wastes  occur.  These 
results  are  perhaps  more  favorable  to  economy  than  those  attained  by 
the  average  locomotive  of  the  country,  as  the  coal  used  in  the  tests 
was  of  superior  quality,  the  type  of  locomotive  employed  was  better 
than  the  average,  and  the  standards  observed  in  the  maintenance  of 
the  locomotive  were  more  exacting.  But  so  far  as  they  apply,  the 
results  may  be  accepted  as  fairly  representative  of  general  locomotive 
practice.  They  apply,  however,  only  when  the  locomotive  is  running 
under  constant  conditions  of  operation.  They  do  not  include  the  inci- 
dental expenditures  of  fuel  which  are  involved  in  the  starting  of  fires, 
in  the  switching  of  engines,  and  in  the  maintenance  of  steam  pressure 
while  the  locomotive  is  standing,  nor  do  they  include  a  measure  of  the 
heat  losses  occasioned  by  the  discharge  of  steam  through  the  safety 
valve.  Observations  on  several  representative  railroads  have  indicated 
that  not  less  than  20  per  cent  of  the  total  fuel  supplied  to  locomotives 
performs  no*  function  in  moving  trains  forward.  It  disappears  in  the 
incidental  ways  just  mentioned  or  remains  in  the  fire  box  at  the  end 
of  the  run.  The  fuel  consumption  accounted  for  by  the  heat  balance 
is,  therefore,  but  80  per  cent  of  the  total  consumed  by  the  average  loco- 
motive in  service.  Applied  on  this  basis  to  the  total  consumption  of 
coal  for  the  country,  the  heat  balance  may  be  converted  into  terms  of 
tons  of  coal  as  follows : 

SUMMARY   OF  RESULTS   OBTAINED   FROM   FUEL   BURNED   IN   LOCOMOTIVES. 

1.  Consumed  in  starting  fires,  in  moving  the  locomotive  to  its  train,  in       Tons. 

backing  trains  into  or  out  of  sidings,  in  making  good  safety-valve 
and  leakage  losses,  and  in  keeping  the  locomotive  hot  while 
standing  (estimated) 18,000,000 

2.  Utilized,  that  is,  represented  by  heat  transmitted  to  water  to  be 

vaporized 41,040,000 

3.  Required  to  evaporate  moisture  contained  by  the  coal 3,600,000 

4.  Lost  through  incomplete  combustion  of  gases 720,000 

5.  Lost  through  heat  of  gases  discharged  from  stack 10,080,000 

6.  Lost  through  cinders  and  sparks 8,640,000 

7.  Lost  through  unconsumed  fuel  in  the  ash 2,880,000 

8.  Lost  through  radiation,  leakage  of  steam  and  water,  etc  : , . .  5,040,000 

90,000,000 
*  Kept.  Interstate  Commerce  Commission,  1906. 


622 


STEAM-BOILER  ECONOMY. 


It  is  apparent  from  this  exhibit  that  the  utilization  of  fuel  in 
locomotive  service  is  a  problem  of  large  proportions,  and  that  if  even 
a  small  saving  could  be  made  by  all  or  a  large  proportion  of  the  locomo- 
tives of  the  country  it  would  constitute  an  important  factor  in  the  con- 
servation of  the  nation's  fuel  supply. 

Application  of  the  Criterion  Formula  for  ^    to  the  ''Cincinnati," 
"Wyoming,"  Detroit  and  Locomotive  Tests. — On  page  319  will  be 
found  tables  giving  the  values  of  a^    for  these  tests,  computed  'from 
formula  (18)  page  316.     Fig.  261  is  a  plotting  of  these  values. 


150 
140 


KM) 
150 


2  3          4  5  6  7  8  9          10         11         12         13         14 

^/g  =P>s.  water  evaporated  from  and  at  212°per  sq.ft.heating  surface  per  hour. 

FIG.  261. — VALUES  OF  THE  COEFFICIENT  en. 

The  average  value  of  a\  for  the  47  tests  is  211.  Omitting  four  high 
values,  above  270,  the  average  is  201.  The  figures  in  the  table  and 
the  chart  plotted  from  do  not  indicate  that  there  is  any  definite  rela- 
tion between  the  value  of  a\  and  either  the  type  of  the  boiler  or  the 
rate  of  driving.  The  four  exceptionally  high  figures,  above  270,  are 
found  at  rates  of  driving  ranging  from  2.78  to  9.58,  and  the  eight 
lowest  figures,  below  170,  are  found  at  rates  of  driving  from  3.22  to 
14.76.  Of  the  47  tests,  42  give  values  of  ai  between  150  and  270, 
averaging  202,  and  37  give  values  between  160  and  260,  averaging  206. 

The  large  range  of  variation  appears  to  be  due  to  errors  of  measure- 
ment of  the  coal  or  water,  or  of  sampling  and  analysis  of  the  coal  and 


RESULTS  OF  STEAM-BOILER   TRIALS. 


623 


the  flue  gases.  The  conclusion  drawn  from  this  investigation  is  that 
with  any  form  of  boiler  and  with  any  rate  of  driving,  the  average 
value  of  the  coefficient  a  is  about  200,  provided  the  efficiency  is  not 
reduced  by  excessive  radiation,  leaks  of  air  into  the  setting,  short- 
circuiting  of  the  gases,  or  foulness  of  the  heating  surface  from  scale  or 
soot,  and  that  if  in  any  test  these  causes  of  high  values  of  a\  are 
avoided,  and  the  computation  shows  a  value  of  a  below  150  or  above 
250,  errors  in  measurement,  sampling  or  analysis  are  the  probable 
cause  of  the  variation. 

Range  of  Results  Obtained  from  Anthracite  Coal, — Selecting  the 


12.8F.  per  Ib.  Combustible. 

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2.                      3                      4-                       5                      6                      7                       § 

Lbs.Water  Evaporated  per  sq.ft.  of  Hearing  Surface  per  Hour. 

FIG.  262.  —  RESULTS  OF  TESTS  WITH  ANTHRACITE  COAL, 

highest  results  obtained  at  different  rates  of  driving  with  anthracite 
coal  in  the  Centennial  tests  in  1876,*  and  the  highest  results  with 
anthracite  reported  by  Mr.  Barrus  in  his  book  on  Boiler  Tests,  the 
two  curves  in  the  diagram,  Fig.  262,  have  been  plotted,  showing  the 
maximum  results  which  may  be  expected  with  anthracite  coal,  the 


*  Reports  and  Awards  Group  XX,  International  Exhibition,  Phila.,  1876; 
also  Clark  on  the  Steam-engine,  vol.  i.  p.  253. 


624  STEAM-BOILER  ECONOMY. 

first  under  exceptional  conditions,  such  as  obtained  in  the  Centennial 
tests,  and  the  second  under  the  best  conditions  of  ordinary  practice 
(Trans.  Am.  S.oc.  M.  E.,  vol.  xviii.  p.  354).  From  these  curves  the 
following  figures  are  obtained: 

Lbs.  water  evaporated  from  and  at  212°  per  sq.  ft.  heating  surface  per  hour: 

2          2.5          3         3.5         4          4.5          5  678 

Lbs.  water  evaporated  from  and  at  212°  per  Ib.  combustible: 

Centennial. ...  12.         12.1       12.1       12.       11.85     11.7       11.45     10.8  9.8  8.5 

Barrus 11.65     11.65     11.55     11.4     11.2       10.95     10.6        9.9  9.2  8.5 

Avg.  Cent'l. .  .12.0       11.6       11.2       10.8     10.4       10.0        9.6        8.8  8.0  7.2 

The  figures  in  the  last  line  are  taken  from  a  straight  line  drawn  as 
nearly  as  possible  through  the  average  of  the  plotting  of  all  the  Cen- 
tennial tests.  The  poorest  results  are  far  below  these  figures.  It  is 
evident  that  no  formula  can  be  constructed  that  will  express  the 
relation  of  economy  to  rate  of  driving  as  well  as  do  the  three  lines 
of  figures  given  above.  The  great  width  of  the  field  between  the  high- 
est and  lowest  curves  on  the  diagram  is  an  indication  of  the  great 
saving  of  fuel  that  may  be  made  by  bringing  poor  boiler  performance 
up  to  the  level  of  the  best. 

Tests  with  Anthracite  at  the  Centennial  Exhibition,  1876, — The 
table  on  page  625  gives  the  principal  results  obtained  in  the  economy 
trials  at  the  Centennial  Exhibition,  together  with  the  capacity  and 
economy  figures  of  the  capacity  trials  for  comparison,  and  the  results 
are  plotted  on  the  diagram,  Fig.  262.  Some  of  the  results  are  also 
plotted  on  the  diagram,  Fig.  77,  page  299,  for  comparison  with  theo- 
retical performance  under  certain  assumed  conditions.  Of  the  four- 
teen boilers  tested,  illustrations  of  seven  have  already  been  given,  as 
follows:  Root,  page  363,  Firmenich,  page  359;  Babcock  &  Wilcox, 
page  361;  Galloway,  page  343;  Wiegand  page  354;  Kelly,  page  355; 
Rogers  and  Black,  page  357.  The  Root  boiler  used  in  the  test  differed 
from  the  one  on  page  363  in  not  having  the  series  of  horizontal  longi- 
tudinal steam-  and  water-drums,  a  single  transverse  drum  being  used 
instead.  The  other  seven  boilers  are  illustrated  and  briefly  described 
below. 

The  Lowe  boiler,  Fig.  263,  is  an  ordinary  cylindrical  tubular  boiler 
4  X  ISi  ft.  with  forty-six  tubes  3  ins.  X  15  ft,,  with  a  chamber  or 
connection  in  the  front  end  of  the  boiler,  the  rear  of  which  forms 
the  front  tube-sheet.  The  bridge-wall  back  of  the  grate  is  extended 


RESULTS  OF  STEAM-BOILER    TRIALS. 


625 


up  to  the  shell.    The  heated  gases  pass  through  side  openings  through 

the  water -space  into  the  front 

chamber,    thence    through   the 

tubes  to  the  rear  of  the  boiler, 

then     through     a     return-flue 

along  the  lower  half  of  the  shell 

to  the  rear  of  the  bridge-wall, 

when  they  rise  through  two  side 

flues,   and   circulating   around 

the  upper  half  of  the  shell  and 

a  superheating  drum,  escape  to 

the  uptake. 


FIG.  263, — THE  LOWE  BOILER. 


Economy  Tests. 

Capacity  Tests. 

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p.ct. 

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H.P. 

H.  P. 

Ibs. 

Ibs. 

Root 

34  6 

9  1 

10  4 

2  59 

12  .  094 

393 

41.4 

119.8 

148  6 

10.441 

3.21 

Firmenich  

64.3 

12.0 

10.4 

li93 

11.988 

415 

32.6 

57.8 

68.4 

11.064 

2.29 

Lowe 

30  6 

6  8 

11.3 

2  15 

11.923 

333 

9.4 

47.0 

69  3 

11.163 

3  17 

Smith  

45.8 

12.1 

11.1 

2^79 

11.906 

411 

iis 

99.8 

125.0 

11.925 

3.74 

Babcock  &  Wilcox 

37.7 

10.0 

11.0 

2.79 

11.822 

296 

2.7 

135.6 

186.6 

10.330 

3.84 

Galloway  

23.7 

9.6 

11.1 

4.18 

11.583 

303 

i!i 

103.3 

133.8 

11.216 

5.41 

do  semi-bit,  coal 

23.7 

7.9 

8.8 

3.68 

12.125 

325 

0.3 

90.9 

125.1 

11.609 

5.06 

Andrews  

15.6 

8.0 

10.3 

2  67 

11.039 

420 

7l!7 

42.6 

58.7 

9.745 

4.00 

Harrison  

27.3 

12.4 

8.5 

3.16 

10.930 

517 

O.Q 

82.4 

108.4 

9.889 

4.15 

Wiegand 

30.7 

12  3 

9  5 

3  80 

10.834 

524 

20  5 

147  5 

162  8 

9.145 

4.19 

Anderson  

17.5 

9.7 

9.3 

3^03 

10.618 

417 

15i7 

98^0 

132!8 

9.568 

4.11 

Kelly 

20.9 

10.8 

9.0 

4.40 

10.312 

5.6 

81.0 

99.9 

8  397 

5.43 

Exeter  

33.5 

9.3 

11.4 

1.59 

10.041 

430 

4.2 

72.1 

108.0 

9.974 

2.38 

Pierce 

14.0 

8  0 

11  0 

5.11 

10  021 

374 

5  2 

51  7 

67  8 

9  865 

6.70 

Rogers  &  Black  .  . 

19.0 

8.6 

9.9 

3.94 

9.613 

572 

2.1 

45.7 

67.2 

9.429 

5.80 

Averages  

•• 

3.19 

11.123 

85.0 

110.8 

10.251 

4.23 

The  Smith  boiler,  Fig.  264,  is  an  ordinary  return-tubular  boiler, 
supplied  with  additional  heating  surface  in  the  setting.  From  the 
hollow  cast-iron  bridge-wall  a  number  of  pipes  run  horizontally  under 
and  back  of  the  boiler  and  connect  to  short  vertical  tubes  screwed  into 
a  larger  horizontal  pipe  located  back  of  the  shell  and  connected  thereto. 
In  addition  to  the  above,  two  cast-iron  pipes  run  along  either  side  of 
and  below  the  grate  and  are  connected  with  the  water-space  in  the 
shell.  In  the  latter  are  attached  on  either  side  a  series  of  vertical 
conical  castings,  bulb-shaped  at  their  tops,  with  a  small  wrought- 
iron  pipe  in  each  as  an  outlet  for  steam,  and  the  several  small  steam- 
pipes  are  connected  together  and  to  the  steam-space  of  the  main  shell. 


626 


STEAM-BOILER  ECONOMY. 


The  Andrews  boiler,  Fig.  265,  is  of  the  double  marine  tubular  type 
with  internal  furnace  and  external  sheet-iron  connections  for  direct- 
ing the  products  of  combustion  from  the  lower  set  of  tubes  to  the 
upper.  The  shell  is  rectangular  with  a  semi-cylindrical  top. 


FIG  264. — THE  SMITH  BOILER. 


The  Harrison  boiler,  Fig.  266,  consists  of  sections  of  hollow  cast- 
iron  spheres,  8  ins.  diameter,  with  curved  necks,  cast  in  groups  of 
two  and  four  and  held  together  by  bolts  extending  through  the  spheres 
and  necks  the  entire  length  of  the  sections.  The  sections  are  set 
side  by  side  at  the  angle  shown. 


0000 
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V 


FIG.  265. — THE  ANDREWS  BOILER. 


FIG.  266. — THE  HARRISON 
BOILER. 


The  Anderson  boiler,  Fig.  267,  is  composed  of  sections,  each  con- 
taining nine  wrought-iron  tubes  3  ins.  diameter  and  10  ft.  long, 
which  are  nearly  horizontal  and  arranged  in  a  vertical  row.  The  four 
lower  tubes  are  secured  at  their  front  ends  to  a  cast-iron  chamber 
and  rise  a  little  from  front  to  rear.  The  front  ends  of  the  five  upper 
tubes  are  similarly  attached  to  an  upper  chamber,  and  slope  a  little 


RESULTS   OF  STEAM-BOILER   TRIALS. 


627 


from  front  to  rear.  The  rear  ends  of  all  the  tubes  are  united  by  a 
manifold.  The  lower  front  chambers  are  connected  at  their  lower 
ends  and  the  upper  front  chambers  at  their  upper  ends.  A  horizontal 
partition  is  placed  above  the  four  lower  tubes,  so  as  to  compel  the 


FIG.  267. — THE  ANDERSON  BOILER.         FIG.  268.— THE  EXETER  BOILER. 

gases  to  flow  first  along  the  four  lower  tubes  and  then  along  the  five 
upper  tubes. 

The  Exeter  boiler,  Fig.  268,  consists  of  hollow,  rectangular,  cast- 
iron,  slab-shaped  sections  set  transversely,  with  twelve  oblong  openings 
in  two  horizontal  flues  through  each  section.  Twenty-seven  such 
sections  are  placed  one  in  the  rear  of  the  other  and  connected  through 
short  side  pipes  to  one  steam-  and  one  feed-pipe  thus  forming  a  com- 
plete boiler.  Two  of  these  boilers  are  placed  side  by  side  over  one 
grate.  The  gases  from  the 
grate  pass  to  the  rear  of 
the  boiler  through  the 
lower  row  of  passages  and 
return  through  the  upper 
rows. 

The  Pierce  boiler,  Fig. 
269,  consists  of  a  flat-end- 
ed cylinder  directly  above 
the  fire-grate,  revolving 
on  trunnions.  The  heat- 
ed gases  envelop  the 
cylinder  and  enter  one 
end  of  an  annular  row 
of  tubes  in  the  shell,  and 
after  passing  through 
them  return  through 
another  row  of  tubes  concentric  with  the  first  and  thence  escape  to  the 
chimney.  Cups  are  secured  around  the  tubes  of  the  outer  row,  to  catch 
the  water  whenever  the  tube  is  lifted  above  the  water-line  by  the 
revolving  of  the  shell,  and  thus  prevent  overheating  of  these  tubes  and 


FIG.  269. — THE  PIERCE  BOILER. 


628  STEAM-BOILER  ECONOMY. 

of  the  shell.    The  feed-water  is  introduced  through  one  trunnion  and 
steam  is  taken  out  through  the  other. 

Some  of  the  conclusions  which  may  be  drawn  from  the  results  of 
the  Centennial  tests  are  the  following : 

1.  The  high  results  obtained  by  the  first  six  boilers  on  the  list, 
page  625,  viz. :  the  Boot,  Firmenich,  Lowe,  Smith,  .Babcock  &  Wilcox, 
and  Galloway  boilers,  constitute  a  standard  of  performance  which  has 
not  been  excelled  since  1876  in  any  properly  authenticated  series  of 
tests  with  anthracite  coal. 

2.  These  high  figures  being  obtained  with  boilers  of  widely  different 
types,  it  is  evident  that  economy  of  fuel  does  not  depend  to  any  great 
extent  on  the  type  of  boiler. 

3.  The  low  results  obtained  in  the  tests  of  all  the  other  boilers  are 
not  explained  by  their  design,  or  by  anything  in  the  record  of  their 
tests.     Of  the  possible  causes  of  low  performance  are  excessive  air- 
supply,  especially  at  the  higher  rates  of  driving;  short-circuiting  of 
the  gases;  excessive  loss  by  radiation.     The  lack  of  analyses  of  the 
chimney-gases  prevents  the  drawing  of  any  definite  conclusions   in 
regard  to  the  air-supply. 

4.  The  most  important  conclusion  is  that  at  any  given  rate  of 
driving  the  difference  in  economy  between  the  best  and  the  poorest 
results  may  be  as  much  as  30  per  cent,  even  under  test  conditions  with 
supposedly  expert  firing,  when  the  boiler  is  hand-fired  and  the  air- 
supply  is  not  controlled  in  accord  with  the  results  of  gas  analyses  or 
with  the  record  of  a  C02  indicator. 

Commenting  on  the  results  plotted  in  Fig.  262  the  author  many 
years  ago  made  the  statement  that  the  relation  between  the  economy 
and  the  rate  of  driving  of  a  boiler  was  not  expressed  by  any  formula 
cr  curve,  but  by  a  broad  field  whose  upper  boundary  represented  the 
results  that  could  be  obtained  under  the  best  conditions,  and  whose 
breadth  (it  was  very  broad)  represented  the  depth  of  our  ignorance  as 
to  what  were  the  best  conditions  and  how  they  could  be  obtained.  At 
that  time  there  was  no  Orsat  or  Hempel  gas  apparatus  or  C02  indicator, 
and  no  one  knew  what  composition  of  gas  was  coincident  with  the 
best  efficiency.  The  field  of  ignorance  is  now  narrowed,  so  that  with 
analysis  of  the  gas  and  of  the  fuel,  with  mechanical  stokers,  and  with 
provision  against  loss  by  radiation,  air-leakage  and  short-circuiting, 
the  probable  performance  of  a  boiler,  under  known  conditions  of 
air-supply  and  rate  of  driving,  may  be  predicted  within  a  margin  of 
error  of  not  over  five  per  cent. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


629 


Highest  Efficiency  with  Anthracite. — Taking  the  heating  value 
of  the  coal  used  in  the  Centennial  tests  at  14,900  B.T.U.  per  Ib.  of 
combustible,  the  six  boilers  giving  the  highest  results  show  the  follow- 
ing: 


Name  of  Boiler. 

Rate  of 
Driving,  W/S. 

Evaporation  per  Ib. 
Combustible. 

Efficiency, 
Per  cent. 

Root. 

2  59 

12  094 

78  77 

Firmenich 

1  93 

11  988 

78  08 

Lowe   . 

2.15 

11  923 

77  65 

Smith. 

2  79 

11.906 

77  55 

Smith. 

3  74 

11.925 

77  67 

Babcock  &  Wilcox. 

2  79 

11.822 

77  00 

Galloway  

4.83 

11.583 

75.44 

Galloway  

5.41 

11.216 

73.05 

The  favorable  conditions  which  led  to  obtaining  these  high  results 
were:  Selected  egg  coal,  dry  and  low  in  ash;  expert  firing;  low  tem- 
perature of  water  in  the  boiler.  It  is  not  to  be  expected  that  these 
results  can  be  equaled  in  modern  practice  with  small  sizes  of  anthra- 
cite, except  by  the  use  of  mechanical  stokers  and  control  of  the  air 
supply  with  the  aid  of  gas  analyses. 

Impossible  Boiler  Performances.  (Power,  Jan.  17, 1911). — There 
are  being  circulated  printed  records  of  tests  conducted  at  the  plant  of 
the  American  Printing  Company,  Fall  River,  Mass.,  upon  horizontal 
return-tubular  boilers,  in  which  an  evaporation  of  16.69  Ibs.  of  water 
from  and  at  212°  is  claimed. 

Assuming  that  each  pound  of  combustible  makes  20  Ibs.  of  gas 
and  that  the  gas  leaves  the  boiler  400°  above  the  room  temperature, 
such  a  performance  would  call  for  a  coal  of  over  18,000  B.T.U.  per 
pound  of  combustible,  even  allowing  nothing  for  radiation;  and  no 
such  coal  has  ever  been  mined. 

At  the  time  that  this  impossible  performance  is  claimed  to  have 
been  effected  the  boilers  were  fitted  with  a  device  known  as  the  Cornell 
fuel  economizer.  This  consists  of  a  number  of  metallic  retorts  behind 
the  bridge  wall,  into  which  steam  is  admitted,  and  it  is  claimed  that 
the  steam  in  passing  through  them  is  decomposed  into  its  constituent 
gases,  oxygen  and  hydrogen,  and  that  it  is  the  combustion  of  the 
hydrogen  which  supplies  the  extra  heat  necessary  to  obtain  the  high 
evaporation  reported. 

This  claim  has  been  exploded  over  and  over  again  in  Power. 
Even  if  the  steam  is  so  decomposed  it  takes  as  much  heat  to  decompose 
it  as  the  gases  produced  will  generate  in  combustion.  When  hydrogen 
is  burned,  two  atoms  of  hydrogen  unite  with  one  of  oxygen  to  form 
TT.,0  or  water  vapor — steam.  The  decomposition  of  steam  into  hydro- 
gen and  oxygen  is  a  reversal  of  the  process,  and  takes  just  as  much 


630  STEAM-BOILER  ECONOMY. 

energy  in  the  form  of  heat  as  was  produced,  or  will  be  produced  again, 
by  the  reunion  of  the  gases  in  combustion.  (See  Heat  Absorbed,  by 
Decomposition,  page  22.) 

Test  of  a  Corliss  Vertical  Tubular  Boiler  with  Anthracite. — In 
connection  with  a  test  of  the  Pawtucket,  R.  I.,  pumping  engine  in 
1889  by  Prof.  J.  E.  Denton,*  a  72-hour  test  was  made  of  three  Corliss 
vertical  tubular  boilers,  with  stove  size  anthracite.  Each  boiler  had 
48  3-in.  tubes,  14  ft.  long.  The  total  heating  surface  in  contact  with 
water  in  the  three  boilers  1231  sq.  ft.,  and  the  superheating  surface 
508  sq.  ft.  The  total  grate  surface  was  45  sq.  ft.  The  test  is  re- 
markable in  showing  high  economy,  12.11  Ibs.  evaporated  from  and 
at  212°  per  Ib.  combustible,  or  76.5%  of  efficiency,  at  a  very  low  rate 
of  driving,  1.58  Ibs.  water  evaporated  from  and  at  212°  per  sq.  ft. 
of  heating  surface  per  hour,  and  4.9  Ibs.  coal  burned  per  sq.  ft.  grate 
per  hour.  The  analysis  of  the  coal  was  as  follows:  Moisture,  1.80; 
ash,  6.90;  C,  79.30;  H,  4.60;  S,  0.85;  0,  4.65;  N,  1.90.  B.T.U. 
per  Ib.  combustible,  by  Dulong's  formula,  14,876.  During  the  test 
the  coal  showed  3%  moisture.  The  average  analysis  of  the  gases  was 
C02,  8.7;  CO,  0.3;  0,  10.8;  N,  80.3;  corresponding  to  20.85  Ibs.  gas 
per  pound  of  coal. 

Tests  of  a  Rust  Water-tube  Boiler  with  Pittsburgh  Coal . — The 

accompanying  table  gives  the  principal  results  of  two  tests  made  by 
the  author  in  1906  on  a  Rust  water-tube  boiler  rated  at  335  H.P., 
provided  with  a  Roney  stoker  and  an  extension  furnace.  One  test 
was  made  to  determine  the  economy  when  driven  at  or  near  the 
builders'  rating  and  the  other  to  determine  the  capacity  when  driven 
at  the  highest  rate  the  chimney  draft  would  permit.  The  results  were 
the  highest  on  record  at  that  date  for  coal  containing  over  30  per 
cent  of  volatile  matter  in  the  combustible,  and  they  have  been  ex- 
ceeded since  with  similar  coal  only  with  boilers  provided  with  exceed- 
ingly large  combustion  chambers  and  when  the  rate  of  feeding  coal 
and  the  force  of  draft  were  controlled  in  accordance  with  the  indica- 
tions of  chemical  analyses  of  the  flue  gases.  The  following  notes  are 
taken  from  the  author's  report  of  these  tests. 

The  results,  high  as  they  are,  can  undoubtedly  be  duplicated  at 
any  time  when  the  same  conditions  under  which  these  tests  were  made 
can  be  obtained,  viz.,  uniform  rate  of  driving,  without  having  to  shut 
off  the  draft  at  any  time  during  the  day  to  lower  the  steam  pressure, 
and  without  having  to  force  the  fires  to  raise  the  pressure ;  the 
boiler  clean  inside  and  out;  a  fire-brick  furnace  and  an  automatic 

*  Tenth  Annual  Report  of  the  Water  Commissioners,  City  of  Pawtucket, 
R.  I.,  1890. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


631 


stoker;  the  brickwork  free  from  leaks  of  air;  the  draft  and  rate  of 
feeding  the  coal  adjusted  to  each  other  so  as  to  burn  the  coal  without 
smoke  and  without  any  greater  excess  or  air  than  is  necessary  for 
complete  combustion;  and  practically  no  loss  of  coal  through  the 
grate  bars. 

TESTS   OF  THE    RUST   WATER-TUBE    BOILER,    1906. 


apac 
Test. 


city 


Economy 
Test. 


Duration  of  trial Hours 

Weight  of  coal  as  fired Lbs. 

Moisture  in  coal Per  cent 

Ash  and  refuse  in  dry  coal Per  cent 

Equivalent  water  evaporated  from  and  at 

212°  into  dry  steam Lbs. 

Dry  coal  per  sq.  ft.  of  grate  surface  per  hour  Lbs. 
Evaporation  from  and  at  212°: 

per  sq.  ft.  heating  surface  per  hour  .  .         Lbs. 

per  Ib.  coal  as  fired Lbs. 

per  Ib.  dry  coal Lbs. 

per  Ib.  combustible Lbs. 

Horse-power  developed B.T.U. 

Per  cent  of  builder's  rated  power  developed.        H.P. 

Calorific  value  of  the  dry  coal  per  Ib B.T.U. 

Calorific  value  of  the  combustible  per  Ib. .  .  .  B.T.U. 
Efficiency  of  he  boiler  (based  on  combustible)  Per  cent 
Efficiency  of  the  boiler,  furnace  and  grate 

(based  on  dry  coal) Per  cent 

Force  of  draft  at  base  of  stack Av'ge  in. 

' '       "        between  damper  and 

boiler 

' '       ' '        over  fire 

Range  of  draft  pressures,  flue Ins. 

furnace 

differences 

Moisture  in  steam Per  cent 

Temperature  of  gases  escaping  from  boiler .  .    Deg.  F. 

Temperature  of  feed  water Deg.  F. 

Steam  pressure,  by  gage Lbs.  per  sq.  in. 

Grate  surface,    68   sq.ft.,    Roney   stoker.       Heating 
surface  3350  sq.  ft. 


8 

21,310 

3.00 

13.29 

194,643 
38.00 

7.26 
9.134 
9.416 
10.859 
705.2 
210.5 
13,202 
15,161 
69.17 

68.88 
1.05 


0.72 

0.34 
65toO 
24  to  0.41 
30  to  0 . 

0.83 
718 
42 
137 


.780 


480 


10 

11,850 

2.47 

14.01 

121,511 
17.01 

3.63 
10.254 
10.505 
12.216 

352.2 

105.1 
13,428 
15,554 
75.85 

75.55 
1.1 

0.32 
0.17 

.25  to  0.37 
0.08  to  0.23 
10  to  0.18 

0.70 
503 
42 
132 


Each  test  was  started  with  the  hopper  full  of  coal  and  the  boiler 
in  running  condition,  the  fires  having  been  thoroughly  cleaned  an  hour 
previously.  The  test  was  stopped  in  the  same  condition.  The  coal  was 
of  the  quality  regularly  used  in  the  works.  It  may  be  classed  as 
crushed  run-of-mine,  and  contained  lumps  of  all  sizes  from  3-in.  cube 
down  to  fine  slack.  The  quality  differed  on  the  two  days,  according 
to  the  chemical  analysis.  The  draft  was  regulated  by  a  damper  in 
the  flue  leading  to  the  stack,  it  being  kept  wide  open  during  the 
capacity  test,  and  fixed  at  less  than  half  opening  during  the  economy 
test.  The  draft  in  the  stack  remained  nearly  constant. 

A  study  of  the  conditions  of  draft  in  the  furnace  and  flue  as 


632 


STEAM-BOILER  ECONOMY. 


shown  by  an  Ellison  or  other  multiplying  draft  gage  may  be  of 
considerable  service  in  leading  to  improving  both  the  capacity  and 
the  economy  of  a  boiler  plant.  The  draft  in  the  stack,  the  atmos- 
pheric pressure  under  the  grates,  and  the  resistance  to  the  passage  of 
gas  through  the  boiler  structure  are  all  nearly  constant  for  a  given 
boiler.  The  principal  variable  condition  is  the  resistance  offered  by 
the  coal  on  the  grate,  and  this  condition  is  indicated  by  the  reading 
of  the  two  draft  gages,  one  at  the  furnace  and  the  other  at  the  flue 
between  the  boiler  and  the  damper.  When  the  difference  between 
the  readings  of  the  two  gages  is  smaller  than  normal  it  indicates  that 
a  small  quantity  of  gas  is  passing  through  the  boiler  structure,  which 
may  be  due  to  a  choked  grate,  and  this  indication  is  confirmed  if 
the  draft  in  the  furnace  is  higher  than  normal.  If  the  difference  is 
greater  than  normal  and  the  draft  in  the  furnace  is  light,  there  is 
too  thin  a  bed  of  coal  on  the  grate,  or  on  part  of  it,  and  an  excessive 
quantity  of  air  is  passing  into  the  furnace. 

Tests  of  a  640  H,P.  B,  &  W.  Boiler  with  a  Taylor  Stoker.— From 
the  results  of  a  series  of  19  tests  made  at  the  Waterside  station  of 
the  N.  Y.  Edison  Co.,  in  1907,  the  following  figures  for  13  tests  with 
semi-bituminous  coal  are  selected : 


4.79 

4.82 

W/S.  .Ibs. 

3.55 

3.74 

4.12 

4.45 

4.52 

4.61 

4.61 

4.65 

4.99 

6.30 

6.51 

E  % 

73.1 

74.2 

79.3 

80.7 

80.9 

78.7 

75.8 

80.7 

75.1 

80.7 

77.6 

76.6 

74.5 

Ei,  by  for- 

mula .  .  . 

81.4 

81.0 

80.3 

79.6 

79.5 

79.3 

79.3 

79.2 

78.9 

78.9 

78.5 

75.9 

75.5 

-DiK.Ei-E 

-8.3 

-6.8 

-1.0 

+  1.1 

+1.4 

-0.6 

-3.5 

+  1.5 

-3.8 

+  1.8 

-0.9 

+0.7 

-1.0 

Radiation, 

etc,  %  . 

14.6 

14.6 

10.0 

6.8 

7.7 

9.1 

13.0 

8.3 

13.6 

7.7 

13.0 

12.5 

15.1 

The  formula  with  which  the  boiler  efficiency  E  is  compared  is 
E  =  82.5  —  2 (W/S  —  3) .  It  is  abtained  by  plotting  the  efficiencies  ob- 
tained at  rates  of  evaporation  in  excess  of  4  Ibs.  per  sq.  ft.  of  heating 
surface  per  hour.  Tbe  results  are  somewhat  erratic,  and  the  variation 
in  composition  of  the  flue  gases  (C02  10.9  to  16.5,  0,  1.3  to  7.9)  is 
not  sufficient  to  account  for  them.  It  is  noticeable  that  all  the  results 
that  show  efficiencies  lower  than  those  calculated  from  the  formula 
also  show  high  losses  due  to  radiation  and  unaccounted  for.  The 
actual  loss  by  radiation  was  probably  not  much  in  excess  of  1%.  The 
unaccounted  for  loss  may  be  largely  due  to  incomplete  combustion  of 
CH4  distilled  from  the  coal  and  of  IT  from  the  decomposition  of  moist- 
ure in  the  coal,  which  was  rather  high  (2.2  to  4.0%)  for  semi-bitu- 
minous. The  great  fluctuations  in  the  unaccounted  for  loss  under  con- 
ditions that  were  uniform  so  far  as  could  be  ascertained  indicate  errors 
in  the  coal  measurement,  due  to  the  fact  that  the  tests  were  not  over  8 
hours  long,  and  the  difference  in  quantity  and  condition  of  the  coal 
on  the  grates  at  the  beginning  and  end  of  a  test  might  be  considerable. 
The  furnace  conditions  were  not  the  most  favorable  for  high  economy 
at  rapid  rates  of  driving,  for  the  stoker  was  installed  in  the  old  setting 
of  the  boiler  which  had  only  a  moderate  sized  combustion  space.  The 


RESULTS  OF  STEAM-BOILER  TRIALS. 


633 


temperature  of  the  chimney  gases  was  low  in  all  the  tests,  ranging 
from  418°  F.  for  W/8  =  3.55  to  519  for  W/S  =  6.51.  At  the  date 
named  (1907)  the  efficiencies  were  the  highest  that  had  ever  been 
obtained  at  rates  of  driving  in  excess  of  4  Ibs.  from  and  at  212°  per 
sq.  ft.  of  heating  surface  per  hour.  Of  the  other  six  tests  of  the 
series,  five  were  made  with  bituminous  coal,  averaging  27.4%  volatile 
matter  in  the  combustible,  and  much  lower  efficiencies  were  obtained, 
as  below : 


W/S 

E.  . 


3.78 
71.5 


3.98 

74.4 


4.80 
69.4 


4.88 
76.4 


5.32 
73.9 


One  test  was  made  with  coke  at  a  low  rate  of  driving,  giving  W/8 
=  3.98,  E  =  73.6%. 

Tests  with  Taylor  Stokers. — The  following  condensed  summary  is 
abstracted  from  the  reports  of  numerous  tests  published  by  the 
American  Engineering  Co.,  makers  of  the  Taylor  stoker: 


No. 

Kind  of  Boiler. 

Per  cent 
of 
Rating. 

W 

S 

Efficiency 
of  Boiler 
and 
Furnace. 

Gas  Analysis. 

Temp, 
of  Flue 
Gases. 

Duration 
of  Test, 
Hours. 

CO* 

O 

CO 

1 

B.       W. 

175 

6.04 

77.6 

12.7 

6.7 

0 

449 

24 

2 

1 

130 

4.50 

78.6 

11.9 

7.5 

0 

429 

24 

3 

1 

249 

8.59 

71.6 

13.4 

5.5 

0.09 

527 

4 

4 

• 

244 

8.42 

72.6 

15.5 

1.9 

0.96 

498 

4 

5 

• 

190 

6.56 

74.4 

599 

12 

6 

Manning 

147 

4.89 

76.4 

io.i 

j'.8 

6   " 

600 

5 

7 

1 

151 

5.01 

71.0 

13.3 

7.0 

0 

598 

24 

8 

• 

151 

5.02 

71.8 

11.8 

7.7 

0 

599 

24 

9 

4 

150 

4.97 

72.1 

12.4 

7.3 

0 

599 

39 

10 

B.  &  W. 

180 

6.15 

76.8 

12.7 

544 

8 

11 

* 

117 

4.12 

78.5 

13.3 

5^9 

6" 

455 

8 

12 

• 

127 

4.45 

79.6 

12.2 

7.5 

0 

473 

8 

13 

1 

129 

4.52 

79.8 

13.0 

6.2 

0 

468 

8 

14 

* 

131 

4.61 

77.1 

12.7 

6.5 

0 

468 

8 

15 

• 

131 

4.61 

75.3 

13.5 

5.8 

0 

473 

8 

16 

1 

137 

4.82 

77.6 

13.5 

4.7 

0 

492 

8 

17 

' 

142 

4.99 

76.5 

16.2 

1.4 

0 

475 

8 

18 

' 

185 

6.51 

72.7 

16.5 

1.3 

519 

3.85 

19 

Edge  Moor 

188 

6.36 

71.3 

12.4 

5.8 

6" 

546 

16 

20 

Geary 

82 

2  77 

70  2 

370 

16 

21 

155 

5.37 

76.8 

430 

4 

22 

Stirl  ng 

133 

4.58 

76.1 

14  !  5 

8 

23 

B.  &  W. 

139 

4.80 

79.7 

13.3 

6.4 

0.22 

577 

8 

24 

Stir  mg 

151 

5.22 

77.1 

14.0 

5.5 

0.42 

575 

24 

25 

1 

108 

3.72 

80.3 

13.7 

5.8 

0.10 

493 

24 

26 

163 

5.62 

77.8 

14.7 

4.6 

0.12 

574 

50 

27 

1 

93 

3.22 

77.9 

11.9 

8.0 

0.06 

487 

48 

28 

• 

211 

7.29 

75.8 

15.4 

3.9 

0.17 

651 

26.5 

29 

• 

121 

4.18 

79.2 

13.8 

5.7 

0.04 

535 

48 

30 

•  • 

185 

6.40 

76.4 

14.2 

5.1 

0.08 

647 

24 

31 

(?) 

104 

3  58 

78  5 

516 

8 

32 

B.  &  W. 

167 

5.78 

72.4 

553 

7 

33 

Ret.Tubular 

136 

4.69 

77.0 

12.5 

430 

6 

34 

Edge  Moor 

159 

5.47 

78.2 

14.3 

3.9 

6!24 

499 

12 

NOTES:    TF/S=lbs.  water  evaporated  from  and  at  212°  per  sq.  ft.  heating  surface  per  hour 
Kind  of  coal:    Nos.  1  to  22,  semi-bituminous,  Nos.  23  to  34,  bituminous.     Location  of  boilers, 

I  to  4,  Boston  Elevated  Railway  Co.,  South  Boston;    5,  Old  Colony  Ry.  Co.,  Quincy,  Mass., 
6  to  9,  Everett  Mills,  Lawrence,  Mass.;    10,  Narragansett  Elec.  Lt.  Co.,  Providence,  R.  I.; 

II  to  18,  New  York  Edison  Co.,  Waterside  Station;  19,  N.  Y.  Central  R.  R.  Co.,  Albany,  N.  Y.- 
20,  21,  National  Museum,  Washington,  D.  C.;   22,  Wardlaw-Thomas  Paper  Co.,  Middletown, 
O.;  23,  Cleveland,  O.,Ry.Co.;   23  to  30,  Detroit  Edison  Co.;   31,  Public  Lighting  Co.,  Detroit, 
32,  Commonwealth  Edison  Co.,  Chicago;    33,  Fox  River  Paper  Co.,  Appleton,  Wis.;    34; 
Milwaukee  El.  Ry.  &  Light  Co. 


634 


STEAM-BOILER  ECONOMY. 


In  the  Manning  boiler  tests,  Nos.  6  to  9,  the  heat  balance  shows 
the  "radiation  and  unaccounted  for"  loss  in  the  four  tests  to  be  7.8, 
14.3,,  12.8  and  13.2  per  cent.  Mr.  Chas.  H.  Manning,  who  reports  the 
tests,  says  of  Xo.  6,  "the  results  give  an  exaggerated  efficiency"  due 
to  an  error  in  the  coal  measurements.  It  is  not  to  be  expected  that 
a  5-hour  test  will  give  results  that  are  even  approximately  accurate, 
but  "the  radiation  and  unaccounted  for"  losses  in  the  other  three 
tests  are  unusual  for  semi-bituminous  coal.  The  low  efficiency  in 
these  tests  is  accounted  for  by  the  facts  that  the  tubes  were  much 
clogged  with  soot,  a  reason  for  the  high  temperature  of  the  waste 
gases,  and  that  the  plant  was  run  by  men  of  short  experience  with 
the  stokers. 

Another  series  of  tests  with  the  Taylor  stoker  is  reported  by 
Horace  Judd  in  Power,  June  23,  1914.  The  first  six  were  made 
on  a  Babcock  &  Wilcox  cross-drum  boiler  of  2485  sq.  ft.  of  heating 
surface  and  the  other  four  on  a  Flannery  cross-drum  water-tube 
boiler  of  3130  sq.  ft.  of  heating  surface.  Coals  of  rather  low  grade 
were  used,  the  heating  value  per  pound  of  combustible  ranging  from 
14,191  to  14,980  B.T.U.  The  results  were  in  general  considerably 
lower  than  those  given  in  the  above  table,  which  may  be  accounted 
for  by  the  smaller  size  of  boilers,  which  would  make  the  percentage 
of  radiation  loss  greater,  the  lower  grade  of  coal,  and  the  higher 
percentage  of  moisture  in  the  coal  (2.73  to  11.62  per  cent).  The  tests 
were  only  of  10  hours  duration  each,  which  might  cause  an  error  of 
3  or  4  per  cent  in  the  recorded  results,  on  account  of  the  possible 
variation  in  quantity  and  quality  of  the  partially  burned  coal  in  the 
furnace  at  the  beginning  and  end  of  the  tests.  The  most  important 
lesults  are  the  following: 


No  of  test 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

Rate  of  driving,  W/S  
Efficiency,  boiler  and  furnace.  . 
Efficiency,  b.,  f.,  and  grate..  .  . 
Radiation,  etc  

5.90 
71.8 
69.9 
7.19 

5.84 
77.3 
72.5 
1.25 

5.12 

74.7 
69.9 
5.65 

5.68 
69.4 
67.1 
8.39 

6.02 
69.3 
66.3 
9.75 

5.76 
66.7 
63.5 
12.93 

4.33 
71.0 
67.6 
12.17 

5.76 

65.8 
12.48 

6.38 
66.0 
59.0 
15.82 

7.00 
68.1 

11.41 

The  great  fluctuation  in  the  loss  by  radiation  and  unaccounted 
for,  from  the  impossibly  low  figure  1.25  to  the  very  high  figure  15.82, 
is  evidence  of  large  errors  in  the  coal  record  of  these  tests. 

Mr.  Judd  says  in  his  report  of  these  tests :  The  chief  controlling 
factors  influencing  the  efficiency  of  a  Taylor  stoker  at  overload 
capacity  appear  to  be: 


RESULTS  OF  STEAM-BOILER  TRIALS. 


635 


1.  Size  of  the  unit. 

2.  Percentage  of  overload. 

3.  Character  of  coal. 

4.  The  use  of  indicating  boiler  room  appliances. 

5.  The  intelligence  of  the  fireman. 

The  factor  of  most  importance  is,  without  doubt,  the  degree  of 
intelligence  which  the  fireman  possesses  and  the  interest  he  takes  in 
improving  the  operating  conditions. 

Test  of  an  Edge  Moor  Water-tube  Boiler. — Three  tests  of  an 
Edge  Moor  water-tube  boiler  with  a  Taylor  stoker  and  Foster  super- 


FIG.  270. — EDGE  MOOR  BOILER  WITH  TAYLOR  STOKER  AND  FOSTER  SUPER- 
HEATER. 


heater  were  made  at  the  Westport  station  of  the  Consolidated  Gas, 
Electric  Light  and  Power  Co.,  of  Baltimore  in  1913.  A  sectional 
view  of  the  boiler  and  setting  is  shown  in  Fig.  270.  The  coal 
tests  are  given  below.  The  first  two  tests  were  each  8  hours  long ;  the 
third  2  hours,  no  coal  record  being  made. 


636 


STEAM-BOILER  ECONOMY. 


Per  cent  of  rating  developed 

210  5 

248  5 

318 

Steam  pressure  pounds  per  square  inch  gage 

169  7 

167  4 

172  1 

Superheat  deg  Fah. 

130  4 

106  6 

103  5 

Pressure  in  tuyere  box,  ins  .  of  water  

2.69 

3.68 

5  3 

Draft  in  furnace  ins.  of  water. 

09 

03 

Draft  at  bottom  of  last  pass,  ins.  of  water  

.76 

.88 

1.2 

Coal  as  fired  per  hour 

5031 

6000 

Coal  per  square  foo    grate  per  hour  (total  grate 
surface  120  sq.  ft.)  '.  

42 

50 

Temperature  of  escaping  gases,  deg.  Fahr  
Average  interval  between  dumpings,  hours  
Equivalent  evaporation  per  pound  of  dry  coal,  Ibs. 
Equivalent  evaporation  per  square  foot  of  water- 
heating  surface  per  hour  pounds 

550.6 
2.6 
10.98 

7  26 

584.7 
2.0 
10.77 

8  57 

10  97 

Horsepower  developed  (rated  H.P.,  736)  
Efficiency  of  boiler  and  grate,  per  cent  

1549 

74.7 

1829 

72.8 

2340 

Moisture  in  coal 

3  27 

2  39 

Volatile  matter 

19  73 

18  62 

Ash 

9  43 

8  74 

Sulphur  separately  determined 

1  93 

1  63 

B  T  U  per  pound  coal 

13  797 

14018 

lt        "        tf      combustible 

15,804 

15,683 

Gas  analyses  —  above  damper: 
CO2.  .  , 

15.6 

16.1 

o 

3  4 

2  6 

CO 

0  03 

0  16 

Appearance  of  smoke 

Haze 

Light 

gray 

Value  of  the  Rear  Passes. — Referring  to  the  cut,  Figs.  A,  B,  and 
C  show  the  positions  where  the  thermo-couples  of  an  electric  pyrometer 
were  placed.  The  couples  were  moved  in  and  out  until  a  position  was 
found  where  the  temperature  indicated  was  highest.  The  average 
of  several  readings  obtained  in  the  two  8-hour  tests  were  as  follows: 


At  about  210%  of  Rating. 
At  A  AtB  AtC 

918°  618°  560° 

Diff.  300  58 


At  about  248%  of  Rating. 
At  A  AtB          At  C 


1005 c 


684C 


609 c 


321' 


75' 


The  report  of  the  test  contains  the  following: 

With  high  percentage  CO,  and  good  coal,  the  rise  in  efficiency 
or  the  percentage  of  the  calorific  value  of  the  coal  absorbed.,  per  100 
degrees  drop  of  gas  temperature  is  about  2.75  per  cent.  On  this  basis 
the  gain  in  efficiency  due  to  the  last  pass  or  from  B  to  C  is  a  little 
more  than  1.6%  at  210%  of  rating,  and  2.1%  at  248%  of  rating. 
The  percentages  of  the  total  heating  surface  (including  superheater) 
in  the  different  sections  of  the  boiler  are,  approximately,  from  the 
fire  to  A,  45% ;  from  A  to  B,  40% ;  from  B  to  C,  15%.  The  per- 
centage of  the  calorific  value  of  the  coal  absorbed  in  the  different 
sections  is,  approximately  as  follows: 


RESULTS  OF  STEAM-BOILER   TRIALS. 


637 


Sections. 

F  to  A. 

A  to  B. 

B  to  C. 

Total. 

Per  cent  of  heating  surfacs.  . 

45 

40 

15 

100 

Absorbed  at  210%  of  rating.  .  . 
"  248%  of  rating  

64.9 
61.9 

8.2 
8.8 

1.6 

2.1 

74.7 
72.8 

PER  CENT  OF  THE  TOTAL  HEAT  ABSORBED. 


At  210%  of 

rating  

86  9 

11  0 

2  1 

100 

At  248%  of 

rating.  . 

85  0 

12  1 

2  9 

100 

Let  it  be  supposed  that  in  the  test  at  248%  of  rating  the  gases 
were  allowed  to  escape  at  A.  Only  45%  of  the  total  heating  surface 
would  then  have  been  in  use,  while  85 %  of  the  total  steam  would 
have  been  generated.  This  would  give  an  equivalent  evaporation 
per  hour  of  15.3  Ibs.  per  square  foot  of  heating  surface,  and  a  per- 
centage of  rated  capacity,  based  on  10  sq.  ft.  of  surface  per  horse- 
power, equal  to  443%.  The  efficiency  would  then  have  been  61.9% 
and  the  gases  would  then  have  escaped  at  1005°. 

Considering  the  decreasing  efficiency  of  the  heating  surface  as 
the  temperature  drops,  a  boiler  may  be  logically  divided  into  two 
sections — the  capacity  section,  which  includes  the  hotter  surface, 
and  the  economizer  section,  which  includes  the  colder  surface.  The 
question  has  sometimes  been  raised  if  it  really  pays  to  put  in  this 
economizer  section. 

An  analysis  of  the  fixed  and  maintenance  charges  on  this  part 
of  the  boiler  will  show  that  for  land  service  the  investment  is  nearly 
always  a  very  profitable  one.  This  is  because  the  first  cost  is  com- 
paratively small,  while  the  maintenance  is  negligible.  The  heating 
surface  being  practically  all  tube  surface  (the  fronts,  headers,  etc., 
being  the  same  whether  the  tubes  are  long  or  short),  is  therefore 
inexpensive,  while  the  costs  of  the  additional  size  of  building,  the 
extra  brickwork  and  slight  extra  height  of  chimney  required  do  not 
amount  to  a  great  deal.  The  determining  factor  may  be  the  extra 
real  estate;  but  seldom  will  it  occur  that  the  saving  in  fuel  due 
to  the  extra  efficiency  gained  will  not  show  a  most  desirable  net 
profit. 

Time  Required  to  Obtain  a  High  Rate  of  Evaporation  from 
a  Banked  Fire. — The  Edge  Moor  boiler  referred  to  above  was  kept 
idle  with  a  smouldering  banked  fire  for  an  entire  week,  coal  being 
fed  at  the  rate  of  about  220  Ibs.  per  hour.  At  the  end  of  the  week 
the  fuel  bed  was  in  poor  condition  and  the  brickwork  was  cold. 
Fresh  coal  was  then  fired  and  forced  draft  applied.  The  steam 
meter  records  were  plotted  every  half  minute,  and  they  showed 
that  the  times  required  for  the  boiler  to  furnish  steam  at  different 
percentages  of  the  boiler's  rating  were  as  follows: 


Per  cent  of  rating , 
Time  in  minutes. . 


50 
1.7 


100 
2.3 


150 
4.7 


200 

7.8 


638  STEAM-BOILER  ECONOMY. 

Recent  Experience  with  the  Delray   (Detroit)  Boilers.     (J.  W. 

Parker,  Jour.  A.  S.  M.  E.,  1913.) — Since  the  first  performance 
tests,  in  1911,  six  more  of  the  same  type  and  size  (Stirling  W  type, 
2365  H.P.  each)  have  been  installed,  the  last  two  in  the  autumn  of 
1913.  From  Oct.  15,  1912,  to  Nov.  1,  1913,  there  have  been  but  two 
tubes  replaced  in  seven  boilers  whose  average  age  is  two  years.  Taking 
all  stoppages  in  consideration,  including  those  for  repairs  of  brick-work 
and  of  stokers,  the  boilers  were  ready  for  service  95%  of  the  time ;  98% 
of  the  five  full  load  days  of  the  week,  and  100%  of  the  peak  load 
periods. 

The  Detroit  Edison  Company  is  now  building  a  power  plant  to 
contain  six  20,000  KW.  turbines  served  by  12  2365  H.P.  boilers, 
which  is  two  boilers  to  one  turbine,  with  no  spares,  or  10,000  KW.  per 
boiler.  At  normal  full  load  on  a  given  turbine  unit,  the  two  boilers 
will  operate  at  approximately  191%  of  the  builder's  rating  based  on 
10  sq.  ft.  of  heating  surface  per  boiler  horse-power.  If,  with  six 
boilers  running  at  this  rating,  one  boiler  should  go  completely  out 
of  commission,,  the  other  five  would  have  to  carry  the  entire  load  of 
60,000  KW  and  thus  operate  at  235%  of  rating,  which  is  perfectly 
possible.  The  settings  and  auxiliaries  are  being  designed  to  allow 
of  continuous  operation  at  255%  of  rating,  which  would  enable  three 
boilers  to  take  the  full  load  of  four,  i.  e.  40,000  KW.  Eecently,  one 
of  the  Delray  boilers  was  isolated  from  the  rest  of  the  plant  with  a 
15,000  KW.,  seven-stage  Curtis  vertical  turbine,  and  over  11,000  KW. 
was  carried  for  an  hour  without  difficulty. 

Method  of  Operating  the  Delray  Boilers. — It  is  economical  to  run 
as  many  boilers  as  possible  at  about  90%  of  rating  when  the  plant 
load  is  light,  and  then  carry  the  peak  of  the  load  by  increasing 
the  rating  on  the  boilers.  In  this  way,  from  morning  till  night 
there  need  be  no  fires  banked  or  broken  out  of  bank.,  and  the  firemen 
can  bend  their  energies  instead  to  manipulating  their  fires  to  the 
best  advantage. 

This  flexibility  is  at  no  time  more  convenient  than  in  summer 
when  provision  must  be  made  for  a  sudden  peak  "oad  due  to  a 
thunderstorm.  At  Delray,  in  the  summer  of  1914  the  average  day 
load  will  be  about  63,000  KW.,  while  provision  must  be  made  for 
a  storm  load  of  about  82,000  KW.,  a  30  per  cent  increase.  Boilers 
ordinarily  running  at  100  per  cent  or  125  per  cent  of  rating  (a  very 
economical  point)  will  take  a  30  per  cent  increase  in  load  with  very 
little  effort.  No  banked  fires  will  be  carried  during  the  daytime. 

One  fireman  fires  two  units.  The  control  of  each  unit  is  brought 
directly  under  his  hand  in  every  way  possible,  so  that  a  minimum 
of  time  will  be  wasted  in  mechanical  manipulation.  A  water  tender 
stationed  on  a  gallery  at  the  top  drum  level  feeds  the  boiler,  but  the 
fireman  does  everything  else  in  the  way  of  operating.  The  plan  is 
for  one  man  to  operate  two  stokers,  and  in  addition,  to  have  a  head 
fireman  in  charge  of  from  six  to  eight  units,  whose  duty  it  is  to 
oversee  all  the  fires,  and  go  to  the  assistance  of  any  fireman  who  needs 


RESULTS  OF  STEAM-BOILER  TRIALS.  639 

help.  On  the  gage  board  are  mounted  steam  gages  showing  pressure 
at  the  superheater  inlet  and  superheater  outlet  and  draft  gages  show- 
ing air  pressure  under  the  fire,  draft  at  the  damper,  and  draft  at  the 
top  of  the  combustion  chamber.  There  is  also  on  this  board  the  record 
dial  of  a  C02  meter.  Four  samples  of  gas  are  drawn  from  one 
furnace,  automatically  mixed,  and  the  resulting  analysis  is  recorded 
where  the  fireman  can  watch  it. 

Fireroom  Personnel.  The  whole  idea  is  to  employ  the  most  ex- 
pert firemen  it  is  possible  to  develop,  and  give  each  man  control  of 
the  burning  of  a  very  large  amount  of  coal.  It  is  economical  to  em- 
ploy a  fine  type  of  man  and  pay  him  an  expert's  pay.  The  present 
first-class  fireman's  pay  is  40  cents  an  hour  and  he  is  well  treated  as 
to  vacation  and  sick  leave.  A  force  of  firemen  is  being  built  up 
that  can  obtain  remarkable  results  with  their  fires.  They  are  ac- 
quiring an  intelligent  understanding  of  the  combustion  of  coal. 
At  the  same  time  the  unit  cost  of  firing  is  unusually  low. 
The  following  table  is  a  schedule  of  the  labor  necessary  to  handle  12 
boilers  of  a  six-turbine  plant  with  no  economizers  installed : 

LABOR    COST   OF    FIRING    A   TWELVE    BOILER    PLANT. 

Maximum  load 120,000  kw.    12  boilers  at  191% 

Minimum  load .     20,000  kw.     4  boilers  at    96% 

Monthly  load  factor  (November) 46% 

Operators  employed :  20 

Morning  shift       6.30-  2.30     2  head  firemen  at  45  cents $7.20 

6  firemen  at  40  cents 19 . 60 

2  watertenders  at  35  cents 5 . 20 

Afternoon  shift    .2.30-10.30    2  head  firemen 7 . 20 

6  firemen 19.60 

2  watertenders 5 . 20 

Night  shift          10.30-  6.30     6  firemen 19 . 80 

1  watertender.  .  2.00 


$86.00 
15.00 


Total  cost  per  day $101 . 76 


As  to  furnace  conditions,  the  firemen  judge  by  the  C(X  recorder, 
by  the  amount  of  air  pressure  necessary  for  any  given  boiler  load, 
and  by  no  means  least  of  all  by  the  color  of  the  gases  as  they  tumble 
over  the  first  baffle  and  enter  the  top  of  the  superheater  pass.  Obser- 
vation of  the  furnace  gases,  as  they  enter  the  superheater  pass  from 
the  top  of  the  combustion  chamber,  shows  that  the  combustion  of 
volatile  gases  is  entirely  complete  and  that  the  operation  is  conse- 
quently smokeless.  At  the  same  time,  the  C02  charts  show  remark- 
ably good  results,  15%  of  C02  being  very  common,  the  average 
being  about  13.5  to  14%.  Repeated  analyses  made  with  an  Orsat 
apparatus  check  these  recording  machines  and  at  the  same  time  dis- 
cover no  more  than  from  a  trace  to  0.2%  of  carbon  monoxide. 


640  STEAM-BOILER  ECONOMY. 

Limitations  of  Boilers  as  at  Present  Installed — Furnace  Height. 
As  at  present  installed,  these  boilers  present  certain  limitations  to 
being  driven  at  any  considerably  higher  per  cent  of  rating  than  that 
already  obtained.  First,  in  burning  West  Virginia  long-flaming  bi- 
tuminous coal,  it  is  probable  that  at,  say,  275%  of  rating  and  per- 
haps somewhat  lower  than  that,  the  flames  will  reach  the  top  of  the 
combustion  chamber,  which  is  28  feet  high.  As  soon  as  uncombined 
combustible  gases  get  over  into  the  superheater  pass,  the  over-all 
efficiency  of  the  unit  will  drop,  for  although  secondary  combustion 
will  take  place,  nevertheless  some  unburned  volatile  matter  must 
escape.*  Smoking  will  begin  immediately  after  the  secondary  com- 
bustion becomes  very  considerable.  Another  limitation  is  the  drop 
in  pressure  through  the  superheater,  the  automatic  check  valves  and 
stop  valve  of  the  boiler.  At  210  per  cent  of  rating  on  one  boiler,  the 
drop  in  pressure  through  the  superheater  is  21  Ib.  which  includes  the 
pressure  drop  through  the  automatic  check  valves,  but  not  that  through 
the  main  stop  valve.  At  255  per  cent  of  rating  it  would  be  considera- 
bly more. 

The  experience  at  Delray  with  very  high  steam  velocities  has 
proved  that  in  mains  designed  especially  for  high  velocities,  such 
practice  is  very  good,  the  difficulties  being  more  than  compensated  for 
by  the  reliability,  reduced  cost  and  ease  of  maintenance  of  the  smaller 
diameters  of  mains  and  fittings. 

Effect  on  Tubes. — As  for  the  effect  on  the  front  tubes  of  the 
type-W  boiler,  of  running  at  very  high  rates  of  evaporation  it  has 
been  found  that  the  tubes  have  shown  no  evidence  of  injury  due  to 
the  hard  driving.  One  thing  is  certain,  however,  and  that  is  these 
tubes  must  be  kept  clean.  Scale  which  ordinarily  would  give  no 
trouble,  has  possibilities  for  mischief  under  the  conditions  of  harder 
driving. 

The  general  conclusions  arrived  at  from  the  experience  had  in 
operating  these  boilers,  is  that  large  units  present  possibilities  of 
economy  of  operation  and  simplicity  of  power  plant  design,  which  are 
greatly  in  advance  of  present  steam  generating  practice. 

Tests  of  Riley  Underfeed  Stokers. — On  page  641  are  the  principal 
results  of  three  8-hour  tests  of  a  625  H.P.  Babcock  &  Wilcox  boiler 
provided  with  an  8-retort  Riley  self-dumping  underfeed  stoker,  at 
the  Yonkers  power  plant  of  the  N.  Y.  Central  &  Hudson  River  R.  R., 
December,  1913. 

*  It  is  probable  that  the  flame  could  be  shortened  by  the  admission  of  a  little 
more  air,  either  through  the  stoker  or  just  above  the  bed  of  coal.  If  jets  of 
hot  air,  at  high  velocity,  so  that  they  would  travel  clear  across  the  furnace, 
were  blown  on  or  over  the  fire  bed,  a  much  shorter  flame  would  result.  The 
cause  of  long  flame  is  imperfect  mixture  of  combustible  gases  with  the  air 
required  to  burn  them.  Anything  that  will  facilitate  the  mixture  will  shorten 
the  flame.  The  excess  air  supply  might  reduce  the  efficiency  to  some  extent, 
but  this  eculd  be  tolerated  in  times  of  emergency  overloads. — W.  K. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


641 


Rating  developed Per  cent 

Blast  under  grates Ins. 

Draft  over  fire 

Uptake  temp F 

Superheat F 

B.T.U.  dry  coal 

' '       combustible 

Volatile  matter,  per  cent  of  combustible Per  cent 

Moisture  in  coal 

Ash  in  dry  coal 

Sulphur  in  dry  coal 

Combustible  in  refuse 

Water  evap.  per  sq.ft.  H.S.  per  hour Lbs. 

Effy.  boiler  and  grate Per  cent 

Uptake  gas  analysis:  Carbon  dioxide 

Oxygen 

Carbon  monoxide 


103.2 
1.6 
0.11 
401. 
93.5 
13,963 
15,705 
26.8 
2.5 
11.09 
2.58 
16.22 
3.56 
77.40 
10.7 
7.65 
0.03 


156. 
2.69 
0.11 
466.6 
122.2 
14,209 
15,408 
26.4 
5.5 
7.79 
1.19 
20.65 
5.38 
77.30 
12.0 
6.02 
0.02 


203.2 
3.52 
0.08 
490. 
141.4 
14,320 
15,624 
26.0 
2.50 
8.99 
1.89 
23.23 
7.01 
76.80 
10.9 
7.44 
0.02 


The  formula  for  maximum  results,  #=81  —  1.3(TF/*S— 3).  gives  for  the 

rates  of  driving  in  these  tests,  #  =  80.3  77.9  75.8 

The  results  obtained  were. .  .  77 . 4  77 . 3  76 . 8 


Difference. .  .  -2.9 


-0.6 


+1.0 


High  Rates  of  Driving  in  Steam  Fire-engine  Boilers.  (Eng. 
News,  March  28,  1895). — Tests  of  eleven  engines  in  Boston  gave  the 
following  results: 

Coal  per  square  foot  of  grate  per  hour,  Ibs 91.1    to    208 . 0 

Water  per  sq.ft.  of  heating  surface  per  hour,  Ibs 11 . 13  to      28 . 57 

Water  evap.  from  and  at  212°  per  Ib.  coal 2 . 26  to        5 . 87 

Heating  surface,  square  feet 74 . 0    to    229 

Water  evaporated  per  hour,  pounds 1630       to  3524 

Eight  out  of  the  eleven  engines  gave  an  evaporation  of  more  than 
20  Ibs.  per  sq.  ft.  of  heating  surface  per  hour. 

Variation  in  Gas  Analyses. — The  accompanying  cuts,  from  an 
article  by  A.  Bement,  in  Power,  Mar.  25,  1913,  show  the  different 
shapes  of  C02  diagrams  that  may  be  obtained  under  different  firing 
conditions.  No.  1  shows  a  decrease  of  C02  from  7  to  4%  in  seven 
minutes  with  a  dirty  fire,  then  a  rise  to  13%,  after  the  fire  was  cleaned. 
No.  2  shows  the  fluctuations  that  are  common  with  hand  firing.  No. 
3  shows  low  C02  due  to  holes  in  the  fire  bed  followed  by  high  C02 
after  the  fire  .was  leveled  to  close  the  holes,,  decreasing  as  the  fire 
burned  thin.  No.  4  shows  the  results  obtained  from  two  different 
firemen.  No.  5  shows  two  kinds  of  diagrams  obtained  with  a  Hawley 
down-draft  furnace  with  different  methods  of  manipulation.  In  B, 


642 


STEAM-BOILER  ECONOMY. 


the  CO,  rises  after  every  poking  of  the  fire  on  the  upper  grate  to 
cause  a  part  of  the  coal  to  fall  on  the  lower  grate.  When  the  coal  on 
the  lower  grate  burns  away  the  air  supply  increases  and  C02  lowers. 


a 

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Time  in  Minutea                                                                   Time  in  Minutes 

No.  1. 


No.  2. 


Per  cent  OO2 

0  tO  «»-0>OOo5£c»S 

First  Thickening  of 

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Time  in  Minutes 

No.  3. 


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Time  in  Minutes 


No.  4. 


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10      25      30     35      40     45     50      55     60 
Time  in  Minutes 


456       780 
Time  in  Minutes 


No.  5.  No.  6. 

FIG.  271. — VARIATIONS  IN  CC>2  WITH  DIFFERENT  FIRING  CONDITIONS. 

In  A,  the  C02  is  kept  at  the  unusually  high  level  of  16  (rather  too  high 
to  be  true^  indicates  an  error  in  the  apparatus)  by  frequent  poking 
of  the  coal  to  insure  always  a  sufficiently  thick  bed  on  the  lower  grate. 
No.  6  is  another  Hawley  furnace  diagram  showing  the  great  improve- 
ment due  to  thickening  of  the  bed  of  lump  coal  on  the  upper  grate. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


643 


Fig.  272  shows  two  days'  records  of  a  C02  meter.  The  first,  with 
an  excessive  air  supply,  shows  an  average  of  about  8%  C02,  the 
second  about  12.5%. 

Extreme    Fluctuations    of    Gas    Analysis    with    Heavy    Firing. 

(Eng.  Record,  Dec.  23,  1905). — Tests  were  made  to  show  the  com- 


Poor  firing,  air  supply  in  excess.  Good  firing. 

FIG.  272. — RECORDS  OF  A  C02  METER. 

position  of  the  gas  from  a  hand-fired  water-tube  boiler  when  the  coal 
(semi-bituminous  coking)  was  fired  in  large  quantities  at  intervals  of 
about  30  minutes.  The  results  are  given  in  the  following  table: 


No.  of 
Test. 

Shovels  of 
Coal 
Fired. 

Minutes 
after 
Firing. 

C02. 

O. 

CO. 

Sum. 

Loss  of 
Heat  Due 
to  CO,  %. 

1 

\  <>o  ( 

1 

12.4 

4.4 

1,1 

17.9 

5.67 

2 

>    M     i 

28 

10.7 

9.3 

0.1 

20.1 

0.54 

3 

•     ^9 

2 

14.0 

2.1 

2.0 

18.1 

8.  69 

4 

26 

16.9 

1.2 

1.3 

19.4 

5.00 

5 

on 

2 

13.7 

2.2 

2.5 

18.4 

io.es 

6 

23 

13.0 

6.4 

0.0 

19.4 

0 

7 

2 

14.0 

2.7 

1.7 

18.4 

7.52 

8 

20 

17 

11.6 

8.0 

0.0 

19.6 

0 

The  fire  was  barred  before  test  ISTo.  2 ;  leveled  to  fill  holes  and 
low  spots  1  minute  before  test  No.  4;  barred,  but  not  leveled,  5 
minutes  before  No.  6 ;  barred  but  not  leveled  6  minutes  before  No.  8. 
These  tests  show  that  C02  is  not  as  good  a  criterion  of  furnace  con- 
ditions as  0  is;  for  C02  13  to  14  is  coincident  with  CO  ranging  all 
the  way  from  0  to  2.5,  the  first  being  a  nearly  ideal  and  the  second  an 


644 


STEAM-BOILER  ECONOMY. 


exceedingly  bad  condition,  and  16.9  C02  is  coincident  with  1.3  CO, 
also  a  bad  condition.  With  0  6.4  the  conditions  are  almost  ideal, 
C02  13.0,  CO,  0,  but  with  0  8  or  above,  C02  is  always  low,  the  high 
0  and  the  low  C02  both  indicating  excessive  air  supply.  The  figures 
in  the  last  column  represent  the  loss  of  heat  due  to  burning  C  to  CO 

r\r\          >j- 

instead  of  C02,  calculated  by  the  formula.    Loss,  %  =  69.5 


Relation  of  C02,  0,  and  CO  in  94  Tests.—  The  following  table  is 
made  from  figures  selected  from  tables  given  by  E.  A.  Uehling  in  Jour. 
A.  S.  M.  E.,  Nov.,  1910.  All  the  analyses  showing  14  C02  or  upward 
are  given. 


Oxygen,  Per  cent. 


1-1.5 

1.6-2 

2.1-2.5 

2.6-3 

3.1-3.5 

3.6-4 

4.1-4.5 

4.6-5 

5  .  1-5  .  5 

5.5-6 

C02. 
14.0 
14.1 
14.2 
14.3 
14.4 

'  14.5  ' 
'  14.6  ' 
'  14'.  7 

'  14.8 
15.0 

Carb 
1.1 

on  Monc 

xide. 

0.2 

.  „  .  . 

0 
0 
0 
0 
0 
0 
0 
0 

0 
0 

0.7 
"0.5    ' 

'  'o.'s'  ' 

"0.2" 
0.1 
0.1 

0.8 

'.'.'.  ;:; 

0  7 

1.0 



1.0 
0.8 
0.9 
0.6 
0.9 

0.9 

0.5 

0.7 

0.1 



....... 

"o.s" 

0.8 

"0.5" 
'O.S" 

"o.'s" 
"0.2'  ' 

0.2 

"6"  ' 

.  „.  .. 

0 
0 

"6.'<J" 
0.5 
0.6 

"O.Q" 

0.5 
0.8 
0  5 



'  15.  V  ' 
'  15.2  ' 
'  15.3  ' 

'  15.4  ' 
15.5 



0.5 
0  5 

0 

0 

0.5 
0  4 

0 

0.6 
0  5 

0.4 

0 

"o.'s" 

0.5 

0.3 
0  2 

0 

"6 

0 
0 

"6" 

'6.'  s" 
"0.5" 
"o.s" 

0.4 

'6!i'  ' 

0.3 

6  '.  5 
0.3 

6!s  ' 
"6 

15.6 
15.7 
15.8 
15.9 
16.0 

"6 

0 
0 
0 

0.6 

16.1 
16.2 
16.3 
16.4 
16.5 
16.6 

Av. 

0.2 

0 

0 

0.3 
0.4 

0.2 
0.2 

"6 

0 

0.64 

0.61 

0.55 

0.36 

0.12 

0.09 

0.06 

0 

0 

0 

*  The  formula  is  derived  as  follows :  Since  the  same  volume  of  gas  is  formed 
by  burning  1  Ib.  C  to  CO  as  by  burning  it  to  CO2,  the  fraction  of  the  volumes, 
CO-r-CO+CO2  equals  the  fraction  of  1  Ib.  that  is  burned  to  CO.  As  1  Ib.  of 
C  burned  to  CO2  generates  14,600  B.T.U.,  but  only  4450  B.T.U.  when  burned 
to  CO,  the  difference,  or  loss,  of  10,150  B.T.U.  is  69.5%  of  14,600. 


RESULTS  OF  STEAM-BOILER  TRIALS.  645 

RELATION    OF    CO    TO    CO2. 

No.  of  Tests.               CO2.  CO.  Av.  CO. 

36  14      to  14.8  0  to  1.1  0.37 

34  15      to  15. 5  0  to  0.9  0.33 

13  15. 6  to  16  0  to  0.8  0.33 

10  16.1tol6.6  OtoO.4  0.13 

RELATION    OF    CO    TO    O. 

Heat  Loss  Due 

No.  of  Tests.  O.  Av.  CO2.  Av.  CO.  CO. 

54  Ito3  15.2  0.55  2.47% 

40  3  to  6  14.9  0.006  0.03% 

This  shows  that  0  is  a  more  reliable  index  of  furnace  conditions 
than  C02.  With  C02  from  14  to  16  CO  may  be  anywhere  between 
0  and  1.1%,  while  with  0  between  3  and  6  there  are  only  two  tests 
out  of  40  in  which  CO  exceeded  0.3%.  With  0  above  4  only  2  tests 
out  of  22  had  CO  as  high  as  0.2%. 

Air  Leaks  through  Boiler  Settings.  A.  A.  Gary,  Iron  Age.  Oct. 
10,  1912. — Analyses  of  the  gases  in  the  furnace  and  in  the  flue 
of  two  horizontal  tubular  boilers  and  one  water-tube  boiler  showed 
the  following  results : 

No.  1.  No.  2.  No.  3. 

Excess  air  in  the  furnace,  per  cent 70  49              45 

Excess  air  in  the  flue 103  71              96 

Temperature  of  flue  gases,  degrees  F 543  482 

Calculated   temperature  if  there  had  been 

no  air  leakage  between  furnace  and  flue  607  561 

The  analyses  of  the  gases  in  No.  3  water-tube  boiler  showed, 
furnace  C02,  12.71;  0,  6.62;  flue,  C02,  9.05;  0,  10.42.  These 
analyses  were  made  under  natural  draft  conditions.  With  forced 
draft  no  inward  air  leakage  was  found,  but  on  the  contrary  a  slight 
outward  leakage  of  gas. 

Tests  of  Washed  Grades  of  Illinois  Coal. — A  report  of  an  ex- 
tensive series  of  58  boiler  trials  with  washed  coal  and  six  trials  with 
unwashed  coal,  by  C.  S.  McGovney,  is  printed  in  Bulletin  No.  45  of 
the  University  of  Illinois  Engineering  Experiment  Station,  1909.  A 
210  H.P.  Heine  boiler  with  a  Green  traveling  chain  grate  was  used 
for  the  tests.  The  fire  brick  furnace  extended  4  ft.  in  front  of  the 
inside  of  the  front  of  the  boiler  setting,  and  the  combustion  chamber 
was  roofed  over  with  fire  brick  supported  by  the  lower  row  of  boiler 
tubes  for  a  distance  of  13  ft.  from  the  front  wall.  The  conditions 
were  thus  favorable  for  complete  combustion  of  the  volatile  matter 
of  the  coal  and  the  suppression  of  smoke.  The  figures  in  the  follow- 
ing table  are  selected  from  the  records  of  the  tests  of  washed  coal  in 
which  especial  care  was  taken  to  keep  the  furnace  conditions  uni- 
formly good  by  regulating  the  thickness  of  the  fire,  and  leveling 
it  frequently  so  as  to  avoid  the  formation  of  air  holes.  Where  two 


646 


STEAM-BOILER  ECONOMY. 


figures  appear  separated  by  a  hyphen  they  represent  the  extreme 
range  of  results  obtained  in  a  series  of  from  four  to  eight  tests.  The 
other  figures  are  averages.  The  coal,  from  three  washers  in  Ver- 
million  and  Williamson  counties,  was  of  fairly  uniform  quality,  rang- 
ing from  14,035  to  14,416  B.T.U.  per  pound  of  combustible,  and  the 
principal  difference  was  in  the  .size  of  the  several  grades,  as  shown 
in  the  table. 


Reference  No  

1 

2 

3 

4 

5 

Size  of  coal,  in  

l^tol 

1  to% 

ystoys 

^toO 

MtoO 

Aloisturc  *% 

8  06-11  .43 

8.90-10   12 

16  48-22  63 

21  .25-21  .72 

13.94-21   49 

Ash  in  dry  coal,  %  

11  '.  07-12.  80 

9.70-12i66 

8.  '.88-  U.  75 

14!40-16!l5 

10!03-15!69 

B.T.U.  perlb.  combustible.  . 

14,416 

14,395 

14,121 

14,035 

14,135 

Volatile  matter,  %  of  comb  . 

38.61 

37.54 

43.90 

44.46 

37.59 

Lbs.  comb,  per  sq.ft.  grate 

per  hr 

17.9-20.1 

15.9-30.10 

12.33-25.79 

16  81-21   70 

13  27-17  28 

H.P.  per  sq.ft.  of  grate  

5.36-5.95 

4  .  83-8  .  42 

3  .  84-7  .  73 

4'.  29-5.  51 

3.  '.02-4.  59 

H.P.  per  cent  of  rating  

97.4-108.2 

88-153 

69.9-140.5 

78-100.2 

55-83.6 

Water    evap.    from    and    at 

212°  per  sq.ft.  H.S.  perhr. 

3  .  48-3  .  86 

3.60-5.47 

3.11-5.02 

2.79-3.58 

1.96-2.98 

Efficiency  of  boiler  

66.1-68.2 

65.5-71.5 

70.1-72.9 

59.7-61.0 

52.8-60.7 

Efficiency  including  grate..  . 

64.1-65.4 

64.2-70.5 

69.2-71.6 

55.9-57.3 

48.9-58.6 

CO2  in  flue  gas,  %  

9.6-12.4 

10.27-11.48 

10.93-12.55 

6.16-6.90 

4.6-6.2 

Excess  air  flue  gas,  %  avge.  . 

81.8 

51.8 

54.3 

135.9 

169.5 

Lbs.  air  per  Ib.  comb.  avge.. 

21.05 

17.93 

17.30 

28.05 

31.56 

Temp,  of  flue  gases  °  F  
Draft    required    to    develop 

608-648 

565-748 

489-667 

581-624 

556-607 

rated  H.P.,  in.  of  water.  . 

0.32 

0.23 

0.24 

0.89 

0.83* 

*  Only  83.6%  of  rating  was  developed  with  this  draft. 

The  highest  efficiency  in  the  whole  series,  72.95%,  was  obtained 
with  the  %-  to  %-in.  coal  when  the  boiler  was  driven  at  139.6% 
of  rating.  The  C02  in  the  flue  gases  was  12.55%'  and  their  tem- 
perature the  lowest  in  the  whole  series,  489°  F.,  Tbo  moisture 
in  the  coal  in  this  test  was  19.49%.  Eight  tests  were  made  with  this 
coal,  and  the  results  are  all  relatively  high.  Another  set  of  five  tests 
was  made  with  the  same  coal  when  no  especial  precautions  were 
taken  to  keep, the  fire  in  the  best  condition,  and  the  boiler  efficiency 
was  only  62.8-66.8%,  and  the  "over  all"  efficiency,  including  boiler 
and  grate  58.2-64.0%.  The  average  "over  all"  efficiency  of  the 
eight  tests  was  70.1%  and  of  the  five  tests  61.9%,  showing  a  saving 
of  fuel  due  to  proper  control  of  the  fire  of  8.2  -7-  -70.1  =  11.7%. 

In  the  tests  with  the  small  sizes  of  coal  it  was  not  found  possible  to 
control  the  furnace  conditions  so  as  to  develop  the  rated  capacity 
of  the  boiler  without  making  holes  through  the  fire,  causing  a  great 
excess  of  air  to  pass  into  the  furnace,  which  retarded  the  rate  of 
combustion.  It  is  evident  that  much  is  jet  to  be  learned  in  regard 
to  the  best  method  of  burning  the  finest  sizes  of  coal. 

It  is  to  be  noted  that  these  tests  were  made  under  far  better  con- 
ditions than  are  usually  obtainable,  and  the  results  are  much  higher 
than  thosje  obtained  in  common  practice. 

Tests  with  North  Dakota  Lignite,  made  by  D.  T.  Randall  and 
Henry  Kreisinger,  are  reported  in  Bulletin  2  of  the  Bureau  of  Mines, 
1910.  This  lignite  is  difficult  to  burn  in  ordinary  boiler  furnaces, 


RESULTS  OF  STEAM-BOILER  TRIALS.  647 

but  the  tests  have  shown  the  possibility  of  designing  suitable  furnaces 
for  burning  it  profitably.  In  these  tests  a  Stirling  boiler  and  a  furnace 
consisting  of  a  Dutch  oven  and  an  arch  with  downwardly  inclined 
roof,  extending  about  5  ft.  beyond  the  grate  bars,  were  used.  The 
lower  edge  of  the  fire  door  was  21  ins.  above  the  level  of  the  rocking 
grate.  The  furnace  was  designed  to  run  on  the  gas  producer  principle. 
Air  for  the  combustion  of  the  gases,  preheated  in  coils  from  .200°  to 
300°  F.  was  introduced,  at  a  pressure  of  0.5  to  1  in.  of  water/ through 
numerous  small  openings  in  the  bridge  wall.  Additional  air  was 
admitted  through  openings  over  the  fire  from  an  air  space  in  the 
double  roof  of  the  Dutch  oven.  The  air  supply  under  the  grates 
was  furnished  by  Argand  steam  blowers.  With  rates  of  combustion 
exceeding  25  Ibs.  of  fuel  per  sq.  ft.  of  grate  per  hour  the  flame 
extended  into  the  space  in  front  of  and  above  the  arch.  At  the  close 
of  each  test  a  quantity  of  clinker  amounting  to  several  hundred 
pounds  was  found  on  the  grate,  not  being  removed  by  the  operation 
of  rocking  the  grate  bars.  The  tests  were  made  with  running  start 
and  stop,  a  correction  for  the  clinker  being  made  by  stopping  the  tests 
with  tne  fuel  bed  3  or  4  ins.  higher  than  at  the  start.  The  error 
of  the  weight  of  the  fuel  consumed  was  estimated  as  possibly  1V2% 
too  high  or  too  low.  Fifteen  tests  in  all  were  made,  and  the  two 
given  in  the  following  table  represent  the  extreme  range  of  the  rates  of 
combustion : 

TESTS   WITH    NORTH   DAKOTA    BROWN   LIGNITE. 

Test  No 4  11 

Duration  of  test. .. Hrs.  14.75  10.03 

Dry  fuel  per  sq.  ft.  grate  per  hour Lbs.  19 . 52  29 . 43 

Refuse  in  dry  fuel Per  cent  14.08  12.49 

Moisture  in  fuel  as  fired 44 . 26  42 . 88 

Volatile  matter  in  combustible ' '  50 . 52  49 . 24 

Sulphur  in  dry  fuel 1 .42  1 .68 

Water  evaporated  from  and  at  212°  per  hour: 

per  Ib.  fuel  as  fired Lbs.  3 . 36  3 . 48 

per  Ib.  dry  fuel "  6.02  6.10 

per  Ib.  combustible 7.34  7.48 

Horse-power  developed,  per  cent  of  rating Per  cent  73.9  112.8 

Efficiency  of  boiler  and  furnace "  61 .2  62.5 

including  grate "  57.7  59.2 

over  all,  deducting  steam  used  by  blower. .  52.6  54.5 

Temperature  of  flue  gases Deg.  F.  436  570 

Gas  analysis,  CO2 9.79  10.92 

0 9.27  8.26 

CO 0.05  0.23 

Loss  due  to  imperfect  combustion,  radiation,  and  un- 
accounted for Per  cent  11 . 78  5 . 78 

NOTES. — The  visible  smoke  during  all  the  tests  was  very  light  and  appeared 
to  consist  mostly  of  water  vapor.  Superheated  steam  was  used  in  the  ash 
pit  blowers  (Argand).  Test  No.  11  represented  the  highest  capacity  that, 
could  be  developed  with  the  apparatus  without  great  decrease  of  efficiency. 
The  boiler  was  rated  at  258  horse-power.  Heating  surface  2587  sq.ft.,  grate 
surface,  54  sq.  ft.,  ratio  46  to  1.  It  is  evident  that  the  capacity  might  have 
been  much  greater  if  the  grate  surface  had  been  larger.  A  curve  of  the  15 


648  STEAM-BOILER  ECONOMY. 

tests  shows  that  the  efficiency  of  boiler  and  furnace  drops  from  about  63  to 
57%  as  the  rate  of  combustion  increases  from  19  to  29  Ibs.  per  sq.  ft.  of  grate 
per  hour.  This  drop  is  perhaps  mostly  due  to  less  complete  combustion  of 
the  gaseous  combustible  in  the  combustion  space  of  the  boiler. 

The  results,  says  the  Bulletin,  show  that  this  combination  of  boiler  and 
furnace  gives  good  results  with  North  Dakota  lignite.  A  fuel  efficiency  (over 
all)  of  from  55  to  58%  can  be  obtained  with  the  full  capacity  of  the  boiler. 
The  steam  blower  for  the  ash  pit  is  inefficient,  and  there  is  no  gain  in  supplying 
superheated  steam  to  it.  A  considerable  saving  could  probably  be  made  by 
substituting  a  fan  such  as  is  commonly  used  for  forced  draft. 

Tests  with  Coke-oven  and  Blast-furnace  Gas  are  reported  in  Stahl 
und  Eisen,  Aug.  1913,  Jour.  A.  S.  M.  E.,  Oct.  1913.  A  double  flue 
boiler  of  925  sq.  ft.  heating  surface,  fired  with  coke-oven  gas,  and  driven 
at  the  rate  of  2.4  and  2.6  Ibs.  per  sq.  ft.  heating  surface  per  hour,  gave 
74.9  and  80.2%  as  the  combined  efficiency  of  boiler,  superheater  and 
economizer.  A  similar  boiler  with  968  sq.  ft.  heating  surface  and  602 
sq.  ft.  superheater  surface  fired  with  blast  furnace  gas  in  three  tests 
gave  efficiencies  as  follows:  boiler  64.5;  61;  63;  superheater,  9.7;  7.8; 
10.3;  economizers  5.2;  8.0;  9.4;  total,  79.4;  76.8;  82.7.  The  rates 
of  driving  in  Ibs.  water  evaporated  from  and  at  212°  per  sq.  ft.  heating 
surface  per  hour  were  respectively  3.45;  2.91;  3.14.  The  composition 
of  the  gas  used  in  the  three  tests  was :  C02,  12.4 ;  11.4 ;  11.4 ;  CO,  26.6 ; 
27.4;  27.4;  H,  4.8;  4.2;  4.0;  N,  56.2;  57.0;  57.2.  The  chimney  gases 
analyzed :  C02,  23.4 ;  24.1,  23.3 ;  0,  0 ;  0.8 ;  1.0 ;  CO,  3.4 ;  0 ;  0.2".  The 
fuel  gases  in  these  tests  were  accurately  measured  by  a  gasometer. 

The  Hohenstein  Boiler,  whicb  was  used  by  the  U.  S.  Liquid 
Fuel  Board  in  experiments  with  oil  as  fuel,  is  shown  in  Fig.  273. 
The  lower  row  of  tubes,  which  support  the  fire-brick  roof  of  the 
furnace  are  4  in.  diameter;  all  the  other  tubes,  which  are  arranged  in 
banks  inclined  in  opposite  directions,  are  2  in.  The  dimensions  of 
the  experimental  boiler  are  as  follows:  Front  and  rear  steam  drums, 
24  in.;  four  connecting  drums,  each  16  in.;  mud  drum,  24  in.; 
tubes,  sixteen  4-in.,  7  ft.  long,  384  2-in.  9  ft.  long,  and  15  5-in.  down- 
take  tubes.  Heating  surface,  2130  sq.  ft.;  grate  surface  50.1  sq.  ft. 
Floor  space  9  ft.  wide;  11  ft.  deep;  height  12  ft.  7  in.  Weight, 
boiler  and  fittings,  witb  water,  54,127  Ibs.,  without  water,  46,668 
Ibs.  Weight  with  water  at  275  Ibs.  pressure,  per  sq.  ft.  of  grate 
surface,  1080  Ibs.;  per  sq.  ft.  beating  surface  25.4  Ibs.  Air  spaces 
in  grate,  57%  of  grate  area.  Height  of  smoke  stack  above  grate, 
70  ft. ;  cross-section  of  smoke  stack,  8.7  sq.  ft.  The  boiler  was  driven, 
witb  oil  as  fuel,  at  a  rate  of  evaporation  as  high  as  16.7  Ibs.  of  water 
per  sq.  ft.  of  beating  surface  per  hour.  The  low  efficiencies  shown  in 
the  table  below  were  no  doubt  due  to  the  combustion  chamber  being 
far  to  small  to  allow  complete  combusion  of  the  gases.  At  times  of 
rapid  driving  great  volumes  of  dense  smoke  were  emitted  from  the 


RESULTS  OF  STEAM-BOILER   TRIALS. 


649 


chimney.  The  lesson  to  be  learned  from  these  tests  is  that  very  low 
efficiency  may  be  obtained  with  fuel  oil  when  it  is  burned  imperfectly. 
These  tests  may  be  compared  with  those  of  the  Yarrow  boiler,  given 


FIG.  273.— THE  HOHENSTEIN  BOILER. 

below,  to  show  the  great  improvement  made  in  oil-burning  in  recent 
practice. 

Comparative  Tests  with  Oil  Fuels.  Edgar  Kidwell  (Power, 
May  19,  1908)  gives  a  table  of  results  of  four  tests  with  a  Babcock 
&  Wilcox  boiler  and  four  with  a  Stirling  boiler,  both  using  Cali- 
fornia oil  of  the  same  quality,  18,500  to  18,750  B.T.U.  per  lb.,  cor- 
rected for  moisture,  from  which  the  following  figures  are  taken : 

Water  evaporated  from  and  at  212°  per  square  foot  per  heating  surface  per  hour. 

B.  &W !     3.85    ....   I     4.52|    ....   |     5.86|   ....   |     7.11 

Stirling 3 . 58 


4.551    .. 
Efficiency. 


5.68 


6.94 


B.  &  W      

83.06 

80.64 

79.37 

73.62 

Stirling  

79.'  16 

76  .'73 

74.'  05 

7i!50 

Temp,  flue  gases.  .  .  . 

454 

438" 

517 

464 

606 

525" 

720 

622" 

Effy.  compared  with 

formula  

-3.09 

+  1.17 

-4.25 

-0.38 

-5.47 

+0.09 

-6.38 

-4.04 

650  STEAM-BOILER  ECONOMY. 

TESTS    OF   THE    HOHENSTEIN   EXPERIMENTAL   MARINE    BOILER. 

Engineering  News,  April  9,  1903. 


COAL   TRIALS. 


Water  per  sq.ft.  heating  surface  per  hr.  .  . 
Coal  per  sq  ft  ,  grate,  per  hr 

3.84 
18  5 

4.75 
22  9 

5.50 

28  8 

7.23 
35  5 

10.12 
53  4 

12.18 

72  2 

Equiv  evap  per  Ib.  combustible. 

11  77 

11  59 

11  69 

11  41 

10  79 

9  53 

Stack  temperature  less  fire  room  temp.  °  F. 
Loss  in  heat  up  stack,  |per  cent  
Loss  in  heat  due  to  incomplete  combustion 
of  C  per  cent  

396 

481 
17.7 

5  9 

475 

572 
15.9 

10  4 

631 

866 
28.3 

3  4 

Boiler  efficiency,  per  cent  .  . 

73.4 

72.3 

73 

72.8 

67.2 

59.4 

OIL   TRIALS. 


Water  per  sq.ft  heating  surface 
per  hr 

4  57 

5  50 

5  61 

8  19 

9  23 

11  38 

13  86 

14  55 

Equiv.  evap.  per  Ib.  of  oil  
Stack    temperature    less    fire- 
room  temp 

14.43 
397 

14.22 
445 

14.35 
479 

13.29 
627 

12.70 
584 

12.18 
657 

11.73 
746 

10.77 
902 

Loss  in  heat  up  stack,  per  cent  . 
Loss  in  heat  due  to  incomplete 
combustion  of  C 

13.2 
2  4 

14.4 

0  7 

15.4 
0  4 

15.1 
1  2 

17.3 

7  7 

20.1 
6  4 

24.2 
1  7 

28.1 

1  2 

Boiler  efficiency 

71  5 

70  4 

71  1 

65  8 

62  8 

60  3 

58  1 

53  4 

The  formula  used  for  comparison  is  #=83  —  l.3(W/S—3) 
which  is  taken  to  be  that  of  best  probable  performance  for  oil 
under  the  most  favorable  conditions.  The  explanation  of  the  better 
performance  of  the  B.  &  W.  boiler  as  compared  with  that  of  the 
Stirling  is  that  the  furnaces  were  different.  The  Babcock  &  Wilcox 
boiler  was  equipped  with  a  furnace  having  burners  located  at  the 
bridgewall,  and  discharging  the  flame  toward  the  front  of  the  boiler. 
The  Stirling  boiler  was  equipped  with  burners  inserted  through 
the  fire-doors  and  directing  flame  toward  the  bridgewall  in  accordance 
with  the  usual  practice.  The  large  drop  in  efficiency  of  the  B.  &  W. 
boiler  at  the  highest  rate  of  driving  is  probably  due  to  an  insufficient 
furnace  volume  for  burning  the  oil  at'  that  rate.  The  higher  tem- 
peratures of  the  flue  gases  in  the  Stirling  tests  indicates  that  the 
combustion  of  the  gases  from  the  oil  was  not  completed  in  the 
furnace. 

Tests  of  a  Boiler  with  Oil  Fuel  at  Redondo,  Cal.  (Power,  May  9, 
1911).— The  boiler  was  a  Babcock  &  Wilcox,  3-pass,  with  6042  sq. 
ft.  water  heating  surface  and  960  sq.  ft.  superheating  surface.  Ham- 
mel  oil-burners  were  used,  steam-driven,  and  supplied  with  air  which 
was  heated  in  brick  tunnels  under  the  furnace.  The  principal  results 
were  as  follows,  the  tests  being  arranged  in  the  order  of  the  rate  of 


RESULTS  OF  STEAM-BOILER  TRIALS. 


651 


driving:  (There  were  seven  tests.    No.  5  in  the  table  gives  the  average 
results.    See  Trans.  A.  8.  M.  E.,  1911,  p.  90.) 


No 

1 

2 

3 

4 

5 

6 

7 

8 

Per  cent  of  rating 

72  7 

94  0 

109  2 

109.4 

125  3 

132  8 

163  3 

195  5 

Water*  per  Ib.  oil  
Flue  gas  temp 

15.35 

385 

15.66 
397 

15.75 
406 

15.47 
409 

15.15 
434 

15.37 
429 

14.37 

477 

14.12 
537 

12  2 

13  4 

14  3 

13  3 

13  2 

14  2 

13  3 

12  1 

O  in  gases  
Excess  air,  per  cent  
B.T.U.  per  Ib.  oil  

3.6 

28.7 
18,280 

2.7 
17.7 
18,256 

1.8 
10.6 
18,253 

2.4 
18.5 
18,131 

3.1 
21.2 
18,184 

1.7 
11.3 

18,214 

2.8 
18.5 
18,171 

6.8 
43.0 
17,985 

Density,  Baume  

13.3 
0  4 

13.3 
0  5 

13.3 
0  4 

13.4 
0  45 

13.2 
0  54 

13.2 
0  8 

13.2 
0  65 

12.9 
0  6 

Water*  per  sq.  ft.  H.S.  per  hr.  .  .  . 
Efficiency,  per  cent  
Steam  used  by  burners,  per  cent 
of  total  steam. 

2.54 
81.1 

1  54 

3.24 

82.8 

2  25 

3.77 
83.3 

2  40 

3.78 
82.4 

2  40 

4.32 
80.5 

2  15 

4.58 
81.5 

2.25 

5.63 
76.4 

2  08 

6.74 
75.8 

2  13 

131 

134 

142 

134 

138 

140 

142 

142 

Efficiency  by  formula  
Actual  efficiency,  -f-  or  — 

82.7 
+0   1 

81.6 
+  1   6 

81.6 

+0  8 

80.6 
—0  1 

80.0 
+1  5 

77.9 
—  1  5 

75.7 
—0  1 

*  Evaporated  from  and  at  212°. 

The  straight-line  formula  between  tests  No.  2  and  No.  8  is 
E  =  83.2—  (W/S—  3).  The  figures  in  the  last  line  show  how 
closely  the  results  obtained  agreed  with  this  formula.  The  tests  are 
of  especial  interest  in  show- 
ing that  high  economy  can 
be  obtained  at  high  rates  of 
driving  when  the  percentage 
of  oxygen  in  the  gases  and 
the  excess  air  supply  are 
kept  low. 

The  temperature  of  the 
gases  was  taken  by  electric 
pyrometers  at  six  points  as 
shown  in  Fig.  274.  The 
results  were  as  follows  :  FIG.  274. — LOCATION  OF  PYROMETERS. 


No.  of  test     

1 

2 

3 

4 

5 

6 

7 

Av£T6 

Evap.  from  and  at  212° 
per  sq.ft.  H.S.  per  hr. 
Temperature  of  gases  : 
1.  Above  3d  tube  1st 
pass        

2.54 
1100 

3.24 
1090 

3.77 

1160 

3.78 
1180 

4.58 
1240 

5.63 
1300 

6.74 
1600 

4.32 
1240 

2.  Top  of  1st  pass.  .  .  . 
3.  Top  of  2d  pass.  .  .  . 
4.  Bottom  of  2dpass. 
5.  Bottom  of  3d  pass  . 
6.  In  flue.    .    . 

640 
570 
500 
450 
385 

640 
540 
500 
450 
398 

700 
620 
520 
505 
409 

680 
610 
510 
495 
406 

780 
650 
550 
530 
429 

940 
740 
600 
570 

477 

1170 
820 
700 
660 
538 

793 
650 
554 
523 
435 

Temp,    of    superheated 
steam 

473 

457 

468 

465 

474 

494 

527 

480 

Degrees  of  superheat.  .  . 

92 

76 

87 

84 

93 

113 

144 

98 

652 


STEAM-BOILER  ECONOMY. 


Tests  of  a  Marine  Boiler  with  Oil  Fuel . — A  series  of  six  tests  of  a 
Babcock  &  Wilcox  marine  boiler  with  Texas  crude  oil  at  rates  of  driv- 
ing from  4.11  to  15.83  Ibs.  evaporated  from  and  at  212°  per  sq.  ft. 
of  heating  surface  per  hour  is  reported  in  Jour.  Am.  Soc.  Naval 
Engineers,  May,  1911.  Peabody  mechanical  atomizers  were  used. 
The  heating  surface  of  the  boiler  was  2571  sq.  ft.,  volume  of  furnace 
217  cu.  ft.  Following  are  the  principal  results: 

OIL   TESTS    OF   BABCOCK    &    WILCOX   MARINE    BOILER. 


Number  of  test.         

1 

2 

3 

4 

5 

6 

Number  of  burners  in  use  .... 

11 

8 

4 

3 

8 

8 

Steam  pressure  by  gage,  Ibs.  .  . 
Oil  pressure  by  gage,  Ibs 

209.9 
191  1 

210.4 

188.8 

210.7 
175.6 

212 
131  3 

214.8 
153  2 

214.8 
171  8 

Temp,  of  fireroom,  degrees  F  . 
Temp  of  oil  degrees  F. 

71.1 
175.3 

75.2 
183  4 

70 

184  0 

79 
210  1 

79 
199  0 

76 

195  7 

Temp,  of  chim.  gases,  deg.  F  . 
Percent,  of  moisture  in  steam  . 
Smoke  scale  of  5          

771 
.811 
2.1 

666 
.710 
1.5 

533 
.163 
1  3 

447 
.109 
1  5 

702 
.218 
2  3 

630 
.165 
1  15 

Oil  per  hour  pounds  .  . 

2,972 

1,704 

1,202 

666 

1,922 

1  947 

Oil  per  h.  per  cu.  ft.  furnace 
volume  Ibs                 

13.69 

7.85 

5.54 

3  07 

8  86 

8  97 

Oil  per  hr.  per  sq.  ft.  heating 
surface  Ibs                     .... 

1.156 

.663 

467 

259 

747 

757 

Oil  per  hr.  per  burner,  Ibs  .... 
Equiv.    to  coal  per    sq.ft.   of 
grate  surface    Ibs 

270.2 
75.34 

213 

37.45 

300.5 
28.34 

222 
16  13 

240.3 
43.96 

243.4 
46  14 

Equiv.  evaporation  from  and 
at  212°  F.  per  sq.ft.  of  heat- 
ing surface  Ibs 

15.83 

9  53 

7.35 

4  11 

10  56 

11  69 

Equiv.  evaporation  from  and 
at  212°  F.  per  cu.ft.  of  fur- 
nace volume,  Ibs  
Evaporation  from  and  at  212° 
F.  per  Ib.  oil,  Ibs  

Chimney  Gas  Analysis 
Carbon  dioxide  (CO2)   . 

187.60 
13.70 

9  85 

112.87 
14.37 

9  26 

87.06 
15.72 

11  57 

48.70 
15.86 

11  86 

125.10 
14.12 

10  71 

138.53 
15.44 

10  94 

Oxygen  (O) 

6  46 

7  68 

4  50 

4  08 

5  18 

4  73 

Carbon  monoxide  (CO)  
Nitrogen  (N)         

.01 

83  68 

.00 
83  06 

.04 
83  89 

.04 
84  02 

.02 

84  09 

.00 

84  33 

Efficiency 
Efficiency  of  boiler  

69  29 

72  68 

79  50 

80  21 

71  41 

78  08 

The  plotted  diagram  of  these  tests,  Fig.  275,  indicates  that  the  re- 
ported efficiency  of  Nos.  3  and  6  may  be  3  or  4  per  cent  too  high,  and 
that  Nos.  2  and  5  are  lower  than  they  would  be  under  the  most 
favorable  conditions.  The  formula  of  the  straight  line  drawn  from 
No.  4  to  No.  1  is  E  =  81.24  -  0.93  (W/8  —  3). 

The  analysis  of  the  chimney  gases  in  the  best  test,  No.  4,  showed 
C02,  11.86;  0,  4.08;  CO,  0.04;  N,  84.02.  This  corresponds  to  21.05 
Ibs.  dry  gas  per  Ib.  carbon.  A  heat  balance  shows  the  following: 


RESULTS  OF  STEAM-BOILER   TRIALS. 


653 


B.T.U.  Per  cent. 

Loss  of  heat  in  the  dry  gases 21.05X368X0.24=  1,859  9.75 

Loss  of  heat  in  H2O  from  H  in  the  oil  . .  0.109  X9X  (212-79)  + 

970+0.48(447-212) =    1,193  6.26 

Utilized  in  making  steam 15.86X970.4  =  15,391  80.21 

18.443  96.22 

Loss  by  radiation,  heating  moisture  in  air,  incomplete  combus- 
tion, and  unaccounted  for 747  3 . 78 

19,190  100.00 


No. 

"*••*•„ 

^ 

•  H 

o.3 

No.6 

•x^ 

\ 

^ 

.1 

0.2 

xvv 

•  1 

0.5 

\ 

„ 

No.l 

4        5       6        7        8       9       10      11      12      13      14      15     16 
Water  evaporated  from  and  at  212°  per  sq.ft.per  hour 

FIG.  275. — RESULTS  OF  TESTS  WITH  OIL  FUEL. 

Test  of  a  Yarrow  Boiler  with  Oil  Fuel.  (Proc.  Inst.  Nav  Arch., 
1912). — A  modified  Yarrow  boiler,  in  which  some  of  the  upper  rows 
of  tubes  on  one  side  were  removed  and  an  equal  amount  of  super- 
heating surface  was  added  above  the  nest  of  tubes,  was  tested  with 
results  as  below.  The  total  heating  surface  was  6700  sq.  ft.,  of  which 
1265  sq.  ft.  was  superheating  surface.  The  steam  pressure  was  about 
242  Ibs.  The  superheating  ranged  from  21°  at  the  lowest  rate  of 
driving  to  93°  at  the  highest. 


Evaporation  from  and  at  212°,  Ibs. 
per  sq.  ft.  heating  surface  per  hr. 
Evaporation  per  Ib.  of  oil  

1.55 
16  1 

3.7 
16.1 

8.6 
15.9 

12.9 
15.2 

14.4 
15.0 

18.0 
14.6 

Lbs.  oil  per  sq.  ft.  heat.  surf,  per  hr. 
Temp,  of  gases  between  water  tube 
and  superheater  

0.096 
465 

0.230 
481 

0.5421 
647 

0.850 
903 

0.964 
926 

1.237 
1121 

Temp,  of  gases  above  superheater.  . 
above  large  nest  of 
tubes   

409 
416 

432 
448 

536 
551 

685 
688 

698 

727 

828 
887 

Efficiency   (estimated   on  basis  of 
19,500  B.T.U.  per  Ib.  of  oil)  %  .  . 

80.1 

80.1 

79.0 

75.2 

74.2 

72.6 

This  test  is  remarkable  for  the  high  rate  of  evaporation  reached 
and  for  the  small  decrease  in  efficiency  with  increased  rates  of  driving. 


654 


STEAM-BOILER  ECONOMY. 


(W       \ 
-<7-3j±  1  expresses  the  relation  of. the 

efficiency  to  rate  of  driving  when  the  latter  is  above  3  Ibs.  per  sq.  ft. 


Air  Cooled 
Damper ' 


Partition 
Plate 


Pocket 


FIG.  276.  —  YARROW  BOILER  WITH  SUPERHEATER. 

of  heating  surface  per  hour.    The  cut,  Fig.  276,  shows  the  location  of 
the  superheater  tubes. 

Tests  of  Two  Kinds  of  Tile  Roof  in  a  Heine  Boiler.     (Bulletin 

No.  34  U  of  111.  Eng.  Expt. 

1909.)—  Tests 

with    a    Heine 


Sta.,  0.—  ess  were 
made  with  a  Heine  boiler 
provided  with  a  chain  grate 
furnace  and  an  extension 
arch  built  3  ft.  in  front  of  the 
boiler.  The  setting  was  of  the 
usual  form.  The  roof  of  the 
furnace,  made  by  tiles  sup- 
ported by  the  lower  row  of 
tubes,  in  four  tests  was  of 
what  is  known  as  C-tile,  which 
completely  envelop  the  tubes, 
and  in  four  other  tests  of  T-tile,  which  rest  upon  the  tubes,  covering 
their  upper  surface  only. 

The  coal  was  Vermilion  Co.,  111.,  screenings,  averaging  12.2% 
moisture  and  14.6%  ash  by  analysis.  In  the  boiler  tests  the  ash  and 
refuse  averaged  in  the  C-tile  tests  19.80%  and  in  the  T-tile  tests 
15.75%.  The  differences  in  handling  the  fire  in  the  two  tests  as 
shown  by  the  difference  in  percentage  of  refuse  and  in  the  C02  in  the 
gases,  which  latter  is  far  too  low  for  good  economy,  go  far  to  ac- 
count for  the  difference  of  3%  in  efficiency.  With  the  C-tile  nearly 


e-tile. 
FIG.  277. — Two  K&DS  OF  TILE  ROOF. 


RESULTS  OF  STEAM-BOILER  TRIALS. 


655 


C-Tile. 

T-Tile. 

Difference. 

Temp  front  part  of  furnace 

2066 

1883 

183 

1  '       over  bridge-  wall.             .  .  . 

2151 

1851 

300 

"      forward  part  of  combustion  chamber. 
'  '      rear  part  of  combustion  chamber.  .  .  . 
in  uptake  

1968 
1642 
558 

1597 
1384 
468 

371 

258 
90 

Efficiency,     (C-tile,    64.4    to    66.3,    T-tile, 
67  5  to  69  4)  Av  of  4 

65  6 

68  6 

3 

CO2  in  flue  gases 

6  8 

7  5 

Smoke         

None 

Very  little 

Water  evap.  from  and  at  212°  per  sq.  ft.  H.  S. 
per  hr.  .  , 

3.68 

3.72 

the  whole  heating  surface  of  the  lower  row  of  tubes  was  protected 
from  impingement  by  the  hot  gases,  and  effectively  shielded  from 
radiation  from  the  fuel  bed  and  the  particles  of  incandescent  carbon 
in  the  gases. 

It  was  evident,  says  the  report,  that  had  higher  capacity  been  de- 
manded, trouble  with  black  smoke  would  have  resulted  with  the  T-tile 
roof.  In  that  case  it  is  likely  that  the  C-tile  roof  would  have  shown 
the  higher  efficiency. 

Superheated  Steam  in  Locomotive  Service. — Publication  No.  127  of 
the  Carnegie  Institution  of  Washington,  a  book  of  144  pages,  contains 
the  full  record  of  a  research  by  Dr.  W.  F.  M.  Goss,  made  in  the 
laboratory  of  Purdue  University,  of  the  operation  of  two  locomotives, 
one  with  saturated  and  the  other  with  superheated  steam.  The  results 
are  reviewed  by  Dr.  Goss  in  Bulletin  57  of  the  University  of  Illinois 
Engineering  Experiment  Station,  1912.  The  following  is  a  summary 
of  his  conclusions : 

Superheated  steam  may  be  successfully  used  in  locomotive  service 
without  involving  mechanism  which  is  unduly  complicated  or  difficult 
to  maintain. 

The  various  details  in  contact  with  the  highly  heated  steam,  such 
as  the  superheater,  piping,  valves,  pistons,  and  rod  packing,  give 
practically  no  trouble  in  maintenance. 

Superheating  materially  reduces  the  consumption  of  water  and 
fuel  and  increases  the  power  capacity  of  the  locomotive. 

The  combined  boiler  and  superheater  tested  contains  934  sq.  ft. 
of  water-heating  surface  and  193  sq.  ft.  of  superheating  surface;  it 
delivers  steam  which  is  superheated  approximately  150°.  The  amount 
of  superheat  diminishes  when  the  boiler-pressure  is  increased,  and 
increases  when  the  rate  of  evaporation  is  increased,  the  precise  relation 
being, 

T  =  123  —  0.265  P  +  7.28  H 

where  T  represents  the  superheat  in  degrees  F.,  P  the  boiler-pres- 
sure by  gage,  and  H  the  equivalent  evaporation  per  foot  of  water- 
heating  surface  per  hour. 


656  STEAM-BOILER  ECONOMY. 

The  evaporation  of  the  combined  boiler  and  superheater  tested  is 
£='11.706  —  0.2145 

where  E  is  the  equivalent  evaporation  per  pound  of  fuel  and  H  is  the 
equivalent  evaporation  per  hour  per  square  foot  of  water-heating  and 
superheating  surface.* 

The  ratio  of  the  heat  absorbed  per  square  foot  of  superheating 
surface  to  that  absorbed  per  square  foot  of  water-heating  surface  ranges 
from  0.34  to  0.53,  increasing  as  the  rate  of  evaporation  is  increased. 
•  When  the  boiler  and  superheater  are  operated  at  normal  maximum 
power,  and  when  they  are  served  with  Pennsylvania  or  West  Virginia 
coal  of  good  quality,  the  available  heat  supplied  is  accounted  for 
approximately  as  follows : 

Per  cent 

Absorbed  by  water 52 

Absorbed  by  steam  in  superheater 5 

Utilized : 57 

Lost  in  vaporizing  moisture  in  coal 5 

Lost  in  CO 1 

Lost  through  high  temperature  of  escaping  gases 14  * 

Lost  in  the  form  of  sparks  and  cinders 12 

Lost  through  grate 4 

Lost  through  radiation,  leakage,  and  unaccounted  for 7 

Neither  the  steam  nor  the  coal  consumption  is  materially  affected 
by  considerable  changes  in  boiler-pressure,  a  fact  which  justifies  the 
use  of  comparatively  low  pressures  in  connection  with  superheating. 

For  maximum  cylinder  efficiency  with  steam  superheated  150°, 
when  the  boiler-pressure  is  120,  the  best  cut-off  is  approximately  50 
per  cent  of  the  stroke,  diminishing  as  the  pressure  is  raised,  until  at 
240  Ibs.  it  becomes  20  per  cent. 

The  saving  in  water  consumption  and  in  coal  consumption  per 
unit  power  developed,  which  was  effected  by  the  superheatng  loco- 
motive, in  comparison  with  the  saturated-steam  locomotive,  is  as 
follows : 

Boiler  pressure 120  160  200  240 

Water  per  I.H.P.  hr.  saturated .  .  29 . 1  26 . 6  25 . 5  24 . 7 

"       "          "         superheated  23.8  22.3  21.6  22.6 

Gain  per  cent 18  16  15                   9 

Coal  per  I.H.P.  hr.  saturated, . .         4 . 00  3 . 59  3 . 43            3.31 

"       "         "           superheated         3.31  3.08  2.97            3.12 

Gain  per  cent 17  14  13                  6 

The  power  capacity  of  the  superheating  locomotive  is  greater  than 
that  of  the  saturated-steam  locomotive. 

*  Assuming  14,000  B.T.U.  per  pound  as  the  heating  value  of  the  fuel,  this 
formula  is  equivalent  to  Efficiency  =  77.6  —  1.5(W/S  —  3),  which  may  be  com- 
pared to  the  several  straight  line  formulaR  given  in  Chap.  IX. 


RESULTS  OF  STEAM-BOILER   TRIALS. 


657 


The  number  of  superheating  locomotives  in  Europe  is  now  (1911) 
reported  as  7000  and  that  the  number  in  this  country,  in  service 
or  under  order,  is  approximately  2000. 

Tests  of  Boilers  with  Natural  Gas  as  Fuel. — J.  M.  Whitham 
(Trans.  A.  S.  M.  E.,  1905)  reports  the  results  of  several  tests  of 
water-tube  boilers  with  natural  gas.  The  following  is  a  condensed 
statement  of  the  results: 


Kind  of  Boiler  

Cook 

Vertical. 

Heine. 

Cahall 

Vert. 

Rated  H.  P.  of  boilers.  . 
H.  P.  developed  
Temperature  at  chimney 
Gas  pressure  at  burners, 
oz    .    .  .          

1500 
1642 
521 

6  9 

1500 
1507 
494 

6  4 

200 
155 
386 

200 
218 
450 

200 

258 
465 

300 
340 
406 

4  8 

300 
260 
374 

7  to  30 

Cu.  ft.  of  gas  per  boiler 
H.  P.-hour  

44  9 

*  41  0* 

46  Of 

40  7f 

38  3f 

42.3 

34 

Boiler  efficiency,  %.  .  .  . 

72  7 

65  8 

74.9 

*  Reduced  to  4  oz.  pressure  and  62°  F. 
t  Reduced  to  atmos.  press,  and  32°  F. 

Mr.  Whitham  found  that  as  good  economy  was  obtained  with  a 
blue  as  with  a  white  or  straw  flame,  and  no  better.  Greater  capacity 
may  be  made  with  a  straw  white  than  with  a  blue  flame.  A  writer 
in  Power,  Oct.  22,  1912,  commenting  on  this  says  "it  is  generally  con- 
ceded that  the  blue  flame  indicates  more  efficient  combustion,,  a 
higher  temperature  and  a  superior  performance,  other  things  being 
equal."  Things  that  are  "generally  conceded"  are  sometimes  wrong, 
and  this  is  an  instance.  A  blue  flame  indicates  combustion  of  a 
thorough  mixture  of  air  and  gas.  The  air  supply  may  be  just  suf- 
ficient to  make  complete  combustion,  in  which  case  the  temperature 
at  the  point  of  the  flame  will  be  considerably  over  3000°  F.,  or  it 
may  be  greatly  in  excess,  in  which  case  the  temperature  will  be  lower. 
A  white  flame  indicates  delayed  combustion,  the  white  color  being 
due  to  particles  of  incandescent  carbon,  but  these  particles,  when 
they  reach  the  margin  of  the  flame  and  there  come  in  contact  with 
heated  air  are  burned  to  invisible  carbon  dioxide.  Whether  the  flame 
is  blue  or  white,  whether  combustion  is  instantaneous  or  delayed,  the 
same  quantity  of  fuel  burned  will  generate  the  same  quantity  of  heat, 
and  if  the  air  supply  is  the  same  in  both  cases  the  boiler  efficiency 
should  be  the  same.  But  the  efficiency  will  be  decreased  with  either 
the  blue  or  the  white  flame  if  the  air  supply  is  excessive,  and  in  case 
of  the  white  flame  if  it  is  allowed  to  touch  the  surface  of  the  boiler 
before  the  combustion  is  complete,  so  that  the  white-hot  carbon  parti- 
cles are  cooled  and  become  particles  of  soot  instead  of  being  burned. 


CHAPTER  XVIII.* 


PROPERTIES  OF  WATER  AND  OF  STEAM— FACTORS  OF  EVAPORA 

TION— CHIMNEYS. 

WATER 

Weight  of  Water  at  Different  Temperatures, — The  weight  of 
water  at  maximum  density,  39.1°,  is  generally  taken  at  the  figure 
given  by  Rankine,  62.425  Ibs.  per  cu.  ft.  Some  authorities  give  as  low 
as  62.379.  The  figure  62.5  commonly  given  is  approximate.  The 
highest  authoritative  figure  is  62.425.  At  62°  F.  the  figures  range 
from  62.291  to  62.360.  The  figure  62.355  is  generally  accepted  as  the 
most  accurate. 

At  32°  F.  figures  given  by  different  writers  range  from  62.379  to 
62.418.  Clark  gives  the  latter  figure  and  Hamilton  Smith,  Jr.  (from 
Roseiti),  gives  62.416. 

Weight  of  Water  at  Temperatures  above  200°  F.  (Landolt  and 
Bernstein's  Tables,  1905.) 


Pounds 

Pounds 

Pounds 

Pounds 

Pounds 

Lbs. 

DFe, 

per 
Cubic 

D^, 

Cubic 

DF8' 

Cubic 

Deg. 
F. 

per 
Cubic 

Deg. 
F. 

Cubic 

Deg. 
F. 

Per 

Cubic 

Foot. 

Foot. 

Foot. 

Foot. 

Foot. 

Foot. 

200 

60.12 

270 

58.26 

340 

55.94 

410 

53.0 

480 

49.7 

550 

45.6 

210 

59.88 

280 

57.96 

350 

55.57 

420 

52.6 

490 

49.2 

560 

44.9 

220 

59.63 

290 

57  .  65 

360 

55.18 

430 

52.2 

500 

48.7 

570 

44.1 

230 

59.37 

300 

57.33 

370 

54.78 

440 

51.7 

510 

48.1 

580 

43.3 

240 

59.11 

310 

57.00 

380 

54.36 

450 

51.2 

520 

47.6 

590 

42.6 

250 

58.83 

320 

56.66 

390 

53.94 

460 

50.7 

530 

47.0 

600 

41.8 

260 

58.55 

330 

56.30 

400 

53.5 

470 

52.2 

540 

46.3 

Weight  of  Water  per  Cubic  Foot,  from  32°  to  212°  F.,  and  heat- 
units  per  pound,  reckoned  above  32°  F. :  The  figures  for  weight  of 
water  in  the  following  table,  mad.e  by  interpolating  the  table  given 
by  Clark  as  calculated  from  Rankine's  formula,  with  corrections  for 
apparent  errors,  was  published  by  the  author  in  1884,  Trans.  A. 

*  This  chapter  is  chiefly  compiled  from  the  author's  "  Mechanical  Engineers' 
Pocketbook." 

658 


PROPERTIES  OF  WATER. 


659 


S.  M.  E.,  vi.  90.  The  figures  for  heat-units  are  from  Marks  and 
Davis's  Steam  Tables,  1909.  (For  heat-units  above  212°  see  Steam 
Tables.) 


Temperature,  1 
Deg.  F. 

.2.2 

—  '& 

Ifel 

•53  a^ 

£ 

Heat-units. 

Temperature, 
Deg.  F. 

|| 
I|l 

5  G,fz< 
£ 

.1 
'8 

3 
eS 

HI 

w 

Temperature, 
Deg.  F. 

l| 

i?1 

•?&£ 
£ 

Heat-units. 

Temperature, 
Deg.  F. 

JJ 

£$i 

•§•&£ 
& 

Heat-units. 

32 

62.42 

0 

78 

62.25 

46.04 

123 

61.68 

90.90 

168 

60.81 

135.86 

33 

62.42 

1.01 

79 

62.24 

47.04 

124 

61.67 

91.90 

169 

60.79 

136.86 

34 

62.42 

2.02 

80 

62.23 

48.03 

125 

61.65 

92.90 

170 

60.77 

137.87 

35 

62.42 

3.02 

81 

62.22 

49.03 

126 

61.63 

93.90 

171 

60.75 

138.87 

36 

62.42 

4.03 

82 

62.21 

50.03 

127 

61.61 

94.89 

172 

60.73 

139.87 

37 

62.42 

5.04 

83 

62.20 

51.02 

128 

61.60 

95.89 

173 

60.70 

140.87 

38 

62.42 

6.04 

84 

62.19 

52.02 

129 

61.58 

96.89 

174 

60.68 

141.87 

39 

62.42 

7.05 

85 

62.18 

53.02 

130 

61.56 

97.89 

175 

60.66 

142.87 

40 

62.42 

8.05 

86 

62.17 

54.01 

131 

61.54 

98.89 

176 

60.64 

143.87 

41 

62.42 

9.05 

87 

62.16 

55.01 

132 

61.52 

99.88 

177 

60.62 

144.88 

42 

62.42 

10.06 

88 

62.15 

56.01 

133 

61.51 

100.88 

178 

60.59 

145.88 

43 

62.42 

11.06 

89 

62.14 

57.00 

134 

61.49 

101.88 

179 

60.57 

146.88 

44 

62.42 

12.06 

90 

62.13 

58.00 

135 

61.47 

102.88 

180 

60.55 

147.88 

45  62.42 

13.07 

91 

62.12 

59.00 

136 

61.45 

103.88 

181 

60.53 

148.88 

46  62.42 

14.07 

92 

62.11 

60.00 

137 

61.43 

104.87 

182 

60.50 

149.89 

47162.42 

15.07 

93 

62.10 

60.99 

138 

61.41 

105.87 

183 

60.48 

150.89 

48 

62.41 

16.07 

94 

62.09 

61.99 

139 

61.39 

106.87 

184 

60.46 

151.89 

49 

62.41 

17.08 

95 

62.08 

62.99 

140 

61.37 

107.87 

185 

60.44 

152.89 

50 

62.41 

18.08 

£6 

62.07 

63.98 

141 

61.36 

108.87 

186 

60.41 

153.89 

51 

62.41 

19.08 

97 

62.06 

64.98 

142 

61.34 

109.87 

187 

60.39 

154.90 

52 

62.40 

20.08 

98 

62.05 

65.98 

143 

61.32 

110.87 

188 

60.37 

155.90 

53 

62.40 

21.08 

99 

62.03 

66.97 

144 

61.30 

111.87 

189 

60.34 

156.90 

54 

62.40 

22.08 

100 

62.02 

67.97 

145 

61.28 

112.86 

190 

60.32 

157.91 

55 

62.39 

23.08 

101 

62.01 

68.97 

146 

61.26 

113.86 

191 

60.29 

158.91 

56 

62.39 

24.08 

102 

62.00 

69.96 

147 

61.24 

114.86 

192 

60.27 

159.91 

57 

62.39 

25.08 

103 

61.99 

70.96 

148 

61.22 

115.86 

193 

60.25 

160.91 

58 

62.38 

26.08 

104 

61.97 

71.96 

149 

61.20 

116.86 

194 

60.22 

161.92 

59 

62.38 

27.08 

105 

61.96 

72.95 

150 

61.18 

117.86 

195 

60.20 

162.92 

60 

62.37 

28.08 

106 

61.95 

73.95 

151 

61.16 

118.86 

196 

60.17 

163.92 

61 

62.37 

29.08 

107 

61.93 

74.95 

152 

61.14 

119.86 

197 

60.15 

164.93 

62 

62.36 

30.08 

108 

61.92 

75.95 

153 

61.12 

120.86 

198 

60.12 

165.93 

63 

62.36 

31.07 

109 

61.91 

76.94 

154 

61.10 

121.86 

199 

60.10 

166.94 

64 

62.35 

32.07 

110 

61.89 

77.94 

155 

61.08 

122.86 

200 

60.07 

167.94 

65 

62.34 

33.07 

111 

61.88 

78.94 

156 

61.06 

123.86 

201 

60.05 

168.94 

66 

62.34 

34.07 

112 

61.86 

79.93 

157 

61.04 

124.86 

202 

60.02 

169.95 

67 

62.33 

35.07 

113 

61.85 

80.93 

158 

61.02 

125.86 

203 

60.00 

170.95 

68 

62.33 

36.07 

114 

61.83 

81.93 

159 

61.00 

126.86 

204 

59.97 

171.96 

69 

62.32 

37.06 

115 

61.82 

82.92 

160 

60.98 

127.86 

205 

59.95 

172.96 

70 

62.31 

38.06 

116 

61.80 

83.92 

1-61 

60.96 

128.86 

206 

59.92 

173.97 

71 

62.31 

39.06 

117 

61.78 

84.92 

162 

60.94 

129.86 

207 

59.89 

174.97 

72 

62.30 

40.05 

118 

61.77 

85.92 

163 

60.92 

130.86 

208 

59.87 

175.98 

73 

62.29 

41.05 

119 

61.75 

86.91 

164 

60.90 

131.86 

209 

59.84 

176.98 

74 

62.28 

42.05 

120 

61.74 

87.91 

165 

60.87 

132.86 

210 

59.82 

177.99 

75 

62.28 

43.05 

121 

61.72 

88.91 

166 

60.85 

133.86 

211 

59.79 

178.99 

76 

62.27 

43.04 

122 

61.70 

89.91 

167 

60.83 

134.86 

212 

59.76' 

180.00 

77 

62.26 

45.04 

660  STEAM-BOILER  ECONOMY. 

Later  authorities  give  figures  for  the  weight  of  water  which  differ 
in  the  second  decimal  place  only  from  those  given  above,  as  follows : 

Temp.  F 40  50  60  70  80  90 

Lbs.percu.ft.    62.43  62.42  62.37  62.30  62.22  62.11 

Temp.  F 100  110  120  130  140  150 

Lbs.percu.ft.   62.00  61.86  61.71  61.55  61.38  61.18 

Temp.  F 160  170  180  190  200  210 

Lbs.percu.ft.   61.00  60.80  60.50  60.36  60.12  59.88 

STEAM. 

The  Temperature  of  Steam  in  contact  with  water  depends  upon 
the  pressure  under  which  it  is  generated.  At  the  ordinary  atmos- 
pheric pressure  (14.7  Ibs.  per  sq.  in.)  its  temperature  is  212°  F.  As 
the  pressure  is  increased,  as  by  the  steam  being  generated  in  a  closed 
vessel,  its  temperature,  and  that  of  the  water  in  its  presence,  increases. 

Saturated  Steam  is  steam  of  the  temperature  due  to  its  pressure 
— not  superheated. 

Superheated  Steam  is  steam  heated  to  a  temperature  above  that 
due  to  its  pressure. 

Dry  Steam  is  steam  which  contains  no  moisture.  It  may  be  either 
saturated  or  superheated. 

Wet  Steam  is  steam  containing  intermingled  moisture,  mist,  or 
spray.  It  has  the  same  temperature  as  dry  saturated  steam  of  the 
same  pressure. 

Water  introduced  into  the  presence  of  superheated  steam  will  flash 
into  vapor  until  the  temperature  of  the  steam  is  reduced  to  that  due  to 
its  pressure.  Water  in  the  presence  of  saturated  steam  has  the  same 
temperature  as  the  steam.  Should  cold  water  be  introduced,  lowering 
the  temperature  of  the  whole  mass,  some  of  the  steam  will  be  con- 
densed, reducing  the  pressure  and  temperature  of  the  remainder,  until 
an  equilibrium  is  established. 

The  total  heat  in  steam  (above  32°)  includes  three  elements: 

1st.  The  heat  required  to  raise  the  temperature  of  the  water  to 
the  temperature  of  the  steam. 

2d.  The  heat  required  to  evaporate  the  water  at  that  temperature, 
called  internal  latent  heat. 

3d.  The  latent  heat  of  volume,  or  the  external  work  done  by  the 
steam  in  making  room  for  itself  against  the  pressure  of  the  super- 
incumbent atmosphere  (or  surrounding  steam  if  inclosed  in  a  vessel). 

The*  sum  of  the  last  two  elements  is  called  the  latent  heat  of 
steam. 


PROPERTIES  OF  STEAM.  661 

Heat  Required  to  Generate  1  Pound  of  Steam  at  212°. — 

Heat-units, 

Sensible  heat,  to  raise  1  Ib.  water  from  32°  to  212°=  180.0 

Latent  heat,  1,  of  the  formation  of  span  at  212°..  .  =     897.6 
2,  of  expansion  against  the  atmospheric 
pressure,  2116.4  Ibs.  per  sq.  ft.  X 
26.79  cu.ft.  =  55,786  foot-pounds 
-5-778..  ..=       72.8       970.4 


Total  heat  above  32° 1150.4 

Identification  of  Dry  Steam  by  Appearance  of  a  Jet. — Prof. 
Denton  (Trans.  A.  S.  M.  E.,  vol.  x)  found  that  jets  of  steam  show 
unmistakable  change  of  appearance  to  the  eye  when  steam  varies  less 
than  1  per  cent  from  the  condition  of  saturation  either  in  the  direc- 
tion of  wetness  or  superheating. 

If  a  jet  of  steam  flow  from  a  boiler  into  the  atmosphere  under 
circumstances  such  that  very  little  loss  of  heat  occurs  through  radia- 
tion, etc.,  and  the  jet  be  transparent  close  to  the  orifice,  or  be  even  a 
grayish-white  color,  the  steam  may  be  assumed  to  be  so  nearly  dry 
that  no  portable  condensing  calorimeter  will  be  capable  of  measuring 
the  amount  of  water  in  the  steam.  If  the  jet  be  strongly  white,  the 
amount  of  water  may  be  roughly  judged  up  to  about  2  per  cent,  but 
beyond  this  a  calorimeter  only  can  determine  the  exact  amount  of 
moisture. 


662 


STEAM-BOILER  ECONOMY. 


PROPERTIES   OF  SATURATED   STEAM. 

(Condensed  from  Marks  and  Davis's  Steam  Tables  and  Diagrams,  1909,  by  permission  of  the 
publishers,  Longmans,  Green  &  Co.) 


Vac- 
uum, 
Inches 
of 
Mer- 
cury. 

Absolute 
Pressures, 
Lbs.  per 
Sq.   In. 

Tempera- 
ture, 
Fahren- 
heit. 

Total  Heat  Above 
32°  F. 

Latent 
Heat  L, 
=  H  -h. 
Heat- 
Units. 

Volume, 
Cu.  Ft. 
in  1  Lb. 
of  Steam. 

Weight  of 
1  Cu.  Ft. 
Steam,  Lb. 

In  the 
Water 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

29.74 

0.0886 

32 

0.00 

1073.4 

1073.4 

3294 

0.000304 

29.67 

0.1217 

40 

8.05 

1076.9 

1068.9 

2438 

0.000410 

29.56 

0.1780 

50 

18.08 

1081.4 

1063.3 

1702 

0.000587 

29.40 

0.2562 

60 

28.08 

1085.9 

1057.8 

1208 

0.000828 

29.18 

0.3626 

70 

38.06 

1090.3 

1052.3 

871 

0.001148 

28.89 

0.505 

80 

48.03 

1094.8 

1046.7 

636.8 

0.001570 

28.50 

0.698 

90 

58.00 

1099.2 

1041.2 

469.3 

0.002131 

28.00 

0.946 

100 

67.97 

1103.6 

1035.6 

350.8 

0.002851 

27.88 

1 

101.83 

69.8 

1104.4 

1034.6 

333.0 

0.00300 

25.85 

2 

126.15 

94.0 

1115.0 

1021.0 

173.5 

0.00576 

23.81 

3 

141.52 

109.4 

1121.6 

1012.3 

118.5 

0.00845 

21.78 

4 

153.01 

120.9 

1126.5 

1005.7 

90.5 

0.01107 

19.74 

5 

162.28 

130.1 

1130.5 

1000.3 

73.33 

0.01364 

17.70 

6 

170.06 

137.9 

1133.7 

995.8 

61.89 

0.01616 

15.67 

7 

176.85 

144.7 

1136.5 

991.8 

53.56 

0.01867 

13.63 

8 

182.86 

150.8 

1139.0 

988.2 

47.27 

0.02115 

11.60 

9 

188.27 

156.2 

1141.1 

985.0 

42.36 

0.02361 

9.56 

10 

193.22 

161.1 

1143.1 

982.0 

38.38 

0.02606 

7.52 

11 

197.75 

165.7 

1144.9 

979.2 

35.10 

0.02849 

5.49 

12 

201  .  96 

169.9 

1146.5 

976.6 

32.36 

0.03090 

3.45 

13 

205.87 

173.8 

1148.0 

974.2 

30.03 

0.03330 

1.42 

14 

209.55- 

177.5 

1149.4 

971.9 

28.02 

0.03569 

Ibs. 

gauge 

14.70 

212 

180.0 

1150.4 

970.4 

26.79 

0.03732 

0.3 

15 

213.0 

181.0 

1150.7 

969.7 

26.27 

0.03806 

1.3 

16 

216.3 

184.4 

1152.0 

967.6 

24.79 

0.04042 

2.3 

17 

219.4 

187.5 

1153.1 

965.6 

23.38 

0.04277 

3.3 

18 

222.4 

190.5 

1154.2 

963.7 

22.16 

0.04512 

4.3 

19 

225.2 

193.4 

1155.2 

961.8 

21.07 

0.04746 

5.3 

20 

228.0 

196.1 

1156.2 

960.0 

20.08 

0.04980 

6.3 

21 

230.6 

198.8 

1157.1 

958.3 

19.18 

0.05213 

7.3 

22 

233.1 

201.3 

1158.0 

956.7 

18.37 

0.05445 

8.3 

23 

235.5 

203.8 

1158.8 

955.1 

17.62 

0'.  05676 

9.3 

24 

237.8 

206.1 

1159.6 

953.5 

16.93 

0.05907 

10.3 

25 

240.1 

208.4 

1160.4 

952.0 

16.30 

0.0614 

11.3 

26 

242.2 

210.6 

1161.2 

950.6 

15.72 

0.0636 

12.3 

27 

244  .4 

212.7 

1161.9 

949.2 

15.18 

0.0659 

13.3 

28 

246.4 

214.8 

1162.6 

947.8 

14.67 

0.0682 

14.3 

29 

248.4 

216.8 

1163.2 

946.4 

14.19 

0.0705 

15.3 

30 

250.3 

218.8 

1163.9 

945.1 

13.74 

0.0728 

16.3 

31 

252.2 

220.7 

1164.5 

943.8 

13.32 

0.0751 

17.3 

32 

254.1 

222.6 

1165.1 

942.5 

12.93 

0.0773 

18.3 

33 

255.8 

224.4 

1165.7 

941.3 

12.57 

0.0795 

19.3 

34 

257.6 

226.2 

1166.3 

940.1 

12.22 

0.0818 

20.3 

35 

259.3 

227.9 

1166.8 

938.9 

11.89 

0.0841 

21.3 

36 

261.0 

229.6 

1167.3 

937.7 

11.58 

0.0863 

PROPERTIES  OF  STEAM 


663 


PROPERTIES  OF  SATURATED  STEAM. — Continued. 


Gauge 
Pres- 
sure 
Lbs. 
per 
Sq.  In. 

Absolute 
Pressure 
Lbs.  per 
Sq.  In. 

Tempera- 
ture, 
Fahren- 
heit. 

Total  Heat  Above 
32°  F. 

Latent 
Heat,  L 
=  H  -h. 
Heat- 
units. 

Volume, 
Cu.  Ft. 
in  1  Lb. 
of  Steam. 

Weight  of 
1  Cubic  Ft. 
Steam,  Lb. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

22.3 

37 

262.6 

231.3 

1167.8 

936.6 

11.29 

0.0886 

23.3 

38 

264.2 

232.9 

1168.4 

935.5 

11.01 

0.0908 

24.3 

39 

265.8 

234.5 

1168.9 

934.4 

10.74 

0.0931 

25.3 

40 

267.3 

236.1 

1169.4 

933.3 

10.49 

0.0953 

26.3 

41 

268.7 

237.6 

1169.8 

932.2 

10.25 

0.0976 

27.3 

42 

270.2 

239.1 

1170.3 

931.2 

10.02 

0.0998 

28.3 

43 

271.7 

240.5 

1170.7 

930.2 

9.80 

0.1020 

29.3 

44 

273.1 

242.0 

1171.2 

929.2 

9.59 

0.1043 

30.3 

45 

274.5 

243.4 

1171.6 

928.2 

9.39 

0.1065 

31.3 

46 

275.8 

244.8 

1172.0 

927.2 

9.20 

0.1087 

32.3 

47 

277.2 

246.1 

1172.4 

926.3 

9.02 

0.1109 

33.3 

48 

278.5 

247.5 

1172.8 

925.3 

8.84 

0.1131 

34.3 

49 

279.8 

248.8 

1173.2 

924.4 

8.67 

0.1153 

35.3 

50 

281.0 

250.1 

1173.6 

•923.5 

8.51 

0.1175 

36.3 

51 

282.3 

251.4 

1174.0 

922.6 

8.35 

0.1197 

37.3 

52 

283.5 

252.6 

1174.3 

921.7 

8.20 

0.1219 

38.3 

53 

284.7 

253.9 

1174.7 

920.8 

8.05 

0.1241  ' 

39.3 

54 

285.9 

255.1 

1175.0 

919.9 

7.91 

0.1263 

40.3 

55 

287.1 

256.3 

1175.4 

919.0 

7.78 

0.1285 

41.3 

56 

288.2 

257.5 

1175.7 

918.2 

7.65 

0.1307 

42.3 

57 

289.4 

258.7 

1176.0 

917.4 

7.52 

0.1329 

43.3 

58 

290.5 

259.8 

1176.4 

916.5 

7.40 

0.1350 

44.3 

59 

291.6 

261.0 

1176.7 

915.7 

7.28 

0.1372 

45.3 

60 

292.7 

262.1 

1177.0 

914.9 

7.17 

0.1394 

46.3 

61 

293.8 

263.2 

1177.3 

914.1 

7.06 

0.1416 

47.3 

62 

294.9 

264.3 

1177.6 

913.3 

6.95 

0.1438 

48.3 

63 

295.9 

265.4 

1177.9 

912.5 

6.85 

0.1460 

49.3 

64 

297.0 

266.4 

1178.2 

911.8 

6.75 

0  .  1482 

50.3 

65 

298.0 

267.5 

1178.5 

911.0 

6.65 

0.1503 

51.3 

66 

299.0 

268.5 

1178.8 

910.2 

6.56 

0.1525 

52.3 

67 

300.0 

269.6 

1179.0 

909.5 

6.47 

0.1547 

53.3 

68 

301.0 

270.6 

1179.3 

908.7 

6.38 

0.1569 

54.3 

69 

302.0 

271.6 

1179.6 

908.0 

6.29 

0.1590 

55.3 

70 

302.9 

272.6 

1179.8 

907.2 

6.20 

0.1612 

56.3 

71 

303.9 

273.6 

1180.1 

906.5 

6.12 

0.1634 

57.3 

72 

304.8 

274.5 

1180.4 

905.8 

6.04 

0.1656 

58.3 

73 

305.8 

275.5 

1180.6 

905.1 

5.96 

0.1678 

59.3 

74 

306.7 

276.5 

1180.9 

904.4 

5.89 

0.1699 

60.3 

75 

307.6 

277.4 

1181.1 

903.7 

5.81 

0.1721 

61.3 

76 

308.5 

278.3 

1181.4 

903.0 

5.74 

0.1743 

62.3 

77 

309.4 

279.3 

1181.6 

902.3 

5.67 

0.1764 

63.3 

78 

310.3 

280.2 

1181.8 

901.7 

5.60 

0.1786 

64.3 

79 

311.2 

281.1 

1182.1 

901.0 

5.54 

0.1808 

65.3 

80 

312.0 

282.0 

1182.3 

900.3 

5.47 

0.1829 

66.3 

81 

312.9 

282.9 

1182.5 

899.7 

5.41 

0.1851 

67.3 

82 

313.8 

283.8 

1182.8 

899.0 

5.34 

0.1873 

68.3 

83 

314.6 

284.6 

1183.0 

898.4 

5.28 

0.1894 

69.3 

84 

315.4 

285.5 

1183.2 

897.7 

5.22 

0.1915 

70.3 

85 

316.3 

286.3 

1183.4 

897.1 

5.16 

0.1937 

664 


STEAM-BOILER  ECONOMY. 


PROPERTIES  OF  SATURATED  STEAM — Continued. 


Gauge 
Pres- 
sure, 
Lbs. 
per 
Sq.  In. 

Absolute 
Pressure, 
Lbs.  per 
Sq.    In. 

Tempera- 
ture, 
Fahren- 
heit. 

Total  Heat  Above 
32°  F. 

Latent 
Heat,  L 
-H  -h 
Heat- 
units. 

Volume, 
Cu.  Ft. 
in  1  Lb. 
of  Steam. 

Weight  of 
1  Cubic  Ft. 
Steam,  Lb. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
H 
Heat- 
units. 

71.3 

86 

317.1 

287.2 

1183.6 

896.4 

5.10 

0.1959 

72.3 

87 

317.9 

288.0 

1183.8 

895.8 

5.05 

0.1980 

73.3 

88 

318.7 

288.9 

1184.0 

895.2 

5.00 

0.2001 

74.3 

89 

319.5 

289.7 

1184.2 

894.6 

4.94 

0.2023 

75.3 

90 

320.3 

290.5 

1184.4 

893  .  9 

4.89 

0.2044 

76.3 

91 

321.1 

291.3 

1184.6 

893.3 

4.84 

0.2065 

77.3 

92 

321.8 

292.1 

1184.8 

892.7 

4.79 

0.2087 

78.3 

93 

322.6 

292.9 

1185.0 

892.1 

4.74 

0.2109 

79.3 

94 

323.4 

293.7 

1185.2 

891.5 

4.69 

0.2130 

80.3 

95 

324.1 

294.5 

1185.4 

890.9 

4.65 

0.2151 

81.3 

96 

324.9 

295.3 

1185.6 

890.3 

4.60 

0.2172 

82.3 

97 

325.6 

296.1 

1185.8 

889.7 

4.56 

0.2193 

83.3 

98 

326.4 

296.8 

1186.0 

889.2 

4.51 

0.2215 

84.3 

99 

327.1 

297.6 

1186.2 

888.6 

4.47 

0.2237 

85.3 

100 

327.8 

298.3 

1186.3 

888.0 

4.429 

0.2258 

87.3 

102 

329.3 

299.8 

1186.7 

886.9 

4.347 

0.2300 

89.3 

104 

330.7 

301.3 

1187.0 

885.8 

4.268 

0.2343 

91.3 

106 

332.0 

302.7 

1187.4 

884.7 

4.192 

0.23F6 

93.3 

108 

333.4 

304.1 

1187.7 

883.6 

4.118 

0.2429 

95.3 

110 

334.8 

305.5 

1188.0 

882.5 

4.047 

0.2472 

97.3 

112 

336.1 

306.9 

1188.4 

881.4 

3.978 

0.2514 

99.3 

114 

337.4 

308.3 

1188.7 

880.4 

3  .  912 

0.2556 

101.3 

116 

338.7 

309.6 

1189.0 

879.3 

3.848 

0.2599 

103.3 

118 

340.0 

311.0 

1189.3 

878.3 

3.786 

0.2641 

105.3 

120 

341.3 

312.3 

1189.6 

877.2 

3.726 

0.2683 

107.3 

122 

342.5 

313.6 

1189.8 

876.2 

3.668 

0.2726 

109.3 

124 

343.8 

314.9 

1190.1 

875.2 

3.611 

0.2769 

111.3 

126 

345  '.0 

316.2 

1190.4 

874.2 

3.556 

0.2812 

113.3 

128 

346.2 

317.4 

1190.7 

873.3 

3.504 

0.2854 

115.3 

130 

347.4 

318.6 

1191.0 

872.3 

3.452 

0.2897 

117.3 

132 

348.5 

319.9 

1191.2 

871  .3 

3.402 

0.2939 

119.3 

134 

349.7 

321.1 

1191.5 

870.4 

3.354 

0.2981 

121.3 

136 

350.8 

322.3 

1191.7 

869.4 

3.308 

0.3023 

123.3 

138 

352.0 

323.4 

1192.0 

868.5 

3.263 

0.3065 

125.3 

140 

353.1 

324.6 

1192.2 

867.6 

3.219 

0.3107 

127.3 

142 

354.2 

325.8 

1192.5 

866.7 

3.175 

0.3150 

129.3 

144 

355.3 

326.9 

1192.7 

865.8 

3.133 

0.3192 

131.3 

146 

356.3 

328.0 

1192.9 

864.9 

3.092 

0.3234 

133.3 

148 

357.4 

329.1 

1193.2 

864.0 

3.052 

0.3276 

135.5 

150 

358.5 

330.2 

1193.4 

863.2 

3.012 

0.3320 

137.3 

152 

359.5 

331.4 

1193.6 

862.3 

2.974 

0  .  3362 

139.3 

154 

360.5 

332.4 

1193.8 

861.4 

2.938 

0.3404 

141.3 

156 

361.6 

333.5 

1194.1 

860.6 

2.902 

0  .  3446 

143.3 

158 

362.6 

334.6 

1194.3 

859.7 

2.868 

0.3488 

145.3 

160 

363.6 

335.6 

1194.5 

858.8 

2.834 

0.3529 

147.3 

162 

364.6 

336.7 

1194.7 

858.0 

2.801 

0.3570 

149.3 

164 

365.6 

337.7 

1194.9 

857.2 

2.769 

0.3612 

151.3 

166 

366.5 

338.7 

1195.1 

856.4 

2.737 

0.3654 

153.3 

168 

367.5 

339.7 

1195.3 

855.5 

2.706 

0.3696 

PROPERTIES  OF  STEAM. 

PROPERTIES   OF  SATURATED   STEAM. — Continued. 


665 


Gage 

Total  H 
32 

eat  Above 
°F. 

Latent 

Pres- 
sure, 
Lbs. 
per 
Sq.  In. 

Absolute 
Pressure, 
Lbs.  per 
Sq.  In. 

Tempera- 
ture, 
Fahren- 
heit. 

In  the 
Water. 
h 
Heat- 
units. 

In  the 
Steam. 
// 
Heat- 
units. 

Heat,  L 
=  H  -h. 
Heat- 
units. 

Volume, 
Cu.  Ft. 
in  1  Lb. 
of  Steam. 

Weight  of 
1  Cubic  Ft. 
Steam,  Lb. 

155.3 

170 

368.5 

340.7 

1195.4 

854.7 

2.675 

0.3738 

157.3 

172 

369.4 

341.7 

1195.6 

853.9 

2.645 

0.3780 

159.3 

174 

370.4 

342.7 

1195.8 

853.1 

2.616 

0.3822 

161.3 

176 

371.3 

343.7 

1196.0 

852.3 

2.588 

0.3864 

163.3 

178 

372.2 

344.7 

1196.2 

851.5 

2.560 

0.3906 

165.3 

180 

373.1 

345.6 

1196.4 

850.8 

2.533 

0.3948 

167.3 

182 

374.0 

346.6 

1196.6 

850.0 

2.507 

0.3989 

169.3 

184 

374.9 

347.6 

1196.8 

849.2 

2.481 

0.4031 

171.3 

186 

375.8 

348.5 

1196.9 

848.4 

2.455 

0.4073 

173.3 

188 

376.7 

349.4 

1197.1 

847.7 

2.430 

0.4115 

175.3 

190 

377.6 

350.4 

1197.3 

846.9 

2.406 

0.4157 

177.3 

192 

378.5 

351.3 

1197.4 

846.1 

2.381 

0.4199 

179.3 

194 

379.3 

352.2 

1197.6 

845.4 

2.358 

0.4241 

181.3 

196 

380.2 

353.1 

1197.8 

844.7 

2.335 

0.4283 

183.3 

198 

381.0 

354.0 

1197.9 

843.9 

2.312 

0.4325 

185.3 

200 

381.9 

354.9 

1198.1 

843.2 

2.290 

0.437 

190.3 

205 

384.0 

357.1 

1198.5 

841.4 

2.237 

0.447  . 

195.3 

210 

386.0 

359.2 

1198.8 

839.6 

2.187 

0.457 

200.3 

215 

388.0 

361.4 

1199.2 

837.9 

2.138 

0.468 

205.3 

220 

389.9 

363.4 

1199.6 

836.2 

2.091 

0.478 

210.3 

225 

391.9 

365.5 

1199.9 

834.4 

2.046 

0.489 

215.3 

230 

393.8 

367.5 

1200.2 

832.8 

2.004 

0.499 

220.3 

235 

395.6 

369.4 

1200.6 

831.1 

1.964 

0.509 

225.3 

240 

397.4 

371.4 

1200.9 

829.5 

.924 

0.520 

230.3 

245 

399.3 

373.3 

1201.2 

827.9 

.887 

0.530 

235.3 

250 

401.1 

375.2 

1201.5 

826.3 

.850 

0.541 

245.3 

260 

404.5 

378.9 

1202.1 

823.1 

.782 

0.561 

255.3 

270 

407.9 

382.5 

1202.6 

820.1 

.718 

0.582 

265.3 

280 

411.2 

386.0 

1203.1 

817.1 

.658 

0.603 

275.3 

290 

414.4 

389.4 

1203.6 

814.2 

.602 

0.624 

285.3 

300 

417.5 

392.7 

1204.1 

811.3 

.551 

0.645 

295.3 

310 

420.5 

395.9 

1204.5 

808.5 

.502 

0.666 

305.3 

320 

423.4 

399.1 

1204.9 

805.8 

.456 

0.687 

315.3 

330 

426.3 

402.2 

1205.3 

803.1 

.413 

0.708 

325.3 

340 

429.1 

405.3 

1205.7 

800.4 

.372 

0.729 

335.3 

350 

431.9 

408.2 

1206.1 

797.8 

.334 

0.750 

345.3 

360 

434.6 

411.2 

1206.4 

795.3 

1.298 

0.770 

355.3 

370 

437.2 

414.0 

1206.8 

792.8 

1.264 

0.791 

365.3 

380 

439.9 

416.8 

1207.1 

790.3 

1.231 

0.812 

375.3 

390 

442.3 

419.5 

1207.4 

787.9 

1.200 

0.833 

385.3 

400 

444.8 

422 

1208 

786 

1.17 

0.86 

435.3 

450 

456.5 

435 

1209 

774 

1.04 

0.96 

485.3 

500 

467.3 

448 

1210 

762 

0.93 

1.08 

535.3 

550 

477.3 

459 

1210 

751 

0.83 

1.20 

585.3 

600 

486.6 

469 

1210 

741 

0.76 

1.32 

666 


STEAM-BOILER  ECONOMY. 


PROPERTIES  OF  SUPERHEATED  STEAM. 

(Condensed  from  Marks  and  Davis's  Steam  Tables  and  Diagrams.) 
v  =specific  volume  in  cu.ft.  per  lb.,  h  =total  heat,  from  water  at  32°  F.  in  B.T.U.  per  Ib. 


Press. 
Abs. 
Lbs.  per 
Sq.  In. 

Temp. 

Sat. 
Steam. 

Degrees  of  Superheat. 

0 

20 

50 

100 

150 

200 

250 

300 

400 

500 

20 

228.0 

v  20.08 

20.73 

21.69 

23.25 

24.80 

26.33 

27.85 

29.37 

32.39 

35.40 

h  1156.2 

1165.7 

1179.9 

1203.5 

1227.1 

1250.6 

1274.1 

1297.6 

1344.8 

1392.2 

40 

267.3 

v  10.49 

10.83 

11.33 

12.13 

12.93 

13.70 

14.48 

15.25 

16.78 

18.30 

h  1169.4 

1179.3 

1194.0 

1218.4 

1242.4 

1266.4 

1290.3 

1314.1 

1361.6 

1409.3 

60 

292.7 

v  7  .  17 

7.40 

7.75 

8.30 

8.84 

9.36 

9.89 

10.41 

11.43 

12.45 

h  1177.0 

1187.3 

1202.6 

1227.6 

1252.1 

1276.4 

1300.4 

1324.3 

1372.2 

1420.0 

80 

312.0 

v  5.47 

5.65 

5.92 

6.34 

6.75 

7.17 

7.56 

7.95 

8.72 

9.49 

h  1182.3 

1193.0 

1208.8 

1234.3 

1259.0 

1283  .  6 

1307.8 

1331.9 

1379.8 

1427.9 

100 

327.8 

v  4.43 

4.58 

4.79 

5.14 

5.47 

5.80 

6.12 

6.44 

7.07 

7.69 

h  1186.3 

1197.5 

1213.8 

1239.7 

1264.7 

1289.4 

1313.6 

1337.8 

1385.9 

1434.1 

120 

341.3 

v  3.73 

3.85 

4.04 

4.33 

4.62 

4.89 

5.17 

5.44 

5.96 

6.48 

h  1189.6 

1201.1 

1217.9 

1244.1 

1269.3 

1294.1 

1318.4 

1342.7 

1391.0 

1439.4 

140 

353.1 

v  3.22 

3.32 

3.49 

3.75 

4.00 

4.24 

4.48 

4.71 

5.16 

5.61 

h  1192.2 

1204.3 

1221.4 

1248.0 

1273.3 

1298.2 

1322.6 

1346.9 

1395.4 

1443.8 

160 

363.6 

v  2.83 

2.93 

3.07 

3.30 

3.53 

3.74 

3.95 

4.15 

4.56 

4.95 

h  1194.5 

1207.0 

1224.5 

1251.3 

1276.8 

1301.7 

1326.2 

1350.6 

1399.3 

1447.9 

180 

373.1 

v  2.53 

2.62 

2.75 

2.96 

3.16 

3.35 

3.54 

3.72 

4.09 

4.44 

h  1196.4 

1209.4 

1227.2 

1254.3 

1279.9 

1304.8 

1329.5 

1353.9 

1402.7 

1451.4 

200 

381.9 

v  2.29 

2.37 

2.49 

2.68 

2.86 

3.04 

3.21 

3  .  38 

3.71 

4.03 

h  1198.1 

1211.6 

1229.8 

1257.1 

1282.6 

1307.7 

1332.4 

1357.0 

1405.9 

1454.7 

220 

389.9 

v  2.09 

2.16 

2.28 

2.45 

2.62 

2.78 

2.94 

3.10 

3.40 

3.69 

h  1199.6 

1213.6 

1232.2 

1259.6 

1285.2 

1310.3 

1335.1 

1359.8 

1408.8 

1457.7 

240 

397.4 

v  1.92 

1.99 

2.09 

2.26 

2.42 

2.57 

2.71 

2.85 

3.13 

3.40 

, 

h  1200.9 

1215.4 

1234.3 

1261.9 

1287.6 

1312.8 

1337.6 

1362.3 

1411.5 

1460.5 

260 

404.5 

v  1.78 

1.84 

1.94 

2.10 

2.24 

2.39 

2.52 

2.65 

2.91 

3.16 

h  1202.1 

1217.1 

1236.4 

1264.1 

1289.9 

1315.1 

1340.0 

1364.7 

1414.0 

1463.2 

280 

411.2 

v  1.66 

1.72 

1.81 

1.95 

2.09 

2.22 

2.35 

2.48 

2.72 

2.95 

h  1203.1 

1218.7 

1238.4 

1266.2 

1291.9 

1317.2 

1342.2 

1367.0 

1416.4 

1465.7 

300 

417.5 

v  1.55 

1.60 

1.69 

1.83 

1.96 

2.09 

2.21 

2.33 

2.55 

2.77 

h  1204.1 

1220.2 

1240.3 

1268.2 

1294.0 

1319.3 

1344.3 

1369.2 

1418.6 

1468.0 

350 

431.9 

v  1.33 

1.38 

1.46 

1  .  58 

1.70 

1.81 

1.92 

2.02 

2.22 

2.41 

h  1206.1 

1223.9 

1244.6 

1272.7 

1298.7 

1324.1 

1349.3 

1374.3 

1424.0 

1473.7 

400 

444.8 

v  1.17 

1.21 

1.28 

1.40 

1.50 

1.60 

1.70 

1.79 

1.97 

2.14 

h  1207.7 

1227.2 

1248.6 

1276.9 

1303.0 

1328.6 

1353.9 

1379.1 

1429.0 

1478.9 

450 

456.5 

v  1.04 

1.08 

1.14 

1.25 

1.35 

1.44 

1  53 

1.61 

1.77 

1.93 

h  1209 

1231 

1252 

1281 

1307 

1333 

1358 

1383 

1434 

1484 

500 

467.3 

v  0.93 

0.97 

1.03 

1.13 

1.22 

1.31 

1.39 

1.47 

1.62 

1.76 

h  1210 

1233 

1256 

1285 

1311 

1337 

1362 

1388 

1438 

1489 

Factors  of  Evaporation. — The  figures  in  the  table  on  pp.  667-670 
are  calculated  from  the  formula  F  —  (H  —  It)  -f-  970.4,  in  which  H  is 
the  total  heat  above  32°  of  1  lb.  of  steam  of  the  observed  pressure,  li  the 
total  heat  above  32°  of  the  feed  water,  and  970.4  the  heat  of  vaporiza- 
tion, or  latent  heat,  of  steam  at  212°  F.  The  values  of  these  total 
heats  and  of  the  latent  heat  are  those  given  in  Marks  and  Davis's 
Steam  Tables. 

The  factors  are  given  for  every  3°  of  feed-water  temperature  be- 
tween 32°  and  212°,  and  for  every  5  or  10  Ibs.  steam  pressure  within 
the  ordinary  working  limits  of  pressure.  Intermediate  values  correct 
to  the  third  decimal  place  may  easily  be  found  by  interpolation. 

The  figures  given  apply  only  to  saturated  steam.  For  superheated 
steam,  factors  of  evaporation  must  be  calculated  by  the  formula,  tak- 
ing H  as  the  total  heat  of  superheated  steam  as  found  in  the  table  of 
properties  of  superheated  steam. 


FACTORS  OF  EVAPORATION. 


667 


FACTORS    OF    EVAPORATION    FOR    DUY    SATURATED    STEAM. 


Lbs. 
Gage  press.  0  .  3 
Aba.  press.  .  15 

10.3 
25 

20.3 
35 

30.3 
45 

40.3 
55 

50.3 
65 

60.3 
75 

70.3 
85 

80.3 
95 

85.3 
100 

Feed 
Water. 

FACTORS  OF  EVAPORATION. 

212°F. 

1.0003 

1.0103 

1.0169 

1.0218 

1.0258 

1.0290  1.0316 

1.0340 

1.0361 

1.0370 

209 

34 

34 

1.0200 

50 

89 

1.0321 

47 

71 

92 

1.0401 

206 

65 

65 

31 

81 

1.0320 

52 

79 

1.0402 

1  .  0423 

32 

203 

96 

96 

62 

1.0312 

51 

83 

1.0410 

33 

54 

63 

200 

1.0127 

1  .  0227 

93 

43 

82 

1.0414 

41 

64 

85 

94 

197 

58 

58 

1  .  0324 

74  1.0413 

45 

72 

95 

1.0516 

1.0525 

194 

89 

89 

55 

1.0405 

44 

76 

1.0503 

1.0526 

47 

56 

191 

1.0220 

1.0320 

86 

36 

75 

1  .  0507 

34 

57 

78 

87 

188 

51 

51 

1.0417'     67 

1.0506 

38 

65 

88 

1  .  0609 

1.0618 

185 

82 

82 

48     98 

37 

69 

96 

1.0619 

40 

49 

182 

1.0313 

1.0413 

79 

1.0529 

68 

1  .  0600 

1.0627 

50 

71 

80 

179 

44 

44 

1.0510 

60 

99 

31 

58 

81 

1  .  0702 

1.0711 

176 

75 

75 

41 

91 

1.0630 

62 

89 

1.0712 

33 

42 

173 

1.0406 

1.0506 

72 

1.0622 

61 

93 

1.0720 

43 

64 

73 

170 

37 

37 

1.0603 

53 

92 

1  .  0724 

51 

74 

95 

1.0804 

167 

68 

68 

34 

84 

1.0723 

55 

82 

1  .  0805 

1  .  0826 

35 

164 

99 

99 

65 

1.0715 

54 

86 

1.0812 

36 

57 

66 

161 

1.0530 

1.0630 

96 

85 

85 

1.0817 

43 

67 

88 

97 

158 

61 

61 

1.0727 

76 

1.0816 

47 

74 

98  1.0919 

1  .  0928 

155 

92 

92 

58 

1.0807 

46 

78 

1.0905 

1.0929 

50 

59 

152 

1.0623 

1.0723 

89 

38 

77 

1  .  0909 

36 

60 

80 

90 

149 

54 

54 

1.0820 

69 

1  .  0908 

40 

67 

91 

1.1011 

1.1021 

146 

85 

85 

51 

1.0900 

39 

71 

98 

1  .  1022 

42 

52 

143 

1.0715 

1.0815 

81 

31 

70 

1  .  1002 

1  .  1029 

52 

73 

82 

140 

46 

46 

1.0912 

62 

1  .  1001 

33 

60 

83 

1.1104 

1.1113 

137 

77 

77 

43 

93 

32 

64 

91 

1.1114 

35 

44 

134 

1.0808 

1.0908 

74!  1-1023 

63 

95 

1.1121 

45 

66 

75 

131 

39 

39 

1.1005 

54 

93 

1.1125 

52 

76 

97 

1  .  1206 

128 

70 

70 

36 

85 

1.1124 

56 

83 

1  .  1207 

1  .  1227 

37 

125 

1.0901 

1.1001 

67 

1.1116 

55 

87 

1.1214 

38 

58 

68 

122 

31 

31 

97 

47 

86 

1.1218 

45 

69 

89 

98 

119 

62 

62 

1.1128 

78 

1.1217 

49 

76 

99 

1.1320 

1  .  1329 

116 

93 

93 

59 

1  .  1209 

48 

80 

1  .  1306 

1  .  1330 

51 

60 

113 

1  .  1024 

1.1124 

90 

39 

79 

1.1310 

37 

61 

82 

91 

110 

55 

55 

1.1221 

70 

1.1309 

41 

68 

92  1.1412 

1  .  1422 

107 

86 

86 

52 

1.1301 

40 

72 

99 

1  .  1423 

43 

53 

104 

1.1116 

1.1216 

82 

32 

71 

1  .  1403 

1  .  1430 

53 

74 

83 

101 

47 

47 

1.1313 

63 

1  .  1402 

34 

61 

84 

1  .  1505 

1.1514 

98 

78 

78 

44 

93 

33 

65 

91 

1.1515 

36 

45 

95 

1  .  1209 

1  .  1309 

75 

1  .  1424 

63 

95 

1  .  1522 

46 

66 

76 

92  I 

40 

40 

1  .  1406 

55 

94 

1.1526 

53 

77 

97 

1  .  1607 

89 

71 

71 

37 

86 

1.1525 

57 

84 

1  .  1608 

1.1628 

37 

86 

1.1301 

1  .  1401 

67 

1.1518 

56 

88 

1.1615 

38 

59 

68 

83 

32 

32 

•   98 

48 

87 

1.1619 

46 

69 

90 

99 

80 

63 

63 

1.1529 

78 

1.1618 

50 

76 

1.1700 

1.1721 

1  .  1730 

77 

94 

94 

60 

1  .  1609 

48 

80 

1.1707 

31 

51 

61 

74 

1  .  1425 

1  .  1525 

91 

40 

79 

1.1711 

38 

62 

82 

92 

71 

55 

55 

1  1621 

71 

1.1710 

42 

69 

92 

1.1813 

1  .  1822 

68 

86 

86 

52 

1.1702 

41 

73 

1.1800 

1  .  1823 

44 

53 

65 

1.1517 

1.1617 

83 

33 

72 

1  .  1804 

30 

54 

75 

84 

62 

48 

48 

1.1714 

63 

1  .  1803 

35 

61 

85 

1  .  1906 

1.1915 

59 

79 

79 

45 

94 

33 

65 

92 

1.1916 

37 

46 

56 

1.1610 

1.1710 

70 

1  .  1825 

64 

96 

1  .  1923 

47 

67 

77 

53 

41 

41 

1  .  1807 

56 

95 

1.1927 

54 

78 

98 

1.2008 

50 

72 

72 

38 

87 

1.1926 

58 

85 

1.2009 

1  .  2029 

39 

47 

1.1703 

1  .  1803 

69 

1.1918 

57 

89 

1.2016 

40 

60 

70 

44 

34 

34 

1  .  1900 

49 

88 

1  .  2020 

47 

71 

91 

1.2101 

41 

65 

65 

31 

80 

1.2019 

51 

78 

1.2102 

1.2122 

32 

38 

96 

96 

62 

1.2011 

50 

82 

1.2109 

33 

53 

63 

35 

1.1827 

1.1927 

93 

42 

81 

1.2113 

40 

64 

84 

94 

32 

58 

58 

1  .  2024 

73 

1.2113 

44 

71 

95 

1.2216 

1.2225 

668 


STEAM-BOILER  ECONOMY. 


FACTORS  OF  EVAPORATION   FOR   DRY  SATURATED    STEAM. Continued. 


Gage  press.  . 
Abs.  press  .  . 

Lbs. 
90.3 
105 

95.3 
110 

100.3 
115 

105.3 
120 

110.3 
125 

115.3 
130 

120.3 
135 

125.3 
140 

130.3 
145 

135.3 
150 

140.3 
155 

Feed 
Water. 

FACTORS  OF  EVAPORATION. 

212°  F. 

1 

.0379 

1.0387 

1.0396 

1.0404 

1.0411 

1.041811.0425 

1.0431 

1.0437 

1  .  0443 

1  .  0449 

209 

1 

.0410 

1.0419 

1.0427 

35 

42 

49 

56 

62 

68 

74 

80 

206 

41 

50 

58 

66 

73 

81 

87 

93 

99 

1  .  0505 

1.0511 

203 

72 

81 

89 

97 

1.0504 

1.0512 

1.0518 

1  .  0524 

1  .  0530 

36 

43 

200 

1 

.0504 

1.0512 

1  .  0520 

1  .  0528 

35 

43 

49 

55 

61 

67 

74 

197 

35 

43 

51 

59 

66 

74 

80 

86 

92 

98 

1  .  0605 

194 

66 

74 

82 

90 

97 

1  .  0605 

1.0611 

1.0617 

1.0623 

1.0629 

36 

191 

97 

1  .  0605 

1.0613 

1.0621 

1.0629 

36 

42 

48 

54 

60 

67 

188 

1 

.0628 

36 

44 

52 

60 

67 

73 

79 

85 

91 

98 

185 

59 

67 

75 

83 

91 

98 

1  .  0704 

1.0710 

1.0716 

1.0722 

1.0729 

182 

90 

98 

1  .  0706 

1.0714 

1.0721 

1.0729 

35 

41 

47 

53 

60 

179 

1 

.0721 

1.0729 

37 

45 

52 

60 

66 

72 

78 

84 

91 

176 

52 

60 

68 

76 

83 

91 

97 

1  .  0803 

1  .  0809 

1.0815 

1.0822 

173 

82 

91 

99 

1  .  0807 

1.0814 

1.0822 

1.0828 

34 

40 

46 

53 

170 

1 

.0813 

1.0822 

1.0830 

38 

45 

53 

59 

65 

71 

77 

83 

167 

44 

53 

61 

69 

76 

84 

90 

96 

1.0902 

1  .  0908 

1.0914 

164 

75 

84 

92 

1.0900 

1.0907 

1.0914 

1.0921 

1.0927 

33 

39 

45 

161 

1 

.0906 

1.0914 

1  .  0923 

31 

38 

45 

52 

58 

64 

70 

76 

158 

37 

45 

54 

62 

69 

76 

82 

89 

95 

1.1001 

1.1007 

155 

68 

76 

85 

93 

1  .  1000 

1  .  1007 

1.1013 

1.1020 

1.1026 

32 

38 

152 

99 

1.1007 

1.1015 

1  .  1024 

31 

38 

44 

51 

57 

63 

69 

149 

1 

.1030 

38 

46 

55 

62 

69 

75 

81 

88 

94 

1.1100 

146 

61 

69 

77 

86 

93 

1.1100 

1.1106 

1.1112 

1.1119 

1.1125 

31 

143 

92 

1.1100 

1.1108 

1.1116 

1.1124 

31 

37 

43 

49 

56 

62 

140 

1 

.1123 

31 

39 

47 

54 

62 

68 

74 

80 

86 

93 

137 

53 

62 

70 

78 

85 

93 

99 

1  .  1205 

1.1211 

1.1217 

1  .  1224 

134 

84 

93 

1.1201 

1  .  1209 

1.1216 

1.1223 

1.1230 

36 

42 

48 

54 

131 

1 

.1215 

1.1223 

32 

40 

47 

54 

60 

67 

73 

79 

85 

128 

46 

54 

62 

71 

78 

85 

91 

98 

1  .  1304 

1.1310 

1.1316 

125 

77 

85 

93 

1  .  1302 

1  .  1309 

1.1316 

1.1322 

1  .  1328 

35 

41 

47 

122 

1 

.1308 

1.1316 

1  .  1324 

32 

40 

47 

53 

59 

65 

71 

78 

119 

39 

47 

55 

63 

70 

78 

84 

90 

96 

1  .  1402 

1.1409 

116 

69 

78 

86 

94 

1  .  1401 

1  .  1408 

1.1415 

1.1421 

1  .  1427 

33 

39 

113 

1 

.1400 

1  .  1408 

1.1417 

1  .  1425 

32 

39 

45 

52 

58 

64 

70 

110 

31 

39 

47 

56 

63 

70 

76 

82 

89 

95 

1.1501 

107 

62 

70 

78 

87 

94 

1.1501 

1.1507 

1.15131.1519 

1.1526 

32 

104 

92 

1.1501 

1  .  1509 

1.1517 

1  .  1525 

32 

38 

44 

50 

56 

63 

101 

1 

.1523 

32 

40 

48 

55 

63 

69 

75 

81 

87 

93 

98 

54 

62 

71 

79 

86 

93 

1  .  1600 

1.1606 

1.1612 

1.1618 

1.1624 

95 

85 

93 

1.1602 

1.1610 

1.1617 

1  .  1624 

30 

37 

43 

49 

55 

92 

1 

.1616 

1  .  1624 

32 

41 

48 

55 

61 

67 

74 

80 

86 

89 

47 

55 

63 

71 

79 

86 

92 

98 

1.1704 

1.1711 

1.1717 

86 

78 

86 

94 

1.1702 

1.1710 

1.1717 

1.1723 

1.1729 

35 

41 

48 

83 

1 

.1708 

1.1717 

1.1725 

33 

40 

48 

54 

60 

66 

72 

78 

80 

39 

47 

56 

64 

71 

78 

85 

91 

97 

1.1803 

1  .  1809 

77 

70 

78 

86 

95 

1  .  1802 

1  .  1809 

1.1815 

1.1822 

1.1828 

34 

40 

74 

1 

.1801 

1.1S09 

1.1817 

1.1826 

33 

40 

46 

52 

59 

65 

71 

71 

32 

40 

48 

56 

64 

71 

77 

83 

89 

96 

1  .  1902 

68 

62 

71 

79 

87 

94 

1  .  1902 

1  .  1908 

1.1914 

1  .  1920 

1.1926 

33 

65 

93 

1  .  1902 

1.1910 

1.1918 

1.1925 

33 

39 

45 

51 

57 

68 

62 

1 

.1924 

32 

41 

49 

56 

63 

70 

76 

82 

88 

94 

59 

55 

63 

72 

80 

87 

94 

1.2000 

1  .  2007 

1.2013 

1.2019 

1.2025 

56 

86 

94 

1.2002 

1.2011 

1.2018 

1.2025 

1   31 

38 

44 

50 

56 

53 

1 

.2017 

1.2025 

33 

42 

49 

56 

62 

68 

75 

81 

87 

50 

48 

56 

64 

73 

80 

87 

93 

99 

1.2106 

1.2112 

1.2118 

47 

79 

87 

95 

1.2104 

1.2111 

1.2118 

1.2124 

1.2130 

37 

43 

49 

44 

1 

.2110 

1.2118 

1.2126 

35 

42 

49 

55 

61 

68 

74 

80 

41 

41 

49 

57 

66 

73 

80 

86 

92 

99 

1  .  2205 

1.2211 

38 

72 

80 

88 

97 

1  .  2204 

1.2211 

1.2217 

1.2223 

1.2230 

36 

42 

35 

1.2203 

1.2211 

1.2219 

1.2228 

35 

42 

48 

55 

61 

67 

73 

32 

34 

42 

51 

59 

66 

73 

79 

86 

92 

98 

1.2340 

FACTORS  OF  EVAPORATION. 


669 


FACTORS    OF   EVAPORATION  FOR  DRY    SATURATED   STEAM. — Continued. 


Lbs, 
Gage  press.  .  145  .  3 
Abs.  press.  .  160 

150.3 
165 

155.3 
170 

160.3 
175 

165.3 
180 

170.3 
185 

175.3 
190 

180.3 
195 

185.3 
200 

190.3 
205 

195.3 
210 

Feed 
Water. 

FACTORS  OF  EVAPORATION. 

212°  F. 

1  .  0454 

1  .  0460 

1.0464 

1.0469 

1  .  0474 

1.0478 

1  .  0483 

1  .  0487 

1.0492  1.0496 

1  .  0499 

209 

86 

91 

95 

1.0500 

1  .  0505 

1.0509 

1.0514 

1.0519 

1.05231.0527 

1.0530 

206 

1.0517 

1  .  0522 

1.0526 

31 

36 

40 

45 

50 

54    58 

61 

203 

•  48 

53 

57 

62 

67 

71 

77 

81 

85 

89 

92 

200 

79 

84 

88 

93 

98 

1.0602 

1.0608 

1.0612 

1.0616 

1  .  0620 

1.0623 

197 

1.0610 

1.0615 

1.0619 

1  .  0624 

1  .  0629 

33 

39 

43 

47 

51 

54 

194 

41 

46 

50 

55 

60 

64 

70 

74 

78 

82 

85 

191 

72 

77 

81 

86 

91 

95 

1.0701 

1.0705 

1.0709 

1.0713 

1.0716 

188 

1.0703 

1.0708 

1.0712 

1.0717 

1.0722 

1.0727 

32 

36 

40 

44 

47 

185 

34 

39 

43 

48 

53 

58 

63 

67 

71 

75 

78 

182 

65 

70 

74 

79 

84 

88 

94 

98 

1.0802 

1.0806 

1.0809 

179 

96 

1.0801 

1  .  0805 

1.0810 

1.0815 

1.0819 

1.0825 

1.0829 

33 

37 

40 

176 

1.0827 

32 

36 

41 

46 

50 

56 

60 

64 

68 

71 

173 

58 

63 

67 

72 

'77 

81 

87 

91 

95 

99 

1.0902 

170 

89 

94 

98 

1.0903 

1.0908 

1.0912 

1.0917 

1  .  0922 

1.0926 

1.0930 

33 

167 

1.0920 

1.0925 

1  .  0929 

34 

39 

43 

48 

53 

57 

61 

64 

164 

51 

56 

60 

65 

70 

74 

79 

84 

88 

92 

95 

161 

81 

87 

91 

96 

1.1001 

1  .  1005 

1.1010 

1.1014 

1.1019 

1.1023 

1.1026 

158 

1.1012 

1.1018 

1  .  1022 

1  .  1027 

32 

36 

41 

45 

49 

54 

57 

155 

43 

48 

53 

58 

63 

67 

72 

76 

80 

85 

88 

152 

74 

79 

83 

89 

94 

98 

1.1103 

1.1107 

1.1111 

1.1115 

1.1119 

149 

1.1105 

1.1110 

1.1114 

1.1120 

1.1125 

1.1129 

34 

38 

42 

46 

49 

146 

36 

41 

45 

50 

56 

60 

65 

69 

73 

77 

80 

143 

67 

72 

76 

81 

86 

91 

96 

1.1200 

1  .  1204 

1.1208 

1.1211 

140 

98 

1  .  1203 

1.1207 

1.1212 

1.1217 

1.1221 

1.1227 

31 

35 

39 

42 

137 

1  .  1229 

34 

38 

43 

48 

52 

58 

62 

66 

70 

73 

134 

59 

65 

69 

74 

79 

83 

88 

92 

97 

1.1301 

1  .  1304 

131 

90 

95 

1.1300 

1  .  1305 

1.1310 

1.1314 

1.1319 

1.1323 

1.1327 

32 

35 

128 

1.1321 

1.1326 

30 

36 

41 

45 

50 

54 

58 

62 

66 

125 

52 

57 

61 

66 

72 

76 

81 

85 

89 

93 

96 

122 

83 

88 

92 

97 

1  .  1402 

1  .  1407 

1.1412 

1.1416 

1  .  1420 

1  .  1424 

1  .  1428 

119 

1.1414 

1.1419 

1  .  1423 

1  .  1428 

33 

37 

43 

47 

51 

55 

57 

116 

45 

50 

54 

59 

61 

68 

73 

78 

82 

86 

89 

113 

75 

81 

85 

90 

95 

99 

1  .  1504 

1.1508 

1.1512 

1.1515 

1.1520 

110 

1.1506 

1.1511 

1.1515 

1.1521 

1.1526 

1  .  1530 

35 

39 

43 

47 

50 

107 

37 

42 

46 

51 

57 

61 

66 

70 

74 

78 

81 

104 

68 

73 

77 

82 

87 

92 

97 

1.1601 

1  .  1605 

1.1609 

1.1612 

101 

99 

1.1604 

1.1608 

1.1613 

1.1618 

1.1622 

1.1627 

32 

36 

40 

43 

98 

1  .  1629 

35 

39 

44 

49 

53 

58 

62 

67 

71 

74 

95 

60 

65 

70 

75 

80 

84 

89 

93 

97 

1.1701 

1.1705 

92 

91 

96 

1.1700 

1  .  1705 

1.1711 

1.1715 

1.1720 

1  .  1724 

1  .  1728 

32 

35 

89 

1.1722 

1.1727 

31 

36 

42 

46 

51 

55 

59 

63 

66 

86 

53 

58 

62 

67 

72 

76 

82 

86 

90 

94 

97 

83 

84 

89 

93 

98 

1  .  1803 

1  .  1807 

1.1812 

1.1817 

1.1821 

1.1825 

1.1828 

80 

1.1814 

1.1820 

1.1824 

1.1829 

34 

38 

43 

47 

52 

56 

59 

77 

45 

50 

54 

60 

65 

69 

74 

78 

82 

86 

90 

74 

76 

81 

85 

90 

96 

1  .  1900 

1  .  1905 

1  .  1909 

1.1913 

1.1917 

1.1920 

71 

1  .  1907 

1.1912 

1.1916 

1.1921 

1.1926 

31 

36 

40 

44 

48 

51 

68 

38 

43 

47 

52 

57 

61 

67 

71 

75 

79 

82 

65 

69 

74 

78 

83 

88 

92 

97 

1  .  2002 

1.2006 

1.2010 

1.2013 

62 

99 

1  .  2005 

1.2009 

1.2014 

1.2019 

1.2023 

1  .  2028 

32 

36 

41 

44 

59 

1  .  2030 

35 

40 

45 

50 

54 

59 

63 

67 

72 

75 

56 

61 

66 

70 

76 

81 

85 

90 

94 

98 

1.2102 

1.2106 

53 

92 

97 

1.2101 

1.2107 

1.2112 

1.2116 

1.2121 

1.2125 

1.2129 

33 

36 

50 

1.2123 

1.2128 

32 

37 

43 

47 

52 

56 

60 

64 

67 

47 

54 

59 

63 

68 

74 

78 

83 

87 

91 

95 

98 

44 

85 

90 

94 

1.2200 

1.2205 

1  .  2209 

1.2214 

1.2218 

1  .  2222 

1.2226 

1  .  2229 

41 

1.2216 

1.2221 

1  .  2225 

31 

36 

40 

45 

49 

53 

57 

60 

38 

47 

52 

56 

62 

67 

71 

76 

80 

84 

88 

91 

35 

78i     83 

88 

93 

98 

1  .  2302 

1  .  2307 

1.2311 

1.2315 

1  .  2320 

1.2323 

32      1.2309!  1.2315 

1.2319 

1  .  2324 

1  .  2329 

33 

38 

42 

46 

51 

54 

670 


STEAM-BOILER  ECONOMY. 


FACTORS   OF   EVAPORATION   FOR   DRY   SATURATED   STEAM. — Continued. 


Lbs. 
Gage  press.  .  200  .  3 
Abs.  press.  .215 

205.3   210.3 
220    J225 

215.3 
230 

220.3 
235 

225.3 
240 

230.3 
245 

235.3 
250 

240.3 
255 

245.3 
260 

250.3 
265 

Feed 
Water. 

FACTORS  OF  EVAPORATION. 

212°  F. 

1  .  0503 

1.0507 

1.0510 

1.0513 

1.0517 

1  .  0520 

1.0523 

1  .  0527 

1.0529 

1  .  0533 

1.0535 

209 

34 

38 

41 

44 

48 

52 

55 

58 

60 

64 

66 

206 

65 

69 

72 

75 

79 

83 

86 

89 

91 

95 

97 

203 

96 

1.0600 

1.0603 

1.0606 

1.0611 

1.0614 

1.0617 

1.0620 

1.0622 

1.0626 

1.0629 

200 

1.0627 

31 

34 

37 

42 

45 

48 

51 

53 

57 

60 

197 

58 

62 

65 

68 

73 

76 

79 

82 

84 

88 

91 

194 

89 

93 

96 

1  .  0700 

1  .  0704 

1.0707 

1.0710 

1.0713 

1.0715 

1.0719 

1.0722 

191 

1.0720 

1.0724 

1.0727 

31 

35 

38 

41 

44 

46 

50 

53 

188 

51 

55 

58 

62 

66 

69 

72 

75 

78 

81 

84 

185 

82 

86 

89 

93 

97 

1.0800 

1.0830 

1  .  0806 

1.0809 

1.0812 

1.0816 

182 

1.0813 

1.0817 

1.0820 

.0823 

.0828 

31 

34 

37 

39 

43 

45 

179 

44 

48 

51 

54 

59 

62 

65 

68 

70 

74    77 

176 

75 

79 

82 

86 

90 

93    96 

99 

1.0901 

1.090511.0908 

173 

1.0906 

1.0910 

1.0913 

.0916 

.0921 

1.0924 

1.0927 

1.0930 

32 

36 

39 

170 

37 

41 

44 

47 

51 

55 

58 

61 

63 

67 

69 

167 

68 

72 

75 

78 

82 

86 

89 

92 

94 

98 

1.1001 

164 

99 

1  .  1003 

1  .  1006 

.1009 

1.1013 

1.1016 

1.1019 

1  .  1023 

1  .  1025 

1  .  1029 

31 

161 

1  .  1030 

34 

37 

40 

44 

47 

50 

54 

56 

60 

62 

158 

61 

65 

68 

71 

75 

78 

81 

85 

87 

91 

93 

155 

92 

96 

99 

.1102 

1.1106 

1.1109 

1.1112 

1.1115 

1.1118 

1.1122 

1.1124 

152 

1.1123 

1.1127 

1.1130 

33 

37 

40 

43 

46 

49 

53 

55 

149 

54 

58 

61 

64 

68 

71 

74 

77 

80 

83 

86 

146 

84 

89 

92 

95 

99 

1  .  1202 

1.1205 

1  .  1208 

1.1211 

1.1214 

1.1217 

143 

1.1215 

1.1219 

1.1223 

1.1226 

1.1230 

33 

36 

39 

42 

45 

48 

140 

46 

50 

53 

56 

61 

64 

67 

70 

72 

76 

79 

137 

77 

81 

84 

87 

92 

95 

98 

1.1301 

1.1303 

1.1307 

1.1310 

134 

1  .  1308 

1.1312 

1.1315 

1.1318 

1.1322 

1.1326 

1.1329 

32 

34 

38 

40 

131 

39 

43 

46 

49 

53 

56 

59 

62 

65 

69 

71 

128 

70 

74 

77 

80 

84 

87 

90 

93 

96 

1  .  1400 

1  .  1402 

125 

1.1400 

1  .  1405 

1  .  1408 

1.1411 

1.1415 

1.1418 

1.1421 

1  .  1424 

1.1427 

30 

33 

122 

31 

35 

39 

42 

46 

49 

52 

55 

58 

61 

64 

119 

62 

66 

69 

72 

77 

80 

83 

86 

88 

92 

95 

116 

93 

97 

1  .  1500 

1  .  1503 

1  .  1507 

1.1511 

1.1514 

1.1517 

1.1519 

1.1523 

1.1525 

113 

1  .  1524 

1.1528 

31 

34 

38 

41 

44 

48 

50 

54 

56 

110 

55 

59 

62 

65 

69 

72 

75 

78 

81 

85 

87 

107 

85 

90 

93 

96 

1  .  1600 

1.1603 

1.1606 

1.1609 

1.1612 

1.1615 

1.1618 

104 

1.1616 

1.1620  1.1624 

1.1627 

31 

34 

37 

40 

43 

46 

49 

101 

47 

51 

54 

57 

61 

65 

68 

71 

73 

77 

80 

98 

78 

82 

85 

88 

92 

95 

98 

1.1702 

1.1704 

1.1708 

1.1710 

95 

1  .  1709 

1.1713 

1.1716 

1.1719 

1.1723 

1.1726 

1.1729 

32 

35 

39 

41 

92 

39 

44 

47 

50 

54 

57 

60 

63 

66 

69 

72 

89 

70 

75 

78 

81 

85 

88 

91 

94 

97 

1  .  1800 

1  .  1803 

86 

1.1801 

1  .  1805 

1  .  1808 

1.1812 

1.1816 

1.1819 

1.1822 

1  .  1825 

1.1827 

31 

34 

83 

32 

36 

39 

42 

46 

50 

53 

56 

58 

62 

64 

80 

63 

67 

70 

73 

77 

80 

83 

87 

89 

93 

95 

77 

94 

98 

1.1901 

1  .  1904 

1  .  1908 

1.1911 

1.1914 

1.1917 

1.1920 

1.1924 

1.1926 

74 

1  .  1924 

1  .  1929 

32 

35 

39 

42 

45 

48 

51 

54 

57 

71 

55 

59 

63 

66 

70 

73 

76 

79 

82 

85 

88 

68 

86 

90 

93 

96 

1  .  2001 

1.2004 

1.2007 

1.2010 

1.2012 

1.2016 

1.2019 

65 

1.2017 

1  .  2021 

1.2024 

1  .  2027 

31 

35 

38 

41 

43 

47 

49 

62 

48 

52 

55 

58 

62 

65 

68 

72 

74 

78 

80 

59 

79 

8c 

86 

89 

93 

96 

99 

1.2102 

1.2105 

1.2109 

1.2111 

56 

1.2110 

1.2114 

1.2117 

1.2120 

1.2124 

1.2127 

1.2130 

33 

36 

40 

42 

53 

41 

45 

48 

51 

55 

58 

61 

64 

67 

70 

73 

50 

71 

7e 

79 

82 

86 

89 

92 

95 

98 

1  .  2201 

1  .  2204 

47 

1.2202 

1.2207 

1.2210 

1.2213 

1.2217 

1  .  2220 

1.2223 

1  .  2226 

1  .  2229 

32 

35 

44 

34 

38 

41 

44 

48 

51 

54 

57 

60 

63 

66 

41 

65 

6£ 

72 

75 

79 

82 

85 

88 

91 

94 

97 

38 

9e 

1  .  230C 

1  .  2303 

1  .  2306 

1.2310 

1.2313 

1.2316 

1.2319 

1  .  2322 

1  .  2325 

1  .  2328 

35 

1  .  232" 

31     34 

37 

41 

44 

47 

50 

53 

59 

32 

58 

62    6, 

68 

72 

75 

78 

82 

^84 

88 

90 

CHIMNEYS.  671 


Chimney-draft  Theory.— The  commonly  accepted  theory  of  chim- 
ney-draft, based  on  Peclet's  and  Rankine's  hypotheses  (see  Rankine's 
Steam-engine),  is  discussed  by  Prof.  De  Volson  Wood  in  Trans. 
A.  S.  M.  E.,  vol.  xi. 

Peclet  represented  the  law  of  draft  by  the  formula 


in  which  h  is  the  "head,"  defined  as  such  a  height  of  hot  gases  as,  if 
added  to  the  column  of  gases  in  the  chimney,  would 
produce  the  same  pressure  at  the  furnace  as  a  column  of 
outside  air,  of  the  same  area  of  base,  and  a  height  equal 
to  that  of  the  chimney; 

u  is  the  required  velocity  of  gases  in  the  chimney; 

G  a  constant  to  represent  the  resistance  to  the  passage  of  air 
through  the  coal; 

I  the  length  of  the  flues  and  chimney ; 

ra  the  mean  hydraulic  depth,  or  the  area  of  a  cross-section 
divided  by  the  perimeter ; 

/  a  constant  depending  upon  the  nature  of  the  surfaces  over 
which  the  gases  pass,  whether  smooth,  or  sooty  and 
rough. 

Rankine's   formula    (Steam-engine,   p.   288),   derived   by   giving 
certain  values  to  the  constants  (so-called)  in  Peclet's  formula,  is 


-°  (0.0807)  .  , 

H  -  H  =  (0.96-  -  1)#; 
\       TI        J 


-(0.084) 


in  which  H  =  the  height  of  the  chimney  in  feet; 

TO  =  493°  F.,  absolute  (temperature  of  melting  ice)  ; 
TI  =  absolute  temperature  of  the  gases  in  the  chimney; 
Ta  =  absolute  temperature  of  the  external  air. 

Prof.  Wood  derives  from  this  a  still  more  complex  formula  which 
gives  the  height  of  chimney  required  for  burning  a  given  quantity  of 
coal  per  second,  and  from  it  he  calculates  the  following  table,  showing 
the  height  of  chimney  required  to  burn  respectively  24,  20,  and  16 
Ibs.  of  coal  per  sq.  ft.  of  grate  per  hour,  for  the  several  temperatures 
of  the  chimney-gases  given. 

Rankine's  formula  gives  a  maximum  draft  when  T  =  21/12x2,  or 
622°  F.,  when  the  outside  temperature  is  60°.  Prof.  Wood  says: 


672 


STEAM-BOILER  ECONOMY. 


"This  result  is  not  a  fixed  value,  but  departures  from  theory  in  prac- 
tice do  not  affect  the  result  largely.  There  is,  then,  in  a  properly 
constructed  chimney,  properly  working,  a  temperature  giving  a 
maximum  draft,*  and  that  temperature  is  not  far  from  the  value 
given  by  Rankine,  although  in  special  cases  it  may  be  50°  or  75° 
more  or  less." 


Chimney-gas. 

Coal  per  Square  Foot  of  Grate~per  Hour,  Ibs. 

Outside  Air, 

24 

20 

16 

TJ 

n 

Temperature, 

Absolute. 

Fahrenheit. 

Height  H,  Feet. 

520° 

700 

239 

250.9 

157.6 

67.8 

Absolute,  or 

800 

339 

172.4 

115.8 

55.7 

59°  F. 

1000 

539 

149.1 

100.0 

48.7 

1100 

639 

148.8 

98.9 

48.2 

1200 

739 

152.0 

100.9 

49.1 

1400 

939 

159.9 

105.7 

51.2 

1600 

1139 

168.8 

111.0 

53.5 

2000 

1539 

206.5 

132.2 

63.0 

All  attempts  to  base  a  practical  formula  for  chimneys  upon  the 
theoretical  formulae  of  Peclet  and  Rankine  have  failed  on  account  of 
the  impossibility  of  assigning  correct  values  to  the  so-called  "con- 
stants" G  and  /."  (See  Trans.  A.  S.  M.  E.,  xi.  984.) 

Force  or  Intensity  of  Draft. — The  force  of  the  draft  is  equal  to 
the  difference  between  the  weight  of  the  column  of  hot  gases  inside 
of  the  chimney  and  the  weight  of  a  column  of  the  external  air  of  the 
same  height.  It  is  measured  by  a  draft-gage,  usually  a  U-tube 
partly  filled  with  water,  one  leg  connected  by  a  pipe  to  the  interior  of 
the  flue,  and  the  other  open  to  the  external  air. 

If  D  is  the  density  of  the  air  outside,  d  the  density  of  the  hot  gas 
inside,  in  Ibs.  per  cu.  ft.,  h  the  height  of  the  chimney  in  feet,  and  0.192 
the  factor  for  converting  pressure  in  Ibs.  per  sq.  ft.  into  inches  of 
water-column,  then  the  formula  for  the  force  of  draft  expressed  in 
inches  of  water  is, 

F  =  0.192h(D  -  d). 


*  Much  confusion  to  students  of  the  theory  of  chimneys  has  resulted  from 
their  understanding  the  words  maximum  draft  to  mean  maximum  intensity  or 
pressure  of  draft,  as  measured  by  a  draft-gage.  It  here  means  maximum  quantity 
or  weight  of  gases  passed  up  the  chimney.  The  maximum  intensity  is  found 
only  with  maximum  temperature,  but  after  the  temperature  reaches  about 
622°  F.  the  density  of  the  gas  decreases  more  rapidly  than  its  velocity  increases, 
so  that  the  weight  is  a  maximum  about  622°  F.,  as  shown  by  Rankine. 


CHIMNEYS.  673 

The  density  varies  with  the  absolute  temperature  (see  Eankine). 

d  =  -0.084;     D  =  0.0807-°, 
TI  T* 

where  TO  is  the  absolute  temperature  at  32°  F.,  =  493,  TI  the  absolute 
temperature  of  the  chimney-gases,  and  r%  that  of  the  external  air. 
Substituting  these  values  the  formula  for  force  of  draft  becomes 


_  4Ul\  _  hHM  _  1M\ 

Ti     /  \    Ti  Ti    / 


To  find  the  maximum  intensity  of  draft  for  any  given  chimney, 
the  heated  column  being  600°  F.,  and  the  external  air  60°,  multiply 
the  height  above  grate  in  feet  by  .0073,  and  the  product  is  the  draft 
in  inches  of  water. 


HEIGHT    OF    WATER    COLUMN    DUE    TO    UNBALANCED    PRESSURE    IN    CHIMNEY 

100  FEET  HIGH.     (The  Locomotive,  1884.) 


o-Sg 

rl 

H     0 

A  cuijjci  auuj  c  vi    »u«  iHAijci  juc*i  mi  j_»ai  ^nj.ctc-1  1    j.i.*    iftSB*  V^*   o^no-ic   m,uuu« 

0° 

10° 

20° 

30° 

40° 

50° 

60° 

70° 

80° 

90° 

100° 

200 

.453 

.419 

.384 

.353 

.321 

.292 

.263 

.234 

.209 

.182 

.157 

220 

.488 

.453 

.419 

.388 

.355 

.326 

.298 

.269 

.244 

.217 

.192 

240 

.520 

.488 

.451 

.421 

.388 

.359 

.330 

.301 

.276 

.250 

.225 

260 

.555 

.528 

.484 

.453 

.420 

.392 

.363 

.334 

.309 

.282 

.257 

280 

.584 

.549 

.515 

.482 

.451 

.422 

.394 

.365 

.340 

.313 

.288 

300 

.611 

.576 

.541 

.511 

.478 

.449 

.420 

.392 

.367 

.340 

.315 

320 

.637 

.603 

.568 

.538 

.505 

.476 

.447 

.419 

.394 

.367 

.342 

340 

.662 

.638 

.593 

.563 

.530 

.501 

.472 

.443 

.419 

.392 

.367 

360 

.687 

.653 

.618 

.588 

.555 

.526 

.497 

.468 

.444 

.417 

.392 

380 

.710 

.676 

.641 

.611 

.578 

.549 

.520 

.492 

.467 

.440 

:415 

400 

.732 

.697 

.662 

.632 

.598 

.570 

.541 

.513 

.488 

.461 

.436 

420 

.754 

.718 

.684 

.653 

.620 

.591 

.563 

.534 

.509 

.482 

.457 

440 

.773 

.739 

.705 

.674 

.641 

.612 

.584 

.555 

.530 

.503 

.478 

460 

.793 

.758 

.724 

.694 

.660 

.632 

.603 

.574 

.549 

.522 

.497 

480 

.810 

.776 

.741 

.710 

.678 

.649 

.620 

.591 

.566 

.540 

.515 

500 

.829 

.791 

.760 

.730 

.697 

.669 

.639 

.610 

.586 

.559 

.534 

For  any  other  height  of  chimney  than  100  ft.  the  height  of  water- 
column  is  found  by  simple  proportion,  the  height  of  water-column 
being  directly  proportional  to  the  height  of  chimney. 

The  calculations  have  been  made  for  a  chimney  100  ft.  high,  with 
various  temperatures  outside  and  inside  of  the  flue,  and  on  the  sup- 
position that  the  temperature  of  the  chimney  is  uniform  from  top  to 
bottom.  This  is  the  basis  on  which  all  calculations  respecting  the 
draft-power  of  chimneys  have  been  made  by  Eankine  and  other  writers, 


674 


STEAM-BOILER  ECONOMY. 


but  it  is  very  far  from  the  truth  in  most  cases.  The  difference  will 
be  shown  by  comparing  the  reading  of  the  draft-gage  with  the  table 
given.  In  one  case  a  chimney  122  ft.  high  showed  a  temperature 
at  the  base  of  320°,  and  at  the  top  of  230°. 

Box,  in  his  "Treatise  on  Heat,"  gives  the  following  table : 

DRAFT  POWERS  OF  CHIMNEYS,  ETC.,  WITH  THE  INTERNAL  AIR  AT    552°  AND 
THE    EXTERNAL   AIR    AT    62°,    AND    WITH    THE    DAMPER    NEARLY    CLOSED. 


0>>^ 

l-s 

Theoretical  Velocity, 

*o  >>^ 

^"o    . 

Theoretical  Velocity, 

~s  §  8 

O        M 
(X,  go  « 

in  Feet  per  Second. 

*>  c  o> 

O         _     >H 

in  Feet  per  Second. 

M  Sf*< 

'53 

^  * 

!§|fe 

JS^I 

Wo.  9 

2-2 

Cold  Air 

Hot  Air 

wO.2 

S-2 

Cold  Air 

Hot  Air 

Q 

Entering. 

at  Exit. 

O 

Entering. 

at   Exit. 

10 

.073 

17.8 

35.6 

80 

.585 

50.6 

101.2 

20 

.146 

25.3 

50.6 

90 

.657 

53.7 

107.4 

30 

.219 

31.0 

62.0 

100 

.730 

56.5 

113.0 

40 

.292 

35.7 

71.4 

120 

.876 

62.0 

124.0 

50 

.365 

40.0 

80.0 

150 

1.095 

69.3 

138.6 

60 

.438 

43.8 

87.6 

175 

1.277 

74.3 

149.6 

70 

.511 

47.3 

94.6 

200 

1.460 

80.0 

160.0 

Bate  of  Combustion  Due  to  Height  of  Chimney. — Trowbridge's 
"Heat  and  Heat-engines"  gives  the  following  table  showing  the  heights 
of  chimney  for  producing  certain  rates  of  combustion  per  sq.  ft.  of 
section  of  the  chimney.  It  may  be  approximately  true  for  anthracite 
in  moderate  and  large  sizes,  but  greater  heights  than  are  given  in 
the  table  are  needed  to  secure  the  given  rates  of  combustion  with 
small  sizes  of  anthracite,  and  for  bituminous  coal  smaller  heights  will 
suffice  if  the  coal  is  reasonably  free  from  ash — 5  per  cent  or  less. 


Lbs.  of  Coal 

Lbs.  of  Coal 

Lbs.  of  Coal 

Burned  per 

Lbs.  of  Coal 

Burned  per 

Heights 
in 
Feet. 

Burned  per 
Hour  per 
Square  Foot 
of  Section 

Square  Foot 
of  Grate,  the 
Ratio  of  Grate 
to  Section  of 

Heights 
in 
Feet. 

Burned  per 
Hour  per 
Square  Foot 
of  Section 

Square  Foot 
of  Grate,  the 
Ratio  of  Grate 
to  Section  of 

of  Chimney. 

Chimney 

of  Chimney. 

Chimney 

being  8  to  1. 

being  8  to  1. 

20 

60 

7.5 

70 

126 

15.8 

25 

68 

8.5 

75. 

131 

16.4 

30 

76 

9.5 

80 

135 

16.9 

35 

84 

10.5 

85 

139 

17.4 

40 

93 

11.6 

90 

144 

18.0 

45 

99 

12.4 

95 

148 

18.5 

50 

105 

13.1 

100 

152 

19.0 

55 

111 

13.8 

105 

156 

19.5 

60 

116 

14.5 

110 

160 

20.0 

65 

121 

15.1 

Thurston's  rule  for  rate  of  combustion  effected  by  a  given  height 
of  chimney  (Trans.  A.  S.  M.  E.,  xi.  991)  is:  Subtract  1  from  twice 
the  square  root  of  the  height  and  the  result  is  the  rate  of  combustion 


CHIMNEYS. 


675 


in  pounds  per  square  foot  of  grate  per  hour,  for  anthracite.  Or  rate 
=  2  \/h — 1,  in  which  h  is  the  height  in  feet.  This  rule  gives  the 
following : 


h=    50  60  70  80  90 

2>/A_i=i3.i4      14.49      15.73      16.89     17.97 


100 
19 


110    125    150    175     200 
19.97  21.36  23.49  25.45   27.28 


The  results  agree  closely  with  Trowbridge's  table  given  above.  In 
practice  the  high  rates  of  combustion  for  high  chimneys  given  by  the 
formula  are  not  generally  obtained,  for  the  reason  that  with  high 
chimneys  there  are  usually  long  horizontal  flues  serving  many  boilers, 
and  the  friction  and  the  interference  of  currents  from  the  several 
boilers  are  apt  to  cause  the  intensity  of  draft  in  the  branch  flues  lead- 
ing to  each  boiler  to  be  much  less  than  that  at  the  base  of  the 
chimney.  The  draft  of  each  boiler  is  also  usually  restricted  by  a 
damper  and  by  bends  in  the  gas-passages.  In  a  battery  of  several 
boilers  connected  to  a  chimney  150  ft.  high,  the  author  found  a  draft 
of  %-in.  water-column  at  the  boiler  nearest  the  chimney,  and  only 
i^-in.  at  the  boiler  farthest  away.  The  first  boiler  was  wasting  fuel 
from  too  high  temperature  of  the  chimney-gases,  900°,  having  too 
large  a  grate-surface  for  the  draft,  and  the  last  boiler  was  working 
below  its  rated  capacity  and  with  poor  economy,  on  account  of  insuffi- 
cient draft. 

The  effect  of  changing  the  length  of  the  flue  leading  into  a 
chimney  60  ft.  high  and  2  ft.  9  ins.  square  is  given  in  the  following 
table,  from  Box  on  "Heat" : 


Length  of  Flue  in  Feet. 

Horse-power. 

Length  of  Flue  in  Feet. 

Horse-power. 

50 

107.6 

800 

56.1 

100 

100.0 

1000 

51.4 

200 

85.3 

1500 

43.3 

400 

70.8 

2000 

38.2 

600 

62.5 

3000 

31.7 

The  temperature  of  the  gases  in  this  chimney  was  assumed  to  be 
552°  F.,  and  that  of  the  atmosphere  62°. 

Height  of  Chimney  Required  for  Different  Fuels, — The  minimum 
height  necessary  varies  with  the  fuel,  wood  requiring  the  least,  then 
good  bituminous  coal,  and  fine  sizes  of  anthracite  the  greatest.  It 
also  varies  with  the  character  of  the  boiler — the  smaller  and  more 
circuitous  the  gas-passages  the  higher  the  stack  required;  also  with 
the  number  of  boilers,  a  single  boiler  requiring  less  height  than  several 
that  discharge  into  a  horizontal  flue.  No  general  rule  can  be  given. 

C.  L.  Hubbard  (Am,.  Electrician,  Mar.,  1904)  says:  The  following 
heights  have  been  found  to  give  good  results  in  plants  of  moderate  size, 
and  to  produce  sufficient  draught  to  force  the  boilers  from  20  to  30  per 
cent  above  their  rating : 


676 


STEAM-BOILER  ECONOMY. 


With  free-burning  bituminous  coal,  75  feet;  with  anthracite  of 
medium  and  large  size,  100  feet ;  with  slow-burning  bituminous  coal, 
120  feet;  with  anthracite  pea  coal,  130  feet;  with  anthracite  buckwheat 
coal,  150  feet.  For  plants  of  700  or  800  horse-power  and  over,  the 
chimney  should  not  be  less  than  150  feet  high  regardless  of  the  kind  of 
coal  to  be  used. 

Temperatures  at  Different  Heights  in  Chimneys. — Peabody  and 
Miller  (Steam  Boilers,  page  199)  give  the  chart  which  is  herewith 
reproduced  (Fig.  278)  showing  the  temperatures  that  were  found 

at  different  heights  in  three  chim- 
neys. A  was  an  unlined  steel  stack, 
3  ft.  diam.,  100  ft.  high.  B  was  a  brick 
stack  3  ft.  square,  102  ft.  high.  C  and 
D  are  the  same  stack,  a  250-ft.  Cus- 
tody radial  brick,  18  ft.  internal 
diameter  at  bottom  and  16  ft.  at  top. 
The  temperature  of  the  gas  entering 
the  stack  was  much  higher  in  the  series 
of  tests  shown  by  curve  C  than  in  those 
shown  by  curve  D.  The  curve  A,  of 
the  steel  stack,  shows  a  much  more 
rapid  diminution  of  temperature  than 
the  curves  of  either  of  the  brick  stacks. 
In  these  tests  the  draft  at  the  base  of 
the  chimney  was  measured  and  com- 
pared with  the  calculated  draft,  and 
the  greatest  variation  found  was  0.09 


in. 


440         480 
Temperatures  in  Degrees  Fahr. 


Peabody  and  Miller  give  the  follow- 
ing formula  for  curve  C :  HT"1  =  Kf 
in  which  //  is  any  height  above  the 
middle  of  the  flue ;  T  =  temperature 
°F.  +  460;  log  K  ==  75.4  and  n  =  25. 
It  is  evident  that  this  formula  applies 

~       only  to  the  particular  conditions  under 
FIG.  278.— TEMPERATURES  AT  DIF-     ,.,,,. 
FERENT  HEIGHTS  OF  CHIMNEY.      which    the    chimney    was    tested, "  for 

curve  D,  for  the  same  chimney,  gives 
approximately  log  K  =  143  and  n  =  48.7. 

The  average  temperature  in  the  250-ft.  chimney  according  to  the 
curve  C  is  about  400°,  with  70°  F.  outside  temperature  the  theoretical 
draft,  according  to  the  table  on  page  673  is  1.28  in.  If  the  average 


CHIMNEYS,  677 

• 
temperature  was  the  same  as  the  initial  temperature  the  draft  would 

be  1.48  in. 

High  Chimneys  not  Necessary. — Chimneys  above  150  ft.  in  height 
are  very  costly,  and  their  increased  cost  is  rarely  justified  by  increased 
efficiency.  In  recent  practice  it  has  become  somewhat  common  to 
build  two  or  more  smaller  chimneys  instead  of  one  large  one.  A 
notable  example  is  the  Spreckles  Sugar  Refinery  in  Philadelphia, 
where  three  separate  chimneys  are  used  for  one  boiler-plant  of  7500 
H.P.  The  three  chimneys  are  said  to  have  cost  several  thousand 
dollars  less  than  a  single  chimney  of  their  combined^  capacity  would 
have  cost.  Very  tall  chimneys  have  been  characterized  by  one  writer 
as  "monuments  to  the  folly  of  their  builders." 

Size  of  Chimneys  corresponding  to  Given  Capacity  of  Boilers, — 

The  formula  given  below,  and  the  table  calculated  therefrom  for 
chimneys  up  to  96  ins.  diameter  and  200  ft.  high  were  first  published 
by  the  author  in  1884  (Trans.  A.  S.  M.  E.,  vi.  81).  They  have  met 
with  much  approval  since  that  date  by  engineers  who  have  used 
them,  and  have  been  frequently  published  in  boiler-makers'  catalogues 
and  elsewhere.  The  table  is  now  extended  to  cover  chimneys  up  to 
12  ft.  diameter  and  300  ft.  high.  The  sizes  corresponding  to  the 
given  commercial  horse-powers  are  believed  to  be  ample  for  all  cases 
in  which  the  draft  areas  through  the  boiler-flues  and  connections  are 
sufficient,  say  not  less  than  20  per  cent  greater  than  the  area  of  the 
chimney,  and  in  which  the  draft  between  the  boilers  and  chimney  is 
not  checked  by  long  horizontal  passages  and  right-angled  bends. 

Note  that  the. figures  in  the  table  correspond  to  a  coal  consumption 
of  5  Ibs.  of  coal  per  horse-power  per  hour.  This  liberal  allowance  is 
made  to  cover  the  contingencies  of  poor  coal  being  used,  and  of  the 
boilers  being  driven  beyond  their  rated  capacity.  In  large  plants 
with  economical  boilers  and  engines.,  good  fuel  and  other  favorable 
conditions,  which  will  reduce  the  maximum  rate  of  coal  consumption 
at  any  one  time  to  less  than  5  Ibs.  per  H.P.  per  hour,  the  figures  in  the 
table  may  be  multiplied  by  the  ratio  of  5  to  the  maximum  expected  coal 
consumption  per  H.P.  per  hour.  Thus,  with  conditions  which  make 
the  maximum  coal  consumption  only  2.5  Ibs.  per  hour,  the  chimney 
300  ft.  high  X  12  ft.  diameter  should  be  sufficient  for  6155  X  2  = 
12,310  horse-power.  The  formula  is  based  on  the  following  data: 

1.  The  draft-power  of  the  chimney  varies  as  the  square  root  of  the 
height. 

2.  The  retarding  of  the  ascending  gases  by  friction  may  be  con- 
sidered as  equivalent  to  a  diminution  of  the  area  of  the  chimney,  or 
to  a  lining  of  the  chimney  by  a  layer  of  gas  which  has  no  velocity. 
The  thickness  of  this  lining  is  assumed  to  be  2  ins.  for  all  chimneys, 
or  the  diminution  of  area  equal  to  the  perimeter  X  2  ins.  (neglecting 
the  overlapping  of  the  corners  of  the  lining) .     Let  D  =  diameter  in 
feet,  A  =  area,  and  E  =  effective  area  in  square  feet. 


678  STEAM-BOILER  ECONOMY. 

87)  9 

For  square  chimneys,  E  =  D2  —  —  =  A  —  - 

\.£t  O 

For  round  chimneys,  E  =  j(-D2  "To")  =  A  —  0.591  \/A. 

For  simplifying  calculations,  the  coefficient  of  \/A  may  be  taken 
as  0.6  for  both  square  and  round  chimneys,  and  the  formula  becomes 

E  =  A  -  0.6VX 

3.  The  power  varies  directly  as  this  effective  area  E. 

4.  A  chimney  should  be  proportioned  so  as  to  be  capable  of  giving 
sufficient  draft  to  cause  the  boiler  to  develop  much  more  than  its 
rated  power,  in  case  of  emergencies,  or  to  cause  the  combustion  of 
5  Ibs.  of  fuel  per  rated  horse-power  of  boiler  per  hour. 

5.  The  power  of  the  chimney  varying  directly  as  the  effective  area, 
E,  and  as  the  square  root  of  the  height,  //,  the  formula  for  horse- 
power of  boiler  for  a  given  size  of  chimney  will  take  the  form  H.P. 
=  CE\/H,   in  which  C  is  a  constant,   the  average  value  of  which, 
obtained  by  plotting  the  results  obtained  from  numerous  examples 
in  practice,  the  author  finds  to  be  3.33. 

The  formula  for  horse-power  then  is 

H.P.  =  3.33#V#,     or     H.P.  =  3.33(A  -  0.6VT)V77. 


Pounds  of  coal  per  hour  =  16.65  (A—  0.6 
If  the  horse-power  of  boiler  is  given,  to  find  the  size  of  chimney, 
the  height  being  assumed, 


For  round  chimneys,  diameter  of  chimney  =  diam.  of  E  -f  4  ins. 

For  square  chimneys,  side  of  chimney  =  VE  -f  4  ins. 

If  effective  area  E  is  taken  in  square  feet,  the  diameter  in  inches 
is  d  =  13. 5±VE  +4  ins.,  and  the  side  of  a  square  chimney  in  inches 
is  s  =  l%vE  +  4  ins. 

If  horse-power  is  given  and  area  assumed,  the  height  H  = 
0.3  H.PA2 


In  proportioning  chimneys  the  height  is  generally  first  assumed, 
with  due  consideration  to  the  heights  of  surrounding  buildings  or 
hills  near  to  the  proposed  chimney,  the  length  of  horizontal  flues,  the 
character  of  coal  to  be  used,  etc.,  and  then  the  diameter  required  for 


CHIMNEYS. 


679 


lipS? 

gfjafl* 

H     U         V 


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|2 

II 


680  STEAM-BOILER  ECONOMY. 

the  assumed  height  and  horse-power  is  calculated  by  the  formula  or 
taken  from  the  table  on  page  679. 

Velocity  of  Gas  in  Chimneys. — The  velocity  of  the  heated  gas, 
based  on  the  chimney  proportions  given  in  the  table,  may  be  found 
from  the  following  data: 

A  =  Lbs.  coal  per  hour  =  boiler  horsepower  X  5 ; 
B  =  Lbs.  gas  per  Ib.  coal  =  say  20  Ibs. ; 
C  =  Cu.  ft.  of  gas  per  Ib.  of  gas 

=  12.4  X  (temp,  of  gas  +  460)  -~  492  ; 

=  25  cu.  ft.  for  532°  F.  =  500  cu.  ft.  per  Ib.  coal; 
V  =  Velocity   of   gas,    feet    per    second  =  AX^XCr-^-( Chimney 
area,  sq.  ft,  X  3600). 

Based  on  a  gas  temperature  of  532°  F.,  5  Ibs.  coal  per  hour  per 
rated  H.P.,  and  20  Ibs.  gas  per  Ib.  of  coal  we  have 

Cu.  ft.  gas  per  second  per  Ib.  of  coal  per  hour  =  0.1389 ; 
"          "  "          "     boiler    horsepower    =0.6944; 

and  the  velocities  in  feet  per  second,  based  on  the  effective  areas 
given  in  the  table,  corresponding  to  different  heights  of  chimney  are : 

Height,  feet....  50   60   70   80   90   100  110  125  150  175  200  225  250  300 
Veloc.,ft.persec.  16.3  17.8  19.4  20.7  22.0  23.2  24.3  25.9  28.3  30.6  32.7  34.7  36.6  40.1 

Chimneys  with  Forced  Draft. — When  natural,  or  chimney,  draft 
only  is  used,  the  function  of  the  chimney  is  1,  to  produce  such  a  dif- 
ference of  pressure,  or  intensity  of  draft,  between  the  bottom  of  the 
chimney  and  the  ash  pit  as  will  cause  the  flow  of  the  required 
quantity  of  air  through  the  grate  bars  and  the  fuel  bed,  and  the  flow 
of  the  gases  of  combustion  through  the  gas  passages,  the  damper 
and  the  breeching;  and  2,  to  convey  the  gases  above  the  tops  of  sur- 
rounding buildings  and  to  such  a  height  that, they  will  not  become  a 
nuisance.  With  forced  draft  the  fan  or  blower  performs  the  function 
of  producing  the  difference  of  pressure,  and  the  only  use  of  the 
chimney  is  that  of  conveying  the  gases  to  a  place  where  they  will 
cause  no  inconvenience;  and  in  that  case  the  height  of  the  chimney 
may  be  much  less  than  that  of  a  chimney  for  natural  draft. 

With  oil  or  natural  gas  for  fuel^  the  resistance  of  the  grates 
and  of  the  fuel  bed  is  eliminated,,  and  the  height  of  the  chimney  may 
be  much  less  than  that  of  one  desired  for  coal  firing.  When  oil  or 
gas  is  substituted  for  coal,  and  the  chimney  is  a  high  one,  it  may  be 
necessary 'to  restrict  its  draft  power  by  a  damper  or  other  means, 


CHIMNEYS.  681 

in  order  to  prevent  its  creating  too  great  a  negative  pressure  in  the 
furnace  and  thereby  too  great  an  admission  of  air,  which  will  cause 
a  decrease  in  efficiency. 

Chimneys  for  Mechanical  Stoker  Installations  with  Forced  Draft. 
— The  manufacturers  of  the  Taylor  stoker  publish  a  series  of  curves 
showing  the  relative  heights,  diameters  and  costs  of  chimneys  for 
Taylor  and  for  natural  draft  furnaces,  from  which  the  figures  in  the 
table  on  the  next  page  are  taken.  A  column  has  been  added  showing 
the  number  of  pounds  of  coal  burned  per  hour  corresponding  with  the 
given  sizes  of  natural  draft  chimneys,  according  to  the  author's 
formula,  Ibs.  coal  per  hour  =  16.65(^4  —  0.6\/^)VH;  which  gives 
about  17%  greater  consumption  with  the  smallest  chimney  and  nearly 
30  per  cent  greater  with  the  largest  than  is  given  by  the  formula 
from  which  the  curve  for  natural  draft  chimneys  was  derived.  This 
formula  is  Ibs.  coal  per  hoi^r  =1%A\/H.  As  the  author's  formula 
and  chimney  table  in  the  more  than  thirty  years  in  which  they  have 
been  extensively  used  have  never  been  shown  to  provide  insufficient 
area  of  chimney  for  a  given  coal  consumption,  but  on  the  contrary 
have  often  been  criticised  as  underestimating  the  quantity  of  coal 
that  can  be  burned  with  a  given  chimney,  this  Taylor  formula  for 
natural  draft  must  give  figures  of  coal  consumption  that  are  far 
too  low.  The  formula  given  for  the  Taylor  stoker  is  Ibs.  coal  per 
hour  =  2i.8J.\/#.  A  —  area  of  chimney  in  sq.  ft.,  H  =  height  in  ft. 
It  is  not  stated  how  the  coefficient  21.8  is  derived.  A  uniform  height 
of  100  ft.  is  given  for  chimneys  with  Taylor  stokers.  This  is  of 
course  ample  with  forced  draft,  and  50  ft.  would  usually  be  sufficient, 
provided  enough  pressure  of  blast  is  provided  beneath  the  stoker  to 
overcome  the  resistance  of  the  tuyeres  and  of  the  fuel  bed,  were  it  not 
that  a  taller  chimney  is  needed  to  carry  the  gases  of  combustion  far 
above  the  roofs  of  neighboring  buildings. 

Chimney  Table  for  Oil  Fuel,  (C.  R.  Weymouth,  Journal  A.  S. 
M.  E.,  Oct.,  1912) — Conditions:  Sea  level;  atmospheric  temperature, 
80°  F. ;  draft  at  chimney  side  of  damper,  0.30  in.;  excess  air,  less 
than  50%,  assumed  50%  for  calculations  of  efficiency  and  chimney 
dimensions;  temperature  of  gases  leaving  chimney,  500°  F. ;  boiler 
efficiency,  73%;  actual  boiler  horse-power,  150  per  cent  of  rated; 
Ibs.  gas  per  actual  boiler  H.P.,  54.6;  height  of  chimney  above  point 
of  draft  measurement,  12  ft.  less  than  tabulated  height.  When 
building  conditions  permit  select  chimneys  of  least  height  in  table 
for  minimum  cost  of  chimney.  Chimney  capacities  stated  are  maxi- 
mum, for  continuous  load  equally  divided  on  all  boilers.  For  large 


682  STEAM-BOILER  ECONOMY. 

SIZES    OF   CHIMNEYS    FOR   NATURAL   DRAFT   AND    FOR   TAYLOR    STOKERS. 


Pounds 
Coal  burned 

Natural  Draft. 

Taylor 
Stoker. 

Cost  of  Chimney. 

Pounds 
Coal  per 

TT  *•      \*  o  +  1  1  »»  o  1 

per  Hr. 
Taylor 
Formula. 

Height  of 
Chimney. 
Ft. 

Diam.  of 
Chimney. 
Ins. 

Chimney 
Diam.* 
Ins. 

Natural 
Draft. 

Taylor 
Stoker. 

lir.    IN  fitUTEl 

Draft. 
Kent 
Formula.  f 

2,000 

93 

56 

41 

$2,600 

$2,000 

2,350 

4,000 

124 

74 

58 

4,600 

2,900 

4,930 

6,000 

145 

87 

70 

6,300 

3,500 

7,500 

8,000 

162 

98 

82 

7,900 

4,100 

10,180 

10,000 

177 

107 

92 

9,500 

4,600 

12,780 

12,000 

190 

116 

101 

11,000 

5,000 

15,380 

14,000 

204 

124 

109 

12,500 

5,400 

18,630 

16,000 

215 

130 

117 

14,000 

5,800 

21,100 

18,000 

226 

136 

124 

15,500 

6,200 

23,750 

20,000 

235 

142 

131 

16,700 

6,600 

26,470 

22,000 

244 

'  148 

137 

18.000 

6,900 

31,080 

24,000 

252 

153 

143 

19,300 

7,200 

33,750 

26,000 

261 

157 

149 

20,600 

7,500 

34,750 

28,000 

269 

162 

154 

21,800 

7,800 

37,100 

30,000 

276 

166 

159 

23,000 

8,000 

39,530 

32,000 

284 

170 

164 

24,200 

8,200 

42,090 

34,000 

291 

174 

169 

25,400 

8,400 

44,700 

*  All  chimneys,  100  ft.  high.              t  Heights  and  diameters  as  in  2d  and  3d  columns. 
CHIMNEY    TABLE    FOR    OIL    FUEL. (C.    R.  WeymOUth.) 


Height  in  Feet  above  Boiler  Room  Floor. 

Diam. 
In. 

Area. 
Sq.ft. 

80 

90 

100 

110 

120 

130 

140 

150 

160 

Actual  Horse-power  =  150  Per  cent  of  Rated. 

18 

1.77 

63 

75 

84 

91 

96 

101 

104 

108 

110 

24 

3.14 

123 

148 

166 

180 

191 

201 

208 

215 

221 

30 

4.91 

206 

249 

280 

304 

324 

340 

354 

366 

377 

36 

7.07 

312 

379 

427 

466 

497 

523 

545 

564 

581 

42 

9.62 

443 

539 

609 

665 

711 

749 

782 

810 

830 

48 

12.57 

599 

729 

827 

904 

967 

1,020 

1,070 

1,110 

1,145 

54 

15.90 

779 

951 

1,080 

1,180 

1,270 

1,340 

1,400 

1,460 

1,500 

60 

19.64 

985 

1,200 

1,370 

1,500 

1,610 

1,710 

1,790 

1,860 

1,920 

66 

23.76 

1220 

1,490 

1,700 

1,860 

2,000 

2,120 

2,220 

2,310 

2,390 

72 

28.27 

1,470 

1,810 

2,060 

2,260 

2,430 

2,580 

2,710 

2,820 

2,910 

78 

33.18 

1,750 

2,150 

2,460 

2,710 

2,910 

3,000 

3,250 

3,380 

3,500 

84 

38.49 

2,060 

2,530 

2,900 

3,190 

3,440 

3,650 

3,840 

4,000 

4,150 

96 

50.27 

2,750 

3,390 

3,880 

4,290 

4,630 

4,920 

5,180 

5,400 

5,610 

108 

63.62 

3,550 

4,380 

5,020 

5,550 

6,000 

6,390 

6,730 

7,030 

7,300 

120 

78.54 

4,440 

5,490 

6,310 

6,990 

7,560 

8,060 

8,490 

8,890 

9,240 

132 

95.03 

5,450 

6,740 

7,760 

8,600 

9,310 

9,930 

10,500 

11,000 

11,400 

144 

113.1 

6,550 

8,120 

9,350 

10,400 

11,200 

12,000 

12,700 

13,300 

13,800 

156 

132.7 

7,760 

9,630 

11,100 

12,300 

13,400 

14,300 

15,100 

15,800 

16,500 

168 

153.9 

9,060 

11,300 

13,000 

14,400 

15,700 

16,800 

17,700 

18,600 

19,400 

180 

176.7 

10,500 

13,000 

15,100 

16,700 

18,200 

19,500 

20,600 

21,600 

22,600 

CHIMNEYS.  683 

plants  or  swinging  load,  reduce  capacity  10  to  20%.  Breeching 
20%  in  excess  of  stack  area  length  not  exceeding  10  chimney  diam- 
eters. See  second  table  on  page  682.) 

In  using  the  above  table  it  must  be  noted  that  the  conditions 
upon  which  it  is  based  are  all  fairly  good.  With  unskillful  handling 
of  oil  fuel  the  excess  air  is  apt  to  be  much  more  than  50%  and  the 
efficiency  much  less  than  73%.  In  that  case  the  actual  horse-power 
developed  by  a  given  size  of  chimney  may  be  much  less  than  the 
figure  given  in  the  table. 

DRAFT   OF    CHIMNEYS    100    FT.    HIGH — OIL   FUEL 

Temp,    of    gases    entering 

chimney 300        400        500        600        700 

Net  chimney  draft,  inches  of  water 
f   60°  F.    0.367    0.460    0.534    0.593    0.642 

Temp,  of  outside  air {    80          0.325    0.417    0.490    0.550    0.599 

[100          0.284    0.377    0.451    0.510    0.559 

The  net  draft  is  the  theoretical  draft  due  to  the  difference  in 
weight  of  atmospheric  air  and  chimney  gases  at  the  stated  temperatures, 
multiplied  by  a  coefficient,  0.95,  for  temperature  drop  in  stack,  and 
by  5/6  as  a  correction  for  friction.  For  high  altitudes  the  draft 
varies  directly  as  the  normal  barometer.  For  other  heights  than 
100  feet  (measured  above  the  level  of  entrance  of  the  gases)  the 
draft  varies  as  the  square  root  of  the  height. 

Regulation  of  Draft  with  Variable  Loads  and  Oil  Firing.  (E. 
W.  Kerr,  Bulletin  131  Louisiana  State  University.  Experiments  with 
Oil  Burning  in  Boiler  Furnaces). — A  stack  sufficient  to  give  the  draft 
required  for  the  maximum  overload  should  be  supplied.  More  than 
this  should  not  be  supplied,  as  it  adds  to  the  danger  of  loss  from  excess 
air  by  careless  firemen.  In  one  test,  with  a  small  load  (75%)  and 
the  damper  wide  open,  the  lowest  efficiency  was  obtained,  the  equivalent 
evaporation  being  13.2  Ibs.  of  water  per  Ib.  of  oil,  as  compared  with 
15.8  Ibs.  with  the  best  possible  regulation.  This  test  was  made 
with  the  openings  into  the  furnace  carefully  regulated.  With  a  wide 
open  draft  door  the  loss  might  be  much  greater.  With  the  considerable 
losses  in  efficiency  due  to  excessive  draft  shown  by  these  tests,  it  is 
clear  that  flue  dampers  are  essential  for  the  best  results.  Of  course, 
the  chimney  can  be  proportioned  so  as  to  give  the  proper  draft  for 
the  maximum  load  to  be  carried,  though  for  rated  and  under-loads 
a  chimney  thus  proportioned  would  give  a  draft  too  strong  for  the 
best  economy  and  the  only  possible  remedy  is  to  use  a  flue  damper. 
Since  the  best  boiler  efficiency  is  not  only  dependent  upon  the  proper 
air  supply  but  upon  proper  and  regular  loading,  it  is  best,  as  far  as  pos- 
sible, to  take  care  of  the  variations  in  loads  with  as  few  boilers  as  possi- 
ble. In  other  words,  instead  of  reducing  slightly  the  fuel  supply  to  all 
.of  the  oil  burners  when  the  load  is  reduced,  it  is  better  to  make  the  re- 
duction with  one  or  two  boilers  and  never  change  the  others.  Such  an 


684  STEAM-BOILER  ECONOMY. 

arrangement  makes  it  possible  to  operate  the  constantly  loaded  boilers 
under  conditions  known  to  be  best.  In  other  words,  this  does  away 
with  much  uncertainty.  The  dampers  for  these  boilers  can  be  set  at 
the  proper  position,  the  only  damper  manipulation  required  being 
for  the  small  number  of  boilers  used  in  handling  the  variation  in  load. 
Lightning  Conductors  are  usually  attached  to  tall  masonry  chim- 
neys. The  Carl  Bajohr  L.  C.  Co.,  of  St.  Louis,  issues  a  detailed 
specification  for  such  conductors,  which  provides  for  two  conductors 
placed  on  opposite  sides  of  the  chimney,  leading  to  copper  plates 
placed  15  feet  deep  in  moist  earth,  each  conductor  consisting  of  a 
copper  cable  of  315,000  circular  mils  in  cross  section.  Four  points 
of  bronze  with  platinum  covered  tips,  are  carried  by  %  in.  copper 
rods  above  the  chimney.  Special  precautions  for  making  the  joints 
and  installing  the  conductors  are  described. 

Chimneys  for  Dissipating  Smoke. — A  German  invention  for  dis- 
sipating smoke  by  mixing  it 
with  the  air  surrounding  the 
chimney  is  described  in  Power, 
April  2,  1912.  The  upper  part 
of  the  chimney,  one-fourth  to 
one-third  its  height  is  latticed 
by  horizontal  channels,  shown 
in  cross-section  in  Fig.  279. 
Air  enters  through  the  slots  on 
FIG.  279,-DEvicE^FOR  DISSIPATING  the  windward  side  Of  the  chim- 
ney, mixes  with  the  smoke  and 

escapes  on  the  opposite  side,  thus  diluting  the  smoke  into  a  foggy  mist. 
The   Design   of  Breechings   and   Smoke   Flues.     (T.   A.    Marsh, 
Industrial  Engineering,  'Nov.  1912). — Some  of  the  features  to  be  con- 
sidered in  the  design  of  a  breeching  are: 

1.  For  a  given  area  a  circular  flue  is  more  desirable  than  a  rect- 
angular flue,  due  to  the  fact  that  the  draft  loss  therein  due  to  friction 
is  less. 

2.  Sharp  bends  and  angles  should  be  avoided,  as  these  give  rise 
to  draft  losses  of  a  considerable  magnitude. 

3.  Underground    flues    are    undesirable    from    two    standpoints, 
namely,  inaccessibility  for  cleaning,  and  draft  losses  due  to  tempera- 
ture drop  in  those  cases  where  water  can  accumulate  in  the  bottom  of 
such  flues. 

4.  Opposing  currents  of  gases  should  not  be  allowed  to  meet, 
but  a  deflector  should  be  provided  to  direct  the  gas  currents  in  the 
proper  direction. 

5.  The  cross-section  of  a  flue  should  not  be  suddenly  increased  or 
decreased  in  area,  as  the  result  is  a  marked  draft  loss. 

6.  Steel    breechings    are    more    desirable    than    those    of   brick 
or  cement,  due  to  less  draft  loss,  but  for  the  best  results  all  steel 
breechings  should  be  covered  to  prevent  radiation  and  air  infiltration. 

A  common  design  of  breeching  is  shown  in  No.  1.    This  represents 


CHIMNEYS. 


685 


a  length  of  breeching  into  which  the  uptakes  of  several  boilers 
discharge.  The  connections  are  usually  made  without  any  provision 
for  the  entrance  of  the  gases  into  the  main  breeching  other  than  at 
right  angles.  The  result  of  this  is  that  the  gases  entering  from  the 
uptake  A  have  a  tendency  to  cut  across  the  main  breeching  be- 
fore their  direction  is  changed.  The  result  of  this  is  a  restriction  of 
the  area  D,  resulting  in  an  eddy  at  this  point  and  a  virtual  reduction 
of  the  breeching  area  from  this  cause.  In  case  breeching  A  is  being 
worked  to  its  full  capacity,  this  reduction  of  effective  area  is  con- 
siderable and  the  draft  loss  at  the  point  B  is  noticeable.  The 


No.  1. 


No.  2. 


No.  3. 


FIG.  280. — DESIGNS  OF  BREECHINGS. 

correction  of  this  difficulty  lies  in  the  design  of  the  breeching  at 
the  point  C  so  that  the  gases  will  enter  the  breeching  B  in  somewhat 
nearly  the  same  direction  of  flow. 

No.  2  is  the  usual  style  of  breeching  used  to  serve  boilers  on  both 
sides  of  a  chimney  with  the  chimney  out  of  line  with  the  breeching. 
The  result  is  the  T-shaped  design  shown.  The  gases  from  the  side  B 
meet  the  gases  from  the  side  A  in  head-on  collision  causing  a  reduction 
in  draft  pressure.  Such  a  design  often  results  in  a  draft  loss  of  0.25  in. 
of  water.  The  correction  for  this  design  is  effected  by  inserting  long 
radius  bends  as  shown  in  dotted  lines  on  the  figure.  A  curved  de- 
flector as  shown  in  dotted  outline  might  also  prove  to  be  beneficial. 

No.  3  represents  the  placing  of  a  baffle  in  the  base  of  a  chimney 
to  prevent  the  gases  from  opposing  breechings  meeting  in  head-on 
collision.  The  preferable  design  of  a  chimney  baffle,  however,  is 


686 


STEAM-BOILER  ECONOMY. 


curved  as  shown  by  the  dotted  line  E-F.  This  construction  results 
in  but  a  slight  draft  loss  at  this  point,  the  gases  being  gradually 
diverted  and  caused  to  turn  upward  in  a  spiral  path. 

Breeching  areas  should  be  designed,  not  as  some  function  of  grate 
surface  served,  but  to  accommodate  a  given  volume  of  gas  at  a  limited 
velocity.  This  volume  of  gas  is  determined  from  the  amount  of  coal 


FIG.  281, — STACK  CONNECTION  FOR  Six  BOILERS. 

to  be  burned  in  order  to  obtain  the  desired  boiler  ratings,  and  from 
the  amount  of  air  used  per  pound  of  coal.  A  safe  rule  for  gas  velocity 
in  breechings  is  to  so  design  that  35  ft.  per  second  shall  be  the 
limiting  figure.  Beyond  this  figure,  draft  losses  due  to  friction  soon 
become  excessive. 

Fig.  281  shows  a  stack  connection  for  six  water-tube  boilers  de- 
signed by  John  L.  Gill,  Jr.,  in  1892.     The  right-hand  boiler  of  each 


FIG.  282. — RADIAL  BRICK  CHIMNEYS.        FIG.  283. — RADIAL  BRICK. 

battery  discharges  its  gas  into  the  lower  one  of  the  two  flues  shown 
below 'the  drum.  By  this  arrangement  the  stream  of  gas  from  any 
one  does  not  tend  to  obstruct  the  stream  from  any  other,  and  the 
draft  is  thus  equalized  for  all  the  boilers. 

Radial  Brick  Chimneys. — Fig.  282  shows  a  portion  of  a  chimney 
built  of  special  shapes  of  brick,  shown  in  Fig.  283.     By  the  use  of 


CHIMNEYS. 


687 


these  brick  chimneys  may  be  built  much  more  cheaply  than  by  the 
use  of  ordinary  rectangular  brick,  and  the  old  style  of  chimney  is 
now  now  longer  in  fashion.  They  have  been  extensively  introduced 
since  about  1900.  A  more  recent  form  of  chimney  is  made  of  re- 
inforced concrete  as  shown  below. 

Specifications  for  Concrete  Chimneys. — Following  are  extracts 
from  the  specifications  of  the  General  Concrete  Construction  Co., 
Chicago.  Fig.  284  gives  an  idea  of  -the  method  of  construction. 


Vertical  Stee 
Horizontal  Steel 
Concrete  Wall 
Air  Space 


Brick  Lining 


Boiler  Room  Floor 


Rectilinear  Net 
^Diagonal  Net 

FIG.  284. — CONSTRUCTION  OF  A  CONCRETE  CHIMNEY.'] 

Reinforcement. — The  foundation  will  be  reinforced  with  two  nets 
of  f-in.  square  twisted  steel;  the  lower  net  placed  diagonally  and 
steel  spaced  12  in.  centers;  the  upper  net  placed  parallel  to  sides, 
steel  spaced  24  in.  centers.  The  vertical  reinforcement  in  the  chim- 
ney will  consist  of  f-in.  square  twisted  steel;  sufficient  bars  will 
be  used  to  absorb  all  tension  without  stressing  it  beyond  16,000  Ibs. 
per  sq.  in.  Eods  will  be  uniformly  spaced,  and  placed  3  ins.  from  the 
outer  surface  of  the  concrete.  Joints  will  lap  30  ins.  The  vertical 
rods  will  be  embedded  in  the  foundation  and  bent  under  foundation 
steel  for  anchorage.  The  horizontal  reinforcement  will  be  a  steel 
net  consisting  of  j-in.  longitudinal  rods  spaced  4  in.  centers,  triangu- 
larly laced,  the  ends  lapping  6  ins.  This  net  will  be  placed  around 
and  wired  at  intervals  to  vertical  steel. 

Concrete. — The  concrete  in  the  foundation  will  be  mixed  in  the 
proportion  of  1  part  Portland  cement,  3  parts  clean  sand  and  6  parts 
crushed  stone  or  gravel.  The  concrete  in  the  chimney  will  be  a  "wet 
mixture"  of  1  part  Portland  cement,  2J  parts  clean  sand  and  3  parts 
of  1-in.  crushed  stone  or  gravel. 


688  STEAM-BOILER  ECONOMY. 

Lining. — The  lining  will  consist  of  a  good  grade  of  hard  burned 
brick,  covered  with  a  concrete  cap,  and  separated  from  the  concrete 
shell  by  an  insulating  air  space. 

Design  and  Guarantee. — The  foundation  will  be  of  such  size  that 
the  resultant  of  forces  will  fall  within  the  middle  third,  and  the  maxi- 
mum compression  from  live  and  dead  load  will  not  exceed  the  safe 
bearing  value  of  the  soil.  The  shell  at  the  base  of  shaft  will  be  of  such 
thickness  that  the  maximum  compression  on  concrete  will  not  ex- 
ceed 350  Ibs.  per  sq.  in.  At  the  smoke  opening  the  thickness  of 
shell  will  be  increased  about  30%  on  each  side  and  extending  5  ft. 
above  and  below,  and  additional  reinforcement  provided.  The  chim- 
ney will  be  designed  to  withstand  a  wind  pressure  due  to  a  wind  hav- 
ing a  velocity  of  100  miles  an  hour  and  chimney  gases  not  exceeding 
1000°  F.  For  a  period  of  five  years  after  completion  we  will  repair 
free  of  charge  any  defects  arising  from  faulty  design,  defective 
materials  or  workmanship. 


CHAPTEE  XIX. 
MISCELLANEOUS. 

ECONOMIZERS. — FLUE-GAS  ANALYSES  AND  THE  HEAT  BALANCE. — Loss  OF  FUEL 
DUE  TO  KEEPING  UP  STEAM- PRESSURE  IN  IDLE  BOILERS. — COAL  USED  IN 
BANKED  FIRES  NOT  A  MEASURE  OF  RADIATION. — COST  OF  COAL  PER  BOILER 
HORSE-POWER  PER  YEAR. — BOILER-ROOM  LABOR. — TASK  SETTING  FOR 
FIREMEN. — STEAM-BOILER  PRACTICE  OF  THE  FUTURE. 

Economizers. — The  Green  Economizer,  Fig.  285,  consists  of  a  rec- 
tangular chamber  of  brick-work  filled  with  a  great  number  of  vertical 
cast-iron  water-tubes.  The  waste  heat  from  the  cylinder  boilers  is 
carried  into  this  chamber  before  being  allowed  to  enter  the  chimney, 
and  heats  the  feed-water,  which  passes  through  the  tubes  under  pres- 
sure, to  a  temperature  approaching  that  of  the  steam  generated  in  the 
boiler.  This  economizer  is  very  commonly  used  in  England  with 
Lancashire  boilers,  and  has  been  largely  introduced  in  this  country, 
especially  in  large  plants  such  as  sugar  refineries.  The  advisability 
of  its  use  in  any  particular  case  is  a  matter  of  close  calculation,  in 
which  the  factors  are  quantity  of  coal  used  and  of  water  evaporated 
by  the  boilers,  temperature  of  the  feed-water,  temperature  of  the  waste 
gases  from  the  boiler,  cost  of  the  economizer,  annual  cost  for  interest 
and  probable  repairs,  and  probable  saving  by  the  economizer. 

Data  for  Proportioning  a  Green  Economizer. — The  Fuel  Econo- 
mizer Co.  makes  the  following  statement  concerning  the  amount  of 
heating  surface  to  be  provided  in  an  economizer  to  be  used  in  connec- 
tion with  the  given  amount  of  boilers,  and  concerning  the  results 
which  may  be  expected  from  the  economizer : 

We  have  found  in  practice  that  by  allowing  4  sq.  ft.  of  heating 
surface  per  boiler  horse-power  (34J  Ibs.  of  water  evaporated  from  and 
at  212°  —  1  H.P.),  we  are  able  to  raise  the  feed-water  60°  for  every 
100°  reduction  in  the  temperature,  entering  the  economizer  with  gases 
from  450°  to  600°. 

With  temperature  entering  the  economizer  at  600°  to  700°  we  have 
allowed  a  heating  surface  of  4-J  to  5  sq.  ft.  of  heating  surface  per 
boiler  horse-power,  and  for  every  100°  reduction  of  gases  we  have 
obtained  about  65°  rise  in  temperature  of  the  water;  the  temperature 
of  the  feed-water  entering  averaging  from  60°  to  120°. 

689 


690 


STEAM-BOILER  ECONOMY. 


MISCELLANEOUS.  691 

With  5000  sq.  ft.  of  boiler  heating  surface  (plain  cylinder  boilers) 
developing  1000  H.P.,  we  should  recommend  using  5  sq.  ft.  of  econo- 
mizer heating  surface  per  boiler  H.P.,  or  an  economizer  of  about  500 
tubes,  and  it  should  heat  the  feed- water  about  300°. 

Calculation  of  the  Saving  Effected  by  an  Economizer. — If  there 
were  no  loss  by  radiation  from  the  economizer,  and  no  leakage  of  air 
into  its  brick  setting,  the  heat  loss  by  the  gases  in  passing  through  it, 
as  measured  by  their  difference  in  temperature  on  entering  and  leaving, 
would  exactly  equal  the  heat  added  to  the  feed-water.  The  usual 
method  of  calculating  the  saving  of  fuel  by  an  economizer  when  the 
boiler  and  the  economizer  are  tested  together  as  a  unit  is  by  the 
formula  (H^  —  h)  -r-  (II 2  —  /i),  in  which  h  is  the  total  heat  above 
32°  of  1  Ib.  of  water  entering,  77  ±  the  total  heat  of  1  lb.  of  water 
leaving  the  economizer,  and  772  the  total  heat  above  32°  of  1  lb.  of 
steam  at  the  boiler  pressure.  If  h  =  100,  H^  =  210,  H2  =  1200, 
then  the  saving  according  to  the  formula  is  (210  --  100)  -f-  1100 
=  10%.  This  is  correct  if  the  saving  is  defined  as  the  ratio  of 
the  heat  absorbed  by  the  economizer  to  the  total  heat  absorbed  by 
the  boiler  and  economizer  together,  but  it  is  not  correct  if  the  saving 
is  defined  as  the  saving  of  fuel  made  by  running  the  combined  unit 
as  compared  with  running  the  boiler  alone  making  the  same  quantity 
of  steam  from  feed-water  at  the  low  temperature,  so  as  to  cause  the 
boiler  to  furnish  772  —  h  heat  units  per  lb.  instead  of  H2  —  77^  In 
this  case  the  boiler  is  called  on  to  do  more  work,  and  in  doing  it  may 
be  overdriven  and  work  with  lower  efficiency. 

In  a  test  made  by  F.  G.  Gasche,  in  Kansas  City  in  1897,  using 
Missouri  coal  analyzing  moisture  7.58;  volatile  matter,  36.69;  fixed 
carbon,  35.02;  ash,  15.69;  sulphur  5.12,  he  obtained  an  evaporation 
of  5.17  Ibs.  from  and  at  212°  per  lb.  of  coal  with  the  boiler  alone, 
and  when  the  boiler  and  economizer  were  tested  together  the  equiv- 
alent evaporation  credited  to  the  boiler  was  5.55,  to  the  economizer 
0.72,  and  to  the  combined  unit  6.27,  the  saving  by  the  combined  unit 
as  compared  with  the  boiler  alone  being  (6.27  —  5.17)  -~-  6.27  = 
17.5%,  while  the  saving  of  heat  shown  by  the  economizer  in  the  com- 
bined test  is  only  (6.27  —  5.55)  -f-  6.27  =11.5%. 

The  maximum  saving  of  fuel  which  may  be  made  by  the  use 
of  an  economizer  when  attached  to  boilers  that  are  working  with 
reasonable  economy  is  about  15%.  Take  the  case  of  a  condensing 
engine  using  steam  of  125  Ibs.  gauge  pressure,  and  with  a  hot-well 
or  feed-water  temperature  of  100°  F.  The  economizer  may  be 


692  STEAM-BOILER  ECONOMY. 

expected  under  the  best  conditions  to  raise  this  temperature  about 
170°,  or  to  270°.  Then  h  =  68,  H1  =  239,  H2  =  1190.  (H^ 
-  h)  -r-  (H2  —  h)  =  171  -T-  1122  =  15.24%. 

If  the  boilers  are  not  working  with  fair  economy  on  account 
of  being  overdriven,  then  the  saving  made  by  the  addition  of  an 
economizer  may  be  much  greater. 

The  amount  of  saving  of  fuel  that  may  be  made  by  an  economizer 
varies  greatly  according  to  the  conditions  of  operation.  With  a  given 
quantity  of  chimney  gases  to  be  passed  through  it,  its  economy  will 
be  greater  (1)  the  higher  the  temperature  of  these  gases;  (2)  the 
lower  the  temperature  of  the  water  fed  into  it;  and  (3)  the  greater 
the  amount  of  its  heating  surface.  From  (1)  it  is  seen  that  an 
economizer  will  save  more  fuel  if  added  to  a  boiler  that  is  overdriven 
than  if  added  to  one  driven  at  a  nominal  rate.  From  (2)  it  appears 
that  less  saving  can  be  expected  from  an  economizer  in  a  power 
plant  in  which  the  feed-water  is  heated  by  exhaust  steam  from  auxil- 
iary engines  than  when  the  feed-water  entering  it  is  taken  directly 
from  the  condenser  hot-well.  The  amount  of  heating  surface-  that 
should  be  used  in  any  given  case  depends  not  only  on  the  saving  of 
fuel  that  may  be  made,  but  also  on  the  cost  of  coal,  and  on  the  an- 
nual costs  of  maintenance,  including  interest,  depreciation,  etc. 

The  following  table  shows  the  theoretical  results  possibly  attain- 
able from  economizers  under  the  conditions  specified.  It  is  assumed 
that  the  coal  has  a  heating  value  of  15,000  B.  T.  U.  per  Ib.  of  com- 
bustible; that  it  is  completely  burned  in  the  furnace  at  a  temperature 
of  2500°  F. ;  that  the  boiler  gives  efficiencies  ranging  from  60  to  75 
per  cent  according  to  the  rate  of  driving;  and  that  sufficient  econo- 
mizer surface  is  provided  to  reduce  the  temperature  of  the  gases  in 
all  cases  to  300°  F.  Assuming  the  specific  heat  of  the  gases  to  be 
constant,  and  neglecting  the  ioss  of  heat  by  radiation,  the  temperature 
of  the  gases  leaving  the  boiler  and  entering  the  economizer  is  directly 
proportional  to  (100  -  -  %  of  boiler  efficiency),  and  the  combined 
efficiency  of  boiler  and  economizer  is  (2500  --  300)  -f-  2500  =  88 
per  cent,  which  corresponds  to  an  evaporation  of  (15,000  H-  970)  X 
0.88  =  13.608  Ibs.  from  and  at  212°  per  Ib.  of  combustible;  or  assum- 
ing the  feed-water  enters  the  economizer  at  100°  F.  and  the  boiler 
makes  steam  of  150  Ibs.  absolute  pressure,  to  an  evaporation  of  11,729 
Ibs.  under  these  conditions.  Dividing  this  figure  into  the  number 
of  heat  units  utilized  by  the  economizer  per  pound  of  combustible 
gives  the  heat  units  added  to  the  water,  from  which,  by  reference  to  a 


MISCELLANEOUS. 


693 


steam  table,  the  temperature  may  be  found, 
obtain  the  results  given  in  the  table  below : 


With'  these  data  we 


Boiler  Efficiency,  Per  Cent. 

60 

65 

70 

75 

B.T.U.  absorbed  by  boiler  per  Ib.  combustible. 
B.T.U.  in  chimney  gases  leaving  boiler  .  . 

9000 
6000 

9750 
5250 

10500 
4500 

11250 
3750 

Estimated  temp,  of  gases  leaving  boiler  
Estimated  temp,  of  gases  leaving  economizer  .  . 
B.T.U.  saved  by  economizer 

1000° 
300° 
4200 

875° 
300° 
3450 

750° 
300° 
2700 

625° 
300° 
1950 

Efficiency  gained  by  economizer,  %  
Equivalent  water  evap.  per  Ib.  comb,  in  boiler. 
B.T.U.  saved  by  econ.  equivalent  to  evap.  of  Ibs. 
Temp,  of  water  leaving  economizer  

28 
9.278 
4.330 

448° 

23 
10.051 
3.557 

389° 

18 
10.824 
2.884 
327° 

13 

11.598 
2.010 
265° 

Efficiency  of  economizer  % 

70 

65  7 

60 

52 

Equation  of  the  Economizer.  —  Let  W  =  Ibs.  of  water  evaporated 
by  the  boiler,  under  actual  condition  of  feed-water  temperature  and 
steam  pressure,  per  Ib.  of  combustible  ;  G  =  Ibs.  of  flue-gas  per  Ib. 
combustible  ;  T^  and  T2  =  temperatures  of  gas  entering  and  leaving 
the  economizer  ;  t^  and  t2  =  temperatures  of  water  entering  and 
leaving  the  economizer;  then  assuming  no  loss  by  radiation  and 
leakage,  and  taking  the  specific  heat  of  the  gas  at  0.24  and  that 
of  the  water  at  1, 


-  T2)  = 


-  Tt), 


in  which  F  has  the  values  in  the  following  table  for  given  values 
of  W  and  G. 


w= 

8 

9 

10 

11 

12 

F=^G/W. 

0.54 

0.48 

0.43 

0.39 

0.36 

21 

0.63 

0.56 

0.50 

0.46 

0.42 

24 

0.72 

0.64 

0.58 

0.52 

0.48 

27 

0.81 

0.72 

0.65 

0.59 

0.54 

30 

0.90 

0.80 

0.72 

0.65 

0.60 

Tx  is  usually  fixed  by  the  operating  conditions  of  the  boiler, 
and  tt  by  the  condenser  and  feed-water  heater  conditions. 

Taking  2\  at  800,  700  and  600°,  corresponding  values  of  F  at 
0.43,  0.39  and  0.36,  and  ^  =  100°, 


694  STEAM-BOILER  ECONOMY. 

ti  -100  =  0.43 (800  -T8);    let  712  =  30C,  then  (2=0.43(500) +100  =  3 15°. 
0.39(70C-T2);  250,  0.39  (450) +  100  =  266°. 

0136  (600 -!F2);  220,  0.36  (380) +100  =  237°. 

The  mean  temperature  difference  between  the  flue  gas  and  the 
water, 

=  TI  +  T2  _  t2  +ti     TI  - 12  +  y2  -  h 

22  2 

For  the  three  cases  given  tm  =  343°,  292°,  242°. 

If  w  =  Ibs.  of  water  heated  by  the  economizer  per  hour  from 
t^  to  t2,  8  =  sq.  ft.  of  economizer  surface,  and  C  —  heat  units 
transmitted  per  square  foot  of  surface  per  hour  per  degree  of  mean 
temperature  difference,  then  w(tz  —  tfj  =  SCtm.  The  .value  of  C 
is  given  by  manufacturers  as  ranging  between  2  and  4  for  different 
conditions  of  practice.  It  probably  increases  in  some  proportion  to 
the  increase  of  tm,  but  no  records  of  experiments  have  been  published 
from  which  the  law  of  this  increase  may  be  determined. 

Heat  Transmission  in  Economizers.  Carl  S.  Dow,  Indust.  Eng'g, 
April,  1909.) — The  rate  of  heat  transmission  (C)  per  sq.  ft.  per  hour 
per  degree  of  difference  between  the  average  temperatures  of  the  gases 
and  the  water  passing  through  the  economizer  varies  with  the  mean 
temperature  of  the  gas  about  as  follows:  Gas,  600°,  C  —  3.25;  gas 
500°,  C  =  3;  gas  400°,  C  =  2.75;  gas  300°,  C  =  2.25. 

Test  of  a  Large  Economizer.  (R.  D.  Tomlinson,  Power,  Feb., 
1904.) — Two  tests  were  made  of  one  of  the  sixteen  Green  econ- 
omizers at  the  74th  St.  Station  of  the  Rapid  Transit  Railway,  New 
York  City.  Four  520-H.P.  B.  &  W.  boilers  were  connected  to 
the  economizer.  It  had  512  tubes,  10  ft.  long,  4  9-16  in.  external 
diam. ;  total  heating  surface  6760  sq.  ft.,  or  3.25  sq.  ft.  per  rated 
H.P.  of  the  boilers.  Draft  area  through  econ.  3  sq.  in.  per  H.P. 
The  stack  for  each  16  boilers  and  four  economizers  was  280  ft. 
high,  17  ft.  internal  diam.  The  first  test  was  made  with  the  boilers 
driven  at  94%  of  rating,  the  second  at  113%.  The  results  are  given 
below,  the  figures  of  the  second  test  being  in  parentheses. 

Water  entering  econ.  96°  (93.5°)  ;  leaving  200°  (203.8°)  ;  rise  104 
(110.3). 

Gases  entering  econ.  548°  (603°);  leaving  295  (325);  drop  253 
(278). 

Steam,  gage  pressure,  166  (165).  Total  B.  T.  U.  per  Ib.  from 
feed  temp.  1132  (1134). 


MISCELLANEOUS. 


695 


Saving  of  heat  by  economizer,  per  cent,  9.17  (9.73). 

Reduction  of  draft  in  passing  through  econ.,  in.  of  water,  0.16 
(0.23). 

Results  from  Seven  Tests  of  Sturtevant  Economizers  (Catalogue 
of  B.  F.  Sturtevant  Co.) 


Plants 
Tested. 

Gases 
Entering. 
Deg.  F. 

Gases 
Leaving. 
Deg.  F. 

Water 
Entering. 
Deg.  F. 

Water 
Leaving. 
Deg.  F. 

Increase  in 
Temperature. 

1 

650 

275 

180 

340 

160 

2 

575 

290 

160 

320 

160 

3 

470 

230 

130 

260 

130 

4 

500 

240 

110 

230 

120 

5 

460 

200 

90 

230 

140 

6 

440 

220 

120 

236 

116 

7 

525 

225 

180 

320 

140 

When  to  Install  a  Fuel  Economizer.  (E.  Brown,  Power,  Dec. 
17,  1912).— Assuming  a  1000-H.P.  boiler  plant,  150-lb.  steam  pres- 
sure, temperature  of  escaping  gases  600°  F.,  feed  water  entering  the 
economizer  150°,  increase  of  temperature  by  "passing  through  the 
economizer  100°,  the  calculated  saving  of  fuel  by  using  the  economizer 
is  9.35%.  Taking  4  Ibs.  of  coal  per  boiler  horse-power  per  hour  and 
7200  hours  running  time  per  year,  the  saving  of  coal  figures  up  to 
1350  tons  per  year;  this  multiplied  by  the  cost  of  coal  per  ton 
gives  the  gross  annual  saving  in  dollars. 

From  this  saving  must  be  deducted  all  charges  incident  to  the 
operation  of  the  economizer  as  well  as  interest  on  the  investment. 
Under  ordinary  conditions  a  good  economizer  can  be  installed  for 
about  $6.50  per  horse-power.  This  figure  includes  the  apparatus  itself, 
foundations,  piping,  flues  and  the  increased  height  of  stack  necessary, 
or  an  induced  draft  system. 

These  charges  may  be  tabulated  as  follows: 

Interest  on  investment 5  per  cent 

Depreciation  (assuming  life  of  apparatus  to  be  20 

years) 5  per  cent 

Repairs  and  maintenance 2  per  cent 

Attendance 2  per  cent 

Power  for  operating  scrapers  and  increased  pump- 
ing head  due  to  economizer 3  per  cent 

Miscellaneous 2  per  cent 

Total 19  per  cent 

On  an  investment,  therefore,  of  $6500,  the  estimated  cost  of 
1000-H.P.  of  economizer,  the  total  charges  would  be  $1235,  which 
must  be  deducted  from  the  gross  saving  of  1350  tons  of  coal.  Assuming 
that  coal  can  be  obtained  for  $1  per  ton,  the  gross  saving  would  be 


696  STEAM-BOILER  ECONOMY 

$1350  from  which  must  be  deducted  $1235,  thus  leaving  a  net 
saving  of  $115,  which  is  only  1.77%,  but  a  saving  of  $1350  additional 
would  be  made  for  each  dollar  per  ton  increase  in  the  price  of  coal. 

Explosions  of  Economizers. — Explosions  of  economizers  are  rare, 
but  their  possibility  should  be  recognized  and  guarded  against.  They 
may  occur  from  overpressure,  due  to  closing  of  the  outlet  valve  or 
other  causes,  which  may  be  prevented  by  means  of  a  safety  valve. 
When  the  gas  inlet  damper  is  closed  there  is  a  possibility  that  it  may 
leak  combustible  gas  into  the  economizer  flue,  making  an  explosive 
mixture  which  might  be  ignited  by  a  lighted  torch.  The  headers 
or  tubes  may  be  weakened  by  internal  or  external  corrosion,  and  a  rup- 
ture might  occur  at  the  normal  working  pressure.  This  should  be 
guarded  against  by  annual  inspection  and  hydraulic  test  at  50  per 
cent  in  excess  of  the  working  pressure. 

The  "Unaccounted  for  Loss"  in  the  Heat-balance. — In  the  heat- 
balance  computed  from  the  results  of  a  boiler-test — see  Chapter  XIV, 
pages  575  and  581 — the  heat  which  is  "unaccounted  for"  sometimes 
amounts  to  quite  a  large  percentage  of  the  total  heating  value  of  the 
coal.  In  one  case,  with  soft  coal  very  high  in  moisture,  the  author 
found  it  to  be  more  than  20  per  cent,  even  after  a  liberal  allowance 
had  been  made  for  radiation.  Some  probable  causes  of  this  shortage 
in  the  heat-balance  are  the  following : 

1.  The  calculations  of  heat  lost  in  the  chimney-gas  are  based  on 
the  supposition  that  the  dry  gas  contains  only  C02,  CO,  0,  and  N". 
The  fact  is  that  for  a  short  period  after  each  firing  of  fresh  coal  the 
gas  may  also  contain  H,  formed  by  decomposing  the  moisture  in  the, 
coal,  and  CH4,  distilled  from  the  coal,  which  are  not  burned  because 
the  furnace  conditions  were  unfavorable.     The  gas  may  also  contain 
some  S02  and  N02,  from  the  sulphur  and  the  nitrogen  in  the  coal. 
As  much  as  1.37  per  cent  of  N02  has  been  found  in  chimney-gases 
by  Dr.  A.  H?  Gill.*    This  would  indicate  the  possibility  that  a  small 
quantity  of  oxides  of  nitrogen  may  be  produced  from  the  nitrogen 
of  the  air  in  the  boiler-furnace,  or  from  the  nitrogen  in  the  coal. 

2.  The  gas  analyzed  may  not  be  a  fair  average  sample  of  the  gas 
in  the  flue.     The  constitution  of  gas  produced  in  an  ordinary  furnace 
is  constantly  varying ;  within  a  space  of  ten  minutes  it  may  vary  from 
low  C02,  high  CO,  and  no  6,  through  high  C02,  no  CO,  and  low 
0,  to  low  C02,  no  CO,  and  high  0.     The  gas  is  also  apt  to  vary  in 
composition  in  different  parts  of  the  flue.    See  "Sampling  Flue-gases/' 
page  588. 

3.  The  analysis  for  C02,  CO,  0,  and  N   (by  difference)   may  be 
erroneous.     Sometimes  analyses  are  published  which  show  the  total 
of  CO 2,  CO,  and  0  to  be  only  about  16  per  cent.    It  is  very  improb- 

*  Engineering  News,  Feb.  18,  1897,  p.  107. 


MISCELLANEOUS.  697 

able  that  the  sum  of  these  gases  can  ever  be  as  low  as  16  per  cent  in 
boiler  practice,  except  possibly  for  a  minute  or  so  after  tiring  fresh 
coal,  when  large  volumes  of  H  and  of  CH4  may  be  given  off.  When 
carbon  is  thoroughly  burned  to  C02,  either  with  or  without  excess  of 
air  the  sum  of  C02  and  0  should  equal  20.9  per  cent,  and  the  N  79.1 
of  the  volume  of  the  gases.  Carbon  burned  to  CO  only,  without 
excess  of  air  would  give  a  gas  containing  34.5  per  cent  CO  and  65.5 
per  cent  N.  Hydrogen  burned  in  air  without  excess  would  give  a 
dry  gas  of  100  per  cent  N.  The  normal  value  of  the  sum  of  C02  and 
0  being  20.9  per  cent,  and  the  production  of  CO  by  imperfect  com- 
bustion tending  to  make  the  sum  of  C02,  CO,  and  0  higher  than  this 
figure,  it  would  require  the  burning  of  a  large  percentage  of  hydrogen, 
or  the  dilution  of  the  gas  by  a  large  volume  of  hydrocarbons,  to 
reduce  the  sum  of  C02,  CO,  and  0  to  as  low  a  figure  as  16.  If  the 
sum  is  below  19,  an  error  in  the  analysis  may  be  suspected. 

4.  With  some  kinds  of  coal,  especially  semi-bituminous,  which  is 
easily  broken  into  dust,  and  a  high  draft  pressure,  there  may  be 
a  considerable  loss  of  coal  by  its  being  blown  out  of  the  stack.  An 
example  of  a  loss  of  this  kind  is  seen  in  the  records  of  test  of  a 
locomotive  boiler  on  page  620. 

Loss  of  Fuel  Due  to  Keeping  Up  Steam-pressure  in  Idle  Boilers. — 
In  a  report  by  F.  R.  Low  to  the  Committee  on  Data  of  the  National 
Electric  Light  Association  (Electrical  World,  June  12,  1897)  some 
statistics  were  presented  showing  the  amount  of  coal  required  to  keep 
up  pressure  while  no  steam  or  water  is  being  taken  from  the  boiler. 
We  quote  from  the  report  as  follows: 

When  a  boiler  is  laid  off  it  becomes  a  drag,  the  coal  used  in 
maintaining  the  fire  in  a  condition  to  be  started  counting  for  nothing, 
so  far  as  steam-production  is  concerned.  The  engineer  of  a  Phila- 
delphia station  on  a  test  found  that  it  required  1200  Ibs.  of  buck- 
wheat coal  to  keep  up  a  pressure  of  125  Ibs.  on  two  water-tube  boilers, 
having  each  59  sq.  ft.  of  grate  surface.  This  was  0.424  Ibs.  per  sq.  ft. 
of  grate  surface  per  hour. 

A  five-days'  test  of  a  horizontal  tubular  boiler  showed  a  consump- 
tion of  0.35  Ib.  of  coal  per  sq.  ft.  of  grate.  Another  water-tube  boiler 
in  a  five-days'  test  used  0.5  Ib.  per  sq.  ft.  of  grate. 

A  Lancashire  boiler  with  mechanical  stokers  used  only  0.2  Ib.  of 
coal  per  sq.  ft.  of  grate  on  a  seven-days'  test. 

Two  other  water- tube  boilers,  one  on  a  seven-days'  test  and  the 
other  on  a  test  of  several  days'  duration,  used,  respectively,  0.7  and 
0.5  Ib.  of  coal  per  sq.  ft.  of  grate. 

In  each  of  these  cases  the  boiler  was  shut  off  from  the  main  and 
no  steam  or  water  taken  from  it.  The  coal  was  used  simply  to  main- 
tain the  pressure.  A  moderate  rate  of  combustion  is  12  Ibs.  per  sq.  ft. 
of  grate  per  hour.  Allowing  0.5  as  the  average  consumption  while 
standing,  the  coal  burned  by  a  boiler  in  this  way  would  be  4.17  per 
cent  of  that  burned  while  running  at  12  Ibs.  per  sq.  ft.  of  grate  for  the 
same  length  of  time. 


698 


STEAM-BOILER  ECONOMY. 


If  a  boiler  runs  sixteen  hours  a  day  at  an  average  rate  of  12  Ibs. 
of  coal  per  sq.  ft.  of  grate  per  hour,  and  stands  the  other  eight  with  a 
consumption  of  0.5  Ib.  per  sq.  ft.  of  grate  per  hour,  the  coal  used, 
while  idle,  will  be  2.04  per  cent  of  the  whole.  If  it  runs  half  the 
time,  the  expense  in  coal,  while  standing,  will  be  4.17  per  cent  of  the 
total  amount.  The  following  table  gives  the  percentages  for  different 
lengths  of  running  and  different  rates  of  combustion : 


Percentage  of  Total  Coal  Used  in  Idle  Boilers  at  .5  of  a  Pound  per 

Square  Foot  of^Grate  While  Idle. 

Hours 
Running. 

Hours 
Standing. 

Average  Rate  Combustion  per  Square  Foot  Grate  While  Running. 

12 

15 

18 

20 

24 

23 

1 

.18 

.15 

.12 

.11 

.10 

22 

2 

.38 

.30 

.25 

.23 

.19 

21 

3 

.59 

.47 

.40 

.36 

.28 

20 

4 

.83 

.66 

.55 

.50 

.41 

19 

5 

1.08 

.87 

.66 

.65 

.55 

18 

6 

1.37 

1.10 

.92 

.83 

.69 

17 

7 

1.69 

1.35 

1.13 

1.02 

.85 

16 

8 

2.04 

1.63 

1.37 

1.23 

1.03 

15 

9 

2.44 

1.92 

1.64 

1.48 

1.23 

14 

.      10 

2.89 

2.33 

1.99 

1.75 

1.44 

13 

11  - 

3.40 

2.73 

2.30 

2.07 

1.70 

12 

12 

4.00 

3.23 

2.70 

2.44 

2.04 

11 

13 

4.69 

3.79 

3.18 

2.87 

2.40 

10 

14 

5.51 

4.46 

3.75 

3.38 

2.83 

9 

15 

6.50 

5.26 

4.42 

4.00 

3.35 

8 

16 

7.69 

6.25 

5.26 

4.76 

3.85 

7 

17 

9.19 

7.41 

5.96 

5.79 

4.87 

6 

18 

11.11 

9.09 

7.69 

6.98 

5.88 

Coal  Used  in  Banked  Fires  not  a  Measure  of  Loss  by  Radiation. — 

The  heating  value  of  the  coal,  used  when  the  boiler  is  idle,  averaging, 
according  to  Mr.  Low's  report,  4.17  per  cent  of  that  used  when  it  is 
in  operation  and  burning  12  Ibs.  of  coal  per  sq.  ft.  per  hour,  is  not  to 
be  considered  a  correct  measure  of  the  heat  lost  by  radiation,  since 
when  the  fire  is  banked  or  the  draft  nearly  all  shut  off,  the  coal  con- 
sumed is  burned  with  an  insufficient  supply  of  air,  and  therefore 
develops  less  than  its  full  heating  value.  The  gases  evolved  from  the 
smouldering  fire,  whether  burned  or  unburned,  escape  into  the  chimney 
at  about  the  temperature  of  the  steam  in  the  boiler.  The  coal  burned 
while  the  boiler  is  idle  therefore  represents  the  sum  of  three  different 
heat  losses,  viz.,  that  due  to  imperfect  combustion,  the  heat  carried 
into  the  chimney,  and  the  heat  lost  by  radiation. 

Assuming  a  ratio  of  heating  to  grate  surface  of  40  to  1,  a  rate  of 
driving  of  3  Ibs.  of  water  per  square  foot  of  heating  surface  per  hour 
and  an  evaporation  of  8  Ibs.  of  water  per  pound  of  coal,  gives  a  rate 
of  combustion  of  15  Ibs.  of  coal  per  square  foot  of  grate  per  hour,  a 


MISCELLANEOUS. 


fair  figure  for  water-tube  boilers  with  anthracite  coal.  Taking  ihe 
consumption  per  hour  with  banked  fires  as  0.5  Ib.  per  square  foot  of 
grate,  gives  3^  per  cent  of  the  hourly  coal  consumption  when  running, 
a  figure  which  covers  all  the  losses  of  hea£  due  to  banking  fires.  The 
loss  due  to  radiation  should  be  considerably  less  than  this  figure. 

Cost  of  Coal  per  Boiler  Horse-power  per  Year, — Taking  a  com- 
mercial or  boiler  horse-power  as  an  evaporation  equivalent  to  34| 
Ibs.  of  water  from  and  at  212°  per  hour,  the  evaporation  per  pound 
of  coal  under  actual  conditions  of  feed-water  temperature  and  steam- 
pressure  at  from  5  to  10  Ibs.,  and  the  cost  of  coal  per  ton  of  2240  Ibs. 
at  from  $1  to  $5,  we  obtain  the  following  figures  for  cost  of  coal  per 
horse-power  per  year  of  360Q  hours  or  12  hours  per  day  for  300  days 
in  the  year,  and  per  year  of  8760  hours,  or  24  hours  per  day  for 
365  days. 

COST   OF   COAL  PER   BOILER  HORSE-POWER   PER   YEAR. 


Water 

Coal 

Evap. 
per  Ib. 
of 

per 
Boiler 
H.P. 

Year  of  3600  Hours. 
Cost  of  Coal  per  Ton. 

Year  of  8760  hours. 
Cost  of  Coal  per  Ton. 

Coal. 

per  hr. 

Jbs. 

Ibs. 

$1. 

$2. 

$3. 

$4. 

$5. 

$1. 

$2. 

$3. 

$4. 

$5. 

10 

3.45 

5.94 

11.09 

16.63 

22.18 

27.72 

13.49 

26.98 

40.48 

53.97 

67.46 

9 

3.83 

6.16 

12.32 

18.48 

24.64 

30.80 

14.99 

29.98 

44.97 

59.96 

74.96 

8 

4.31 

6.93 

13.86 

20.79 

27.72 

34.65 

16.86 

33.73 

50.59 

67.46 

84.32 

7 

4.93 

7.92 

15.84 

23.76 

31.68 

39.60 

19.27 

38.55 

57.82 

77.10 

96.37 

6 

5.75 

9.24 

18.48 

27.72 

36.96 

46.21 

22.49 

44.97 

67.46 

89.95 

112.43 

5 

6.90 

11.09 

22.18 

33.27 

44.36 

55.45 

26.98 

53.97 

80.95 

107.94 

134.92 

Boiler-room  Labor. — An  investigation  made  in  1896  for  the  Steam- 
users'  Association  of  Boston,  Mass.,  by  Mr.  E.  S.  Hale,  led  to  the 
following  conclusions  concerning  the  cost  of  boiler-room  labor: 

In  plants  containing  595  boilers  the  coal  consumption  was  8302 
tons  per  week,  or  700  tons  per  boiler  per  year  of  50  w-eeks.  The 
average  cost  of  boiler-room  labor  per  ton  of  coal  handled  was  48  cents, 
ranging  from  26  to  74  cents. 

The  cost  gradually  decreases  as  the  size  of  the  plant  increases, 
becoming,  however,  nearly  stationary  at  200  tons  per  week. 

The  men  fire  more  coal  (in  the  proportion  of  about  15  per  cent) 
and  receive  more  pay  (about  10  per  cent)  in  the  plants  that  run 
twenty-four  hours  a  day  instead  of  ten  hours  a  day,  the  result  being 
a  cost  per  ton  about  5  per  cent  less.  The  difference  is  not  quite  so 
marked  when  comparing  plants  burning  very  large  amounts  of  coal 
(200  tons  a  week). 


700  STEAM-BOILER  ECONOMY. 

The  labor  per  ton  of  coal  is  about  10  per  cent  less  for  a  steady 
load  than  for  a  variable  load  of  any  sort. 

.handling  coal  should  cost  about  1.6  cents  per  ton  per  yard  up  to 
five  yams,  Uien  about  0.1  cent  per  ton  for  each  additional  yard. 

Cheap  men  do  as  much  work  as  good  men,  so  that  the  cost  of 
labor  is  almost  always  less  per  ton  of  coal  with  cheap  men.  The 
quality  of  the  work  may  not  be  the  same,  so  that  the  cost  per  ton  of 
steam  is  not  necessarily  less. 

Wages  of  firemen  and  work  done  per  man  are  about  the  same 
from  Maine  to  Pennsylvania. 

One  man  (besides  night  man)  can  run  engine  and  fire  up  to  about 
10  tons  per  week. 

One  man  (besides  engineer  and  night  man)  can  fire  up  to  about 
35  tons  per  week. 

Two  men  (besides  engineer  and  night  man)  can  fire  up  to  about 
55  tons  per  week. 

Three  men  (besides  engineer  and  night  man)  can  fire  up  to  about 
80  tons  per  week. 

These  figures  assume  that  the  night  man  does  all  he  can  of  the 
banking,  cleaning,  and  starting. 

The  figures  are  for  average  conditions.  If  the  conditions  are 
exceptional,  as,  for  instance,  a  very  long  wheel  or  very  variable  load, 
proper  allowance  should  be  made. 

Mechanical  stokers  save  30  to  40  per  cent  of  labor  in  very  large 
plants  (over  200  tons  per  week),  20  to  30  per  cent  in  medium-sized 
plants  (50  to  150  tons  per  week),  and  save  no  labor  in  small  plants. 

Handling  Coal  and  Ashes  in  Large  Plants, — Mr.  Hale's  report 
gives  no  data  of  the  cost  of  handling  coal  in  large  modern  plants,  such 
as  electric-light  and  power-stations  In  the  best  modern  practice  the 
coal  received  by  car  or  boat  is  elevated  and  dumped  in  large  storage- 
bins  under  the  roof  of  the  boiler-house  by  means  of  suitable  hoisting 
and  conveying  machinery.  From  the  bins  it  is  led  down  by  means  of 
iron  pipes  and  fed  by  gravity  directly  into  the  hoppers  of  the  mechan- 
ical stokers.  The  ashes  are  dumped  from  the  ash-pits  of  the  several 
boilers  into  cars  or  storage-bins  in  a  tunnel  underneath.  By  such 
mechanical  methods  of  handling  both  coal  and  ashes  all  shoveling  is 
avoided,  and  the  cost  of  boiler-room  labor  per  ton  of  coal  may  thus  be 
made  much  less  than  the  lowest  figure  named  in  Mr.  Hale's  report. 
(See  table  of  labor  costs  in  the  Delray  station,  on  page  639.) 

Number  of  Boilers  to  Operate  in  a  Plant  with  Variable  Load. — 
In  an  electric  power  and  lighting  plant  where  the  maximum  load  dur- 
ing a  portion  of  the  day  may  be  five  or  more  times  the  load  between 
1  and  5  A.  M.,  the  question  arises  how  many  boilers  should  be  operated 


MISCELLANEOUS. 


701 


and  how  many  shut  down  with  banked  fires  at  the  different  periods 
of  the  day.  By  a  series  of  tests  of  one  boiler  it  may  be  found  what 
is  its  range  of  economical  load,  and  at  what  low  load  it  will  pay 
to  shut  it  down  and  transfer  its  load  to  other  boilers.  From  these 
results  a  computation  may  be  made  showing  at  what  total  load 
of  the  whole  plant  it  will  pay  to  shut  down  one  or  more  boilers.  At 
the  Armour  plant  at  the  Union  Stock  Yards,  Chicago,  there  are  32 
375  H.P.  boilers.  The  feed  water  is  continuously  recorded  by  a 
Venturi  meter.  A  chart  was  made  showing  the  number  of  pounds 
of  water  evaporated  per  hour  by  from  16  to  32  boilers,  each  running 
at  different  percentages  of  their  rated  load  up  to  160%. — (Power, 
March  25,  1913.)  From  this  chart  the  following  table  has  been  made. 
Having  such  a  chart  (or  table)  for  any  large  boiler  plant  and  knowing 
the  percentage  of  rating  below  which  a  boiler  is  not  economical,  an 
inspection  of  the  chart  shows  how  many  boilers  should  be  in  service 
for  a  given  total  load  so  that  the  average  rate  of  driving  should  be 
about  that  corresponding  to  the  most  economical  rate. 


PER  CENT  OF  RATED  LOAD  ON  BOILERS 

Number  of 
Boilers  in 

60 

80 

100 

110 

120 

130 

140 

150 

160 

Operation. 

THOUSANDS  OF  POUNDS  OF  WATER  EVAPORATED  PER  HOUR. 

16 

108 

144 

180 

198 

216 

234 

252 

270 

288 

18 

122 

162 

203 

223 

243 

263 

283 

304 

324 

20 

135 

180 

225 

248 

270 

292 

315 

337 

360 

22 

149 

198 

248 

272 

297 

322 

346 

371 

396 

24 

162 

216 

270 

297 

324 

351 

378 

405 

432 

26 

176 

234 

293 

322 

351 

380 

409 

439 

468 

28 

189 

252 

315 

347 

378 

409 

441 

472 

504 

30 

203 

270 

338 

371 

405 

439 

472 

506 

540 

32 

216 

288 

360 

396 

432 

468 

504 

540 

575 

Task  Setting  for  Firemen.* — That  the  high  thermal  efficiency  at- 
tained by  experts  during  boiler  tests  is  seldom  maintained  in  every- 
day practice  is  due  to  neglect  on  the  part  of  the  management  to: 

(a)  Record  the  conditions  causing  the  high  efficiency  during  the 
test. 

(b)  Instruct  the  men  how  to  regulate  these  conditions  in  order 
to  duplicate  the  test  results,  and 

(c)  Provide  an  incentive  to  the  men  for  striving  for  the  pur- 
pose desired  by  the  management  or  owners. 

Also  in  most  instances  there  is  no  assurance  or  proof  that  the 


From  a  paper  by  W.  N.  Polakov.     Jour.  A,  S.  M.  E.,  1913. 


702 


STEAM-BOILER  ECONOMY. 


high  test  efficiency  was  really  the  highest  attainable, 
guidance  the  fireman  needs  at  least  three  instruments : 
(a)   Indicating  steam  meter. 


For  practical 


(b)   Draft  gage. 

(«) " 


FIG.  286. — FIREMEN'S  INDICATOR. 


Indicator  for  the  coordination  of  the  condition  of  firing  with 
the  load  carried  by  the  boiler  at  any  moment. 

The  writer  arranges  on  the  dial  of  the  steam  flow  meter  an  inside 

dial,  as  shown  in  Fig.  286,  with 
numbers  indicating  the  required 
thickness  of  fuel  bed  correspond- 
ing to  the  number  of  pounds  of 
steam  drawn  from  the  boiler  and 
a  third  dial  with  numbers  in- 
dicating the  draft  which  is  neces- 
sary and  sufficient  to  supply  the 
required  quantity  of  air  for  the 
combustion  at  a  rate  called  for 
by  the  indicated  steam  demand. 
Thus,  if  the  pointer  shows  that 
steam  is  flowing  from  the  boiler 
at  the  rate  of  14,000  Ib.  per  hour, 
the  fireman  will  know  that  the 
thickness  of  coal  on  the  grates 
should  be  about  6J  ins.,  and  the 
draft  about  0.4  in.  of  water. 
The  next  information  vitally  important  for  the  fireman  is  the 
frequency  at  which  his  furnace  must  be  coaled  to  keep  the  fires  in 
best  condition.  The  method  adopted  by  the  Italian  Navy  is  most 
satisfactory,  consisting  chiefly  in  bell  signaling  at  intervals  in  pro- 
portion to  the  load  carried  by  the  boilers,  which  signaling  is  regulated 
by  clock  mechanism  connected  with  a  flow  meter.  For  use  in  a 
boiler  house  where  a  number  of  batteries  are  fired  independently  and 
it  was  desirable  to  eliminate  the  variations  of  load  among  them,  a 
modification  of  this  method  was  devised  to  equalize  the  driving  of 
each  furnace.  For  this  purpose  the  counter  of  the  feedwater  weigher, 
supplying  water  to  the  entire  boiler  house,  rings  the  bell  every  time 
a  certain  number  of  thousand  pounds  of  water  is  fed  to  the  boilers, 
thus  giving  notice  to  the  firemen  that  an  adequate  number  of  shovelsf ul 
must  be  thrown  into  each  furnace.  This  number  is  easily  determined 
since  the  weight  of  shovelful  of  coal  is  known  and  the  rate  of  apparent 
evaporation  at  the  given  condition  of  firing  is  a  constant. 

In  setting  a  task  for  firemen,  it  remains  to  be  determined  what 
the  scope  of  the  task  shall  be.  It  devolves  upon  the  management  to 
accumulate  the  detailed  and  exact  knowledge  of  the  most  favorable 
conditions  to  attain  results  and  make  it  possible  and  desirable  for 
every  employee  to  live  up  to  them.  It  is  for  the  employee,  on  the 
other  hand,  to  create  or  maintain  such  conditions  as  are  required  in 
the  instructions, 


MISCELLANEOUS.  703 

Various  schemes  used  as  the  basis  of  task  setting  for  firemen 
have  always  created  dissatisfaction.  Certain  of  these  are  as  follows : 

(a)  The  cost  of  steam  generated  was  used  for  the  basis  of  the 
task,  and  a  premium  offered  for  the  reduction  of  this  cost,  but  as 
firemen  have  no  control  over  the  purchase  of  fuel,  maintenance  of 
equipment,  etc.,  this  task  involved  the  standardizing  of  conditions  of 
combustion,  for  which  no  instruments  were  provided  and  no  definite 
standard  or  aim  was  set. 

(b)  The  high  percentage  of  C02  in  flue  gas  was  adopted  as  a 
task  basis  for  firemen  in  several  plants,  but  the  men  were  not  trained 
nor  were  they  even  shown  how  to  obtain  it. 

(c)  A  high  percentage  of  C02  and  low  percentage  of  combustible 
in  the  ashes,  were  factors  upon  which  another  attempt  was  made 
to  specify  the  firemen's  task. 

(d)  A  limit  on  coal  consumption  as  a  task  for  railroad  firemen 
was  favored  at  one  time.    This  idea  soon  demonstrated  its  weakness. 

The  common  cause  of  failure  of  such  schemes  has  been  the  desire 
to  make  a  short  cut  and  jump  over  preliminary  studies,  and  save  the 
time  and  trouble  of  training  men  in  a  systematic  and  thorough  man- 
ner how  to  accomplish  the  task  set  for  them. 

Neither  ratio  of  apparent  evaporation  nor  boiler  efficiency  nor 
efficiency  of  combustion  alone  are  anywhere  near  sufficient  for  the  pur- 
pose of  judging  the  efficiency  of  the  work  of  men. 

The  writer  has  devised  and  introduced  a  comparatively  simple 
method  of  obtaining  a  complete  record  of  firemen's  performance  and 
to  figure  their  efficiency.  This  method,  which  has  been  in  vogue  for 
over  a  year  at  the  central  station  at  Warrior  Eidge,  Pa.,  requires  the 
following  record  data : 

(a)  Coal  records  from  store  issue  tickets  and  coal  passers'  reports 
compiled  every  eight  hours. 

(b)  Heat  value  of  fuel  determined  by  bomb  calorimeter  and  value 
of  coal  in  B.T.U.  known  for  each  coal  pocket. 

(c)  Amount  of  water  fed  to  boiler  (banked  boilers  fed  separately) 
ascertained  for  the  same  periods. 

(d)  Temperature  of  feedwater  recorded. 

(e)  Steam  pressure  recorded. 

(/)   Degrees  of  superheat  recorded. 

These  data  are  turned  over  to  the  station  clerk  who  proceeds  as 
follows : 

(a)  From  a  slide  rule,  he  ascertains  the  factor  of  evaporation  on 
the  basis  of  absolute  boiler  pressure,  temperature  of  feed  and  tempera- 
ture of  superheat. 

(&)  By  means  of  a  Day  and  Zimmermann  power-plant  log  calcula- 
tor he  determines  for  each  watch,  or  for  each  man,  1,  the  actual 
evaporation  ratio ;  2,  factor  of  evaporation ;  3,  equivalent  evaporation ; 
4,  efficiency  of  steam  generation;  5,  cost  of  fuel  per  1000  Ibs.  of  steam. 
He  then  enters  the  results  of  computation  on  the  daily  power  plant 
report  form.  The  whole  procedure  takes  on  the  average  of  18  minutes 


704  STEAM-BOILER  ECONOMY. 

of  the  clerk's  time,  for  whom,  incidentally  a  specific  task  is  assigned 
and  sufficiently  hourly  bonus  offered  for,  its  fulfilment. 

Every  case  of  failure  on  the  part  of  any  fireman  to  secure  on  his 
watch  the  combined  boiler,  furnace  and  grate  efficiency  of  70  per 
cent  or  above  is  immediately  investigated  by  studies  of  other  records 
and  recording  charts  of  draft,  temperature  of  escaping  gases,  nature 
of  boiler  refuse,  etc.,  and  if  no  reason  can  be  found  there,  an  examina- 
tion of  the  physical  condition  of  equipment  and  apparatus  is  made. 
The  result  of  this  investigation  is  recorded  on  a  form  for  cause  of 
lost  bonus. 

Then  the  firemen  are  informed  as  to  the  results  of  their  work 
before  they  come  back  for  the  next  watch,  and  moreover,  while  they 
are  proceeding  with  their  work,  they  have  in  addition  to  instruments 
indicating  the  condition  of  firing,  continuous  information  as  to 
results  thev  are  accomplishing.  This  is  accomplished  by  having  coal 
weighing  and  water  metering  so  balanced  that  an  even  number  of 
dumps  of  feedwater  and  dumps  of  coal  indicates  that  the  ratio  of 
evaporation  (superheat,  pressure  and  feed  temperature  being  as 
specified),  is  on  the  safe  side  of  the  requirement. 

The  record  of  attainment  of  the  task  by  firemen,  kept  from  the 
start  of  task  work  in  the  boiler  house  at  Warrior  Ridge,  shows  steady 
improvement  and  better  habits  of  men.  While  the  May  record  showed 
only  68.7  per  cent  efficiency  of  boiler  and  grates  of  the  whole  plant, 
the  record  in  July  showed  the  efficiency  of  73.1  per  cent.  The  num- 
ber of  day-men  falling  short  on  the  task  is  steadily  reduced.  A  de- 
parture from  the  principle  of  separate  man's  record  proved  to  be  so 
gratifying,  creating  as  it  did  an  unusually  strong  team  spirit  of 
cooperation,  that  the  writer  has  never  attempted  to  split  the  records 
of  two  or  three  men  working  jointly  firing  one  battery  of  boilers. 

The  essential  thing  is  that  some  element  of  advantage  to  the  work- 
man be  introduced  sufficient  to  overcome  actual  or  imaginary  dis- 
advantages believed  by  the  men  to  exist  as  a  result  of  the  new  state 
of  affairs.  This  advantage  takes  the  form  of  a  sufficiently  attractive 
and  generous  bonus  to  be  paid  for  willingness  to  learn  the  new  way 
and  to  continue  to  observe  the  instructions. 

The  man  for  whom  a  certain  task  is  assigned  must  strive  to  accom- 
plish its  aim.  First.,  the  man  must  have  a  desire;  secondly,  he  must 
make  a  choice  of  ways  and  means;  and  thirdly,  he  must  perform 
necessary  actions. 

As  a  rule,  the  workmen  feel  that  the  adoption  of  a  new  method 
will  impose  an  undue  strain,  but  it  is  comparatively  easy  to  overcome 
this  misconception  with  the  firemen  from  the  fact  that  greater  effi- 
ciency means  less  coal  to  be  shoveled.  On  the  other  hand,  the  new 
conditions  require  the  men  to  give  their  attention  to  instructions  and 
the  indications  of  the  apparatus,  which  diverts  them  unpleasantly 
from  chatting  at  leisure  with  their  fellow  workmen.  This  forms  a 
a  more  serious  obstacle  to  their  quick  decision  in  favor  of  new  routine 
than  anything  else. 


MISCELLANEOUS.  705 

There  must  be  two  bonus  limits  established,  a  maximum  and 
a  minimum.  The  maximum  should  equal  the  net  saving  accom- 
plished under  given  circumstances,  the  minimum  is  zero.  When  the 
bonus  actually  paid  reaches  either  of  these  limits  it  loses  its  usefulness 
since  it  loses  its  stimulating  effect — with  the  management  if  the 
maximum,  and  with  the  men  if  the  minimum.  Since  in  an  average 
boiler  house  the  task  results  in  a  25  per  cent  saving  of  the  coal  bill 
while  the  firemen's  pay  roll  is  from  10  to  15  per  cent  of  the  coal  bill, 
there  is  a  considerable  latitude  for  adjustment  of  bonus. 

The  success  of  attainment  of  the  task  is  determined  by  detailed, 
patient  and  prolonged  training  and  instructions,  and  this  is  the 
most  important  function  of  the  management.  Additional  compen- 
sation and  exhaustive  training  are  imperative,  but  they  alone  are 
insufficient.  The  conditions  under  which  the  men  must  work  must 
be  so  arranged  as  to  insure  the  fullest  preservation  of  their  strength, 
health,  and  physical  faculties. 

In  a  boiler  house  the  amount  of  work  per  man  per  hour  is 
constant,  and  cannot  be  increased  without  knocking  down  the  effi- 
ciency to  a  ridiculously  low  figure,  but  the  number  of  foot-pounds  of 
work  can  be  reduced  in  an  inverse  proportion  to  the  increase  of 
efficiency,  so  that  the  question  of  preservation  of  a  man's  health  elimi- 
nates any  consideration  of  overspeeding.  The  conditions  which  tbpn 
remain  for  consideration  are  (a)  temperature  of  room;  (b)  ventilation 
(dust  and  draft)  ;  (c)  lighting;  (d)  drinking  water;  (e)  restful  seats; 
and  (/)  sanitary  washrooms. 

One  familiar  with  the  common  layout  of  a  power  plant  cannot 
over-emphasize  the  importance  of  the  above  conditions  to  enable 
the  men  to  live  up  to  their  task  day  in  and  day  out.  While  engine 
rooms  not  infrequently  offer  pleasant  and  sanitary  surroundings, 
boiler  houses  are  so  built  as  to  make  them  unbearably  cold  in  winter 
and  uncomfortably  hot  during  the  summer;  ventilation  apparently 
serves  either  to  fill  the  lungs  with  coal  dust  or  to  chill  the  perspiring 
men  after  cleaning  their  fires.  Lighting  is  an  unusual  luxury,  so  that 
after  looking  into  the  furnace  no  man  could  read  his  gages  or  examine 
anything  around  the  boiler.  Good  drinking  water  is  rarely  provided, 
and  restful  seats  with  backs  were  never  found  by  the  writer  in  any 
boiler  house. 

Steady  attention  on  the  part  of  the  fireman  is  much  more  important 
than  is  generally  realized.  Physical  condition  and  strength  being 
constant,  the  boiler  efficiency  percentage  is  in  an  almost  direct  pro- 
portion to  the  degree  of  attentiveness  of  the  fireman. 

In  our  experience  we  adopted  in  addition  to  time  studies,  a  careful 
investigation  of  fatigue,  both  mental  and  physical,  and  measurements 
of  the  vitality  of  the  men  affected  by  various  conditions  of  work  and 
number  of  working  hours  per  day.  Xo  task  is  reasonable  unless  the 
workman  can  fully  regain  his  loss  between  quitting  time  and  recom- 
mencing work  the  next  day,  and  during  a  sufficiently  long  period  of 
observation  a  man  should  be  able  to  gain  or  at  least  not  lose  anything 


706 


STEAM-BOILER  ECONOMY. 


in  his  vitality.  Observations  should  cover  at  least  four  factors: 
(a)  weight  of  body;  (b)  blood  pressure;  (c)  temperature  of  body; 
and  (d)  pulse.  Finally,  the  time  element  in  relation  to  task  setting 
for  men,  particularly  if  the  work  requires  a  considerable  strain,  must 
be  settled  by  examination  no  less  careful  than  the  study  of  the  time 
rate  of  driving  boilers.  When,  however,  as  in  the  case  of  firemen, 
both  physical  strain  and  attention  are  required,  it  was  found  that 
with  strong,  healthy  individuals  the  limiting  factor  on  number  of 
hours  of  profitable  work  is  set  not  by  physical  exhaustion  but  by 
weariness  of  spirit.  Other  conditions  being  equal,  a  fireman  on  a 
12-hour  watch  is  found  to  be  about  4-5  per  cent  less  efficient  than  the 
same  man  on  an  8-hour  shift. 

This  time-limiting  factor  on  human  efficiency,  taken  in  conjunction 
with  a  scientific  certainty  in  determination  of  the  most  advantageous 
thermal  efficiency,  formed  the  grounds  on  which  the  writer  rejected 
the  sliding  scale  of  bonus  rate  results  exceeding  the  task  set  by  various 
degrees.  The  task  set  must  be  so  little  below  the  most  advantageous 
point  that  it  could  be  reached  with  greatest  benefit  to  all  concerned, 
and  it  is  not  desirable  from  economical  aspects  either  to  fall  short 
of  or  considerably  to  overreach  it.  Offering  extra  compensation  for 


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55  60  65  70          75  80 

Boiler  and  Grate  Efficiency 


85 


FIG.  287.  —  RESULTS  OF  BONUS  PAYMENTS. 


excess  of  the  task  requirement  means  in  final  analysis  either  that 
the  investigator  did  not  determine  both  limits,  or  that  the  manage- 
ment tempts  a  man  to  do  more  than  the  average  employer  dares  to 
ask  directly. 

The    example    of    efficient    cooperation    between    employer    and 
employee  in  the   power   plants   of   public   utility   corporations   here 


MISCELLANEOUS.  707 

referred  to  demonstrated  the  value  of  the  a'bove  principles  for 
setting  task  and  accomplishing  the  predetermined  results  in  firing 
boilers. 

The  diagram  in  Fig.  287,  showing  cost  per  kilowatt-hour  of  fuel 
relative  to  firemen's  payroll  and  bonus  before  and  after  adoption  of 
scientific  basis  for  firing,  presents,  outside  of  the  interesting  reduc- 
tion in  cost  since  the  change  of  method  took  place,  another  feature 
also  of  no  less  importance,  namely,  that  since  that  time  the  unit  cost 
remained  practically  constant,  while  previously  it  fluctuated  con- 
siderably. 

A  Steam-boiler  Practice  of  the  Future, — Steam-boiler  practice  at 
the  present  day  is  in  a  rather  chaotic  state.  There  is  a  confusing  multi- 
plicity of  types  and  of  varieties  of  each  type.  With  any  given  style 
of  boiler  and  furnace  there  is  a  lack  of  uniformity  in  the  capacity  and 
economy  obtained  from  boilers  of  the  same  size  in  different  places. 
It  is  not  uncommon  to  find  two  or  three  different  styles  of  boilers  in 
the  same  boiler-house.  In  a  row  of  four  or  five  boilers  of  the  same 
size  and  style,  the  arrangement  of  the  flues  may  differ,  so  that  no  two 
of  them  have  the  same  draft,  and  consequently  no  two  of  them  develop 
the  same  power  or  give  the  same  economy. 

Besides  the  variety  in  types  and  in  the  conditions  of  running  of 
existing  boilers,  there  is  a  tendency  to  change  in  the  conditions.  The 
pressure  of  steam  required  by  engines  is  increasing.  The  small  sizes 
of  anthracite  are  being  used  instead  of  the  larger  sizes,  and  they 
require  stronger  draft,  and  larger  grate  surfaces,  and  give  more  trouble 
to  handle  ashes  and  clinker.  Soft  coal  is  in  many  places  displacing 
anthracite,  bringing  with  it  smoky  chimneys,  and  as  the  smoke  nuis- 
ance increases  new  devices  are  continually  being  brought  forth  to 
suppress  it.  Eeal  estate  in  cities  is  becoming  more  costly,  and  boilers 
are,  therefore,  designed  to  economize  space,  and  they  are  being  driven 
at  more  rapid  rates.  Bapid  driving  with  bad  water  means  more 
trouble  from  scale,  and  this  enlarges  the  business  of  makers  of  feed- 
water  purifiers,  scale-extracting  machinery,  and  "boiler  compounds." 
This  is  the  age  of  labor-saving,  and  in  order  to  reduce  the  labor  cost 
of  steam-making  automatic  stokers  and  mechanical  means  of  handling 
coal  and  ashes  are  introduced. 

The  changes  above  mentioned  are  now  in  progress,  but  the  day 
when  stationary  steam-boiler  practice  shall  reach  a  reasonable  degree 
of  uniformity,  such  as  has  been  reached  in  locomotives  and  in  marine 
engines  and  boilers,  seems  yet  far  distant.  The  fittest  will  survive  at 
last,  but  the  unfit  lives  a  long  time. 


708  STEAM-BOILER  ECONOMY. 

The  following  is  a  list  of  the  leading  types  and  varieties  of  boilers 
which  still  survive  in  stationary  practice  in  the  United  States : 

Internally  Fired. — Galloway,  Scotch  marine,  locomotive,  vertical 
tubular. 

Externally  Fired. — Shell  boilers :  cylinder,  two-flue,  horizontal,  and 
vertical  tubular;  water-tube  boilers:  inclined,  vertical,  and  curved 
tubes;  coil  or  pipe  boilers. 

Besides  these  there  are  numerous  combined  and  nondescript  types, 
and  modifications  of  standard  types,  which  usually  have  but  a  short 

life  in  the  market. 

* 

There  is  no  probability  that  any  increased  economy  of  fuel  may 
be  obtained  by  a  change  from  any  one  type  to  another,  if  the  condi- 
tions of  driving  remain  the  same.  With  any  one  of  these  types  an 
efficiency  of  from  70  to  nearly  80  per  cent  of  the  theoretically  possible 
may  be  obtained  from  good  anthracite  or  semi-bituminous  coal,  low  in 
ash  and  moisture,  and  burned  thoroughly  in  a  properly  designed 
furnace,  the  boiler  being  driven  at  its  most  economical  rate,  and 
proper  provision  being  taken  to  lessen  the  losses  from  radiation  and 
from  leaks  of  air  through  the  boiler-setting.  With  automatic  stokers 
and  with  proper  adjustment  of  the  air  supply,  high  efficiencies  may  be 
obtained  at  much  higher  rates  of  driving  than  are  commonly  used  with 
hand  firing. 

The  Survival  of  a  Type  will  Depend  on  Some  Oilier  Factor  than 
Economy  of  Fuel. — The  possible  economy  that  may  be  obtained  from 
all  types  being  equal,  the  standard  type  or  types  of  the  future  will  be 
selected  for  other  reasons  than  economy  of  fuel.  Chief  among  these 
reasons  are:  (1)  Safety  from  explosion.  (2)  First  cost.  (3)  Dura- 
bility. (4)  Facility  for  cleaning.  (5)  Cost  of  repairs  and  facility  for 
making  them.  (6)  Space  occupied.  (7)  Possibility  of  driving  at 
both  low  and  high  rates  of  evaporation  without  great  loss  of  fuel  econ- 
omy. (8)  Adaptability  of  the  boiler  and  furnace  to  different  kinds  of 
coal,  so  that  the  coal  may  be  changed  as  market  prices  vary. 

The  Boiler  Types  of  the  Future. — There  is  not  likely  to  be  any 
important  change  in  the  existing  types  of  boiler  used  in  stationary 
practice,  nor  is  any  new  type  likely  to  be  developed  which  will  offer 
any  advantages  over  the  present  types.  New  boilers  or  modifications 
of  old  ones  will  continue  to  be  invented,  and  some  of  them,  by  dint  of 
business  enterprise  and  liberal  advertising,  may  be  sold  in  considerable 
numbers,  but  the  farther  these  depart  in  their  construction  from  the 
existing  types  the  less  likely  are  they  to  be  permanently  successful. 


MISCELLANEOUS.  709 

The  survival  of  certain  types  in  the  struggle  between  those  now  on 
the  market  will  depend  not  on  economy  of  fuel,  as  has  already  been 
stated,  nor  on  cheapness  of  first  cost,  for  as  the  country  increases  in 
wealth,  boiler  users  become  more  willing  to  pay  fair  prices  for  the  best 
boilers.  It  will  depend  chiefly  on  the  factors  of  durability  and  facility 
for  cleaning  and  for  repairs.  Durability  depends  largely  on  the  kind 
of  water  used  in  a  boiler,  and  therefore  a  boiler  may  survive  in  New 
England,  where  the  water  is  generally  of  excellent  quality,  while  it 
may  be  condemned  in  many  sections  of  the  West,  where  the  water 
contains  large  amounts  of  scale-forming  material.  The  question  of 
economy  of  space  occupied  will  be  an  important  factor  in  determining 
the  type  of  boiler  to  be  used  in  large  plants  in  cities,  where  real  estate 
is  expensive. 

Boiler  Furnaces  of  the  Future. — The  greatest  improvement  which 
is  to  be  made  in  average  boiler  practice  is  the  adoption  of  furnaces  for 
burning  soft  coal  without  smoke.  In  ordinary  practice  in  the  Western 
States  an  efficiency  of  50  per  cent  or  less  is  not  uncommon,  with  the 
coal  burned  in  ordinary  furnaces.  It  is  quite  possible  to  raise  this  to 
70  or  even  80  per  cent  with  automatic  stokers,  furnaces  surrounded 
by  fire-brick,  provision  for  securing  the  intimate  admixture  of  very 
hot  air  with  the  distilled  gases,  and  controlling  the  air  supply  in  ac- 
cordance with  the  indications  of  gas  analyses.  The  raising  of  the 
efficiency  of  boilers  by  these  means  from  50  per  cent  to  75  per  cent 
would  effect  a  saving  of  many  millions  of  dollars  per  year,  and  it  would 
at  the  same  time  abolish  the  smoke  nuisance. 


INDEX 


Air   and    water    vapor,    weight    of, 
table,  20 

heated,  Ellis  &  Eaves  system,  240 

heated,  Howden  system,  239 

heated,  use  of  in  furnaces,  215 

leaks  in  boiler  settings,  645 

properties  of,  19 

supply,  calculated  from  gas  analy- 
sis. 33 

supply,  excess,  34 

supply  for  different  grades  of  coal,  36 
Air-supply,  regulating  apparatus,  478 
Alabama  coal-fields,  117 
Alarm,  high-  and  low-water,  479 
Alaska  coals,  136 
Allen  water-tube  boiler,  354 
Almy  water-tube  boiler,  358 
Alternate  firing,  212 
Analyses  of  coal,  different  methods  of 
reporting,  73 

of  coals,  48,  563 
Analysis  of  flue  gas,  491 

of  gases,  apparatus  for,  578 

of  gases,  errors  in,  38 
Anderson  boiler,  627 
Andrews  boiler,  626 
Anthracite,  burning  of,  197 

coal,  99 

range  of  results  of  tests  with,  623 

sizes  of,  99 

Argand  steam-blower,  206 
Arizona  lignite,  138 
Arkansas  coal  beds,  127 
Ash,  analyses  of,  54 

composition  and  fusibility,  53 
Ash-handling  in  large  plants,  700 
Attachments  to  boilers,  467 

Babcock  &  Wilcox  chain-grate  stoker, 
222 

water-tube  boiler,  360,  373,  652 
Baffling  of  gases,  of  water-tube  boilers, 

594 
Bagasse  fuel  in  sugar  manufacture,  178 

drying  with  waste  heat,  180 
Banked  fires,  loss  of  fuel  in,  697 
Belleville  water-tube  boiler,  357 
Bituminous  coal,  51 

coal  fields  of  the  U.  Sv  103 


Blechynden's    experiments    on    heat 

transmission,  325 
Blower,  Argand  steam,  206 
Blowers,  fan-  and  steam-,  200 
Blow-off  pipe,  462 

tank,  462 

valve,  462,  476 

surface,  477 

Boiler    capacity    and    efficiency,    see 
Capacity,  Economy,  Efficiency 

compounds,  523,  526 

efficiency  (see  Efficiency),  12 

evolution  of  forms  of,  341 

forms  in  different  countries,  374 

horse-power  (see  Horse-power),  11 

life  of  a,  547 

operation,  12 

performance,  386 

plant  design,  397 

plant  in  France,  401 

plant  in  Chicago,  402 

practice  of  the  future,  707 

setting,  452 

setting,  bad,  504 

shell,  making  a,  426 

troubles  and  complaints,  500 

dimensions  of  standard  forms,  438 

forms  of,  341,  625 
Boilers,  shell  or  fire-tube: 

Andrews,  626 

Cornish,  342 

cylinder,  269 

elephant,  342 

Exeter,  627 

Galloway,  343 

Lancashire,  343 

locomotive,  347 

Lowe,  624 

Manning,  347 

multitubular,  344 

vertical  tubular,  346 
Boilers,  water-tube,  351 

early  forms,  352 

recent  forms,  353 

modern  forms,  360 

Allen,  354 

Almy,  358 

Anderson,  627 

Babcock  &  Wilcox,  360,  373 

711 


712 


INDEX. 


Boilers,  Belleville,  357 

Dance,  357 

Field,  353 

Firmenich,  259 

Fitch  &  Voight,  352 

Fletcher,  353 

Gill,  362 

Gurney,  355 

Harrison,  626 

Hazelton,  355 

Heine,  219,  365 

Herreshoff,  358 

Hohenstein,  649 

Joly,  353 

Kelly,  355 

Kilgore,  357 

Maynard,  360 

Miller,  354 

Parker,  369 

Phleger,  357 

Pierce,  627 

Roberts,  358 

Rogers  &  Black,  357 

Root,  362 

Rowan,  357 

Rust,  367 

Smith,  626 

Stevens,  352 

Sterling,  366 

Thornycroft,  371 

Ward,  357 

Wheeler,  360 

Wickes,  366 

Wiegand,  354 

Wilcox,  356 

Yarrow,  654 
Braces  and  stays,  429  ^ 
Brackets  and  hangers,  466 
Breechings  and  smoke  flues,  design  of, 

684 

Briquettes,  167 
Briquetted  coal,  tests  of,  169 
Brown  coal,  see  Lignite 
Buckwheat  coal,  see  Anthracite 
Burning  Illinois  coal  without  smoke, 
232 

soft  coal,  wrong  method,  207 

Caking  and  non-caking  coals,  50 
Calculation  of  weight  of  gases  from 

their  analysis,  33 
Calculations  of  results  of  a  boiler  test, 

569,  591 
California  coal,  139 

fuel  oil,  185 

Calking  of  riveted  joints,  428 
Calorific  value,  see  heating  value 
Calorimeter,  Mahler's  coal,  144 

Parr's  coal,  152 

steam,  normal  reading  of,  584 


Calorimeters,  steam,  583 

Cannel  coal,  51 

Capacity  depends  on  economy,  269 

of  a  boiler,  definition,  11 

of  a  plain  cylinder  boiler,  281 
Carbon,  combustion  of,  8 

monoxide  formed  from  CC>2,  13 

produced  by  heavy  firing,  33 

nature  of,  17 
Centennial  Exhibition  boiler  tests,  277, 

624 

Chain-grate  stokers,  221 
Chart  of  a  boiler  trial,  592 
Chemistry  of  fuel  and  combustion,  17 
Chimney  draft  theory,  671 
Chimney  gases,  see  Gases  * 

gases,  loss  of  heat  in,  table,  37 

table,  679,  682 

temperatures   at   different   heights, 

676 
Chimneys,  radial  brick,  686 

reinforced  concrete,  687 

size  of,  for  given  boilers,  677 

smoky,  not  necessary,  208 

with  forced  draft,  680 
Church  water-tube  boiler,  356 
Circulation,  effect  on  economy,  330 

water,  396 

Classification  of  coal,  46,  58,  73 
Clinkering  in  furnaces,  553 
Co2  recorders,  492,  496 

relation  to  O  in  boiler  tests,  644 
Coal    analyses    and    heating    value, 
diagrams  and  tables,  60-72 

analyses  of,  48 

caking  and  non-caking,  50 

cannel,  51 

classification  of,  46,  58,  73 

cost  of  per  boiler  horse-power,  699 

deterioration  of,  in  storage,  165 
Coal-dust,  170 

furnaces  for,  245 

Coal-fields  of  the  United  States,  98 
(see  names  of  the  States  in  this 
index) 
Coal,  formation  of,  44 

heating  value  of,  54 

hygro.metric  properties  of,  40 

long-  and  short-flaming,  50 

methods  of  sampling,  94 

production  in  U.  S.,  42 

relation    of    quality    of,    to    boiler 
capacity  and  economy,  80 

sampling  and  drying,  562 

selection  of,  83 

sizes  of  anthracite,  99 

sizes  of  bituminous,  577 

specifications  for  purchase  of,  85 

spontaneous  combustion  of,  95 

tests  of  heating  value,  141 


INDEX. 


713 


Coal,  valuing  by  tests  and  by  analysis, 

83 

Code  of  rules  for  boiler  tests,  559 
Coefficient  of  performance,  318 
Coke,  analyses  of,  167 
Coke-oven  and  blast-furnace  gas,  tests 

with,  648 

Coking  system  of  firing,  211 
Colorado  coals,  102,  131 
Combustion,  chemistry  of,  17 

complete,  methods  of  securing,  209, 
211 

heat  of,  7 

of  fuel,  8 

rate  of,  due  to  height  of  chimney, 
674 

spontaneous,  95 

Complaints  concerning  boilers,  500 
Corn  as  fuel,  193 
Cornish  boiler,  342 
Corrosion,  causes  of,  513 

external,  546 
Criterion  of  boiler  performance,  295, 

622 

Culm,  anthracite,  tests  with,  599 
Cumberland,  Md.  coal  field,  110 
Cylinder  boiler,  capacity  of  a,  269 

disadvantages  of,  282 

saving  of  waste  heat  from,  283 

Damper  regulation,  236 

regulators,  474 
Dance  water-tube  boiler,  357 
Decomposition,  heat  absorbed  by,  22 
Definitions,  1 
Designing  boilers  for  a  street  railway, 

403 

Design  of  boilers  and  boiler  plants,  397 
Dimensions  of  boilers,  439 
Down-draft  furnaces,  218 
Draft   and    flue-temperature,  relation 
to  rate  of  driving,  238 

apparatus  for  forced,  237 

due  to  height  of  chimney,  673 

forced  and  induced,  234,  239 

forced,  calculations  for,  240 

gauge,  585 
Draft-gauge,  Blonck,  488 

EUison,  488 

Uehling,  490 

loss  through  a  water-tube  boiler,  236 

poor  501 

regulation  of,  for  oil  firing,  683 

relation  of,  to  boiler  capacity,  238 
Drying  of  coal,  562 
Dryness  of  steam,  395 
Dry-pipe,  463 
Dulong's  formula,  8,  23 

reliability  of,  76 
Durability  of  boilers,  392 


Durston's  experiments  on  transmission 

of  heat,  329 
Dust-fuel,  see  Coal-dust 

Economizers,  689 

explosions  of,  696 
Economizer,  when  to  install,  695 
Economy,  effect  of  circulation  on,  330 

maximum,  means  for  securing,  508 

maximum  possible,  277 

of  fuel,  elementary  principles,  272 

range  of  in  practice,  596 

relation  to  quality  of  coal,  80 

relation  to  rate  of  driving,  277 
Ellis  &  Eaves  hot-air  system,  240 
Efficiency  (see  also  Economy),  12,|379, 
570 

definition  of,  570 

depends  on  six  factors,  304 

does  not  depend  on  type  of  boiler, 
332 

effect  of  incomplete  combustion  on, 
315 

effect  of  variable  conditions  on,  296 

effect  of  velocity  of  gases  on,  334 

formulas,  234,  315,  323 

maximum  possible,  306 

of  a  furnace,  579 

of  riveted  joints,  421 

of  the  heating  surface,  14,  285 

relation  of,  to  quality  of  coal,  322 

relation  to  rate  of  driving,  325,  616 

"true,  "336 

with  varying  air  supply,  314,  320 
Elephant  boiler,  342 
Equivalent  evaporation,  definition,  11 
European  coals,  Mahler's  tests  of,  141 
Evaporation,  factors  of,  table,  666 

tests,  see  Tests 

Evolution  of  forms  of  boilers,  341 
Exeter  boiler,  627 
Explosion,  danger  of,  391 
Explosions  caused  by  hidden  defects, 
547 

causes  of,  550 

of  economizers,  696 

Factors  of  evaporation,  table,  667 
Feeding  boilers,  467 
Feed-water,  see  also  Water 

bad,  512 

filter,  483 

indicators,  481 

regulators,  474 
Field  water-tube  boiler,  353 
Fire-brick  for  furnaces,  460 
Fire-doors,  464 
Fire-engine  boilers,  rapid  driving  of, 

641 
Firemen,  task  setting  for,  701 


714 


INDEX. 


Fire-room  operating  methods,  638 
Fire,  temperature  of,  26,  30 
Firing,  alternate,  212 

coking  system  of,  211 

improper,  507,  509 
Firmenich  water-tube  boiler,  359 
Fitch  &   Voight's   water-tube   boiler, 

352 

Fittings,  pipe,  464 
Flame,  nature  of,  9 
Flaming,  long-  and  short-,  coals,  56 
Flat  stayed  surfaces,  432 
Fletcher  water-tube  boiler,  353 
Flue-gas,  see  Gas 

analysis,  491 

Flues  and  gas  passages,  proportions  of, 
385 

subjected  to  external  pressure,  436 
Foaming,  causes  of,  512 
Forced  draft,  234 

draft  apparatus,  237 
Formula,   straight-line,  for  efficiency, 

ooo 

Formulas  for  efficiency,  234,  315,  323 
Fuel,  chemistry  of,  17 

combustion  of,  8 
Fuels  other  than  coal,  167 
Furnace  arches,  fire-brick,  458 

efficiency,  579 

for  burning  buckwheat  coal,  203 

location  of,  195 

not  adapted  to  coal,  503 

requirements  of  a  good,  197 

the  "wing-wall,"  213 

volume  required  for  complete  com- 
bustion, 267 
Furnaces,  downward  draft,  218 

for  burning  coal-dust,  245 

for  sawdust,  tan  bark,  etc.,  266 
Future  boiler  practice,  707 

Galloway  boiler,  343 
Gas  analyses,  errors  in,  38 

analysis,  491 

analysis  apparatus,  578 

analyses  in  tests  of  a  water-tube 
boiler,  610 

analyses,  variation  in,  641 

coke-oven   and  blast-furnace,   tests 
with,  648 

fuel,  191 

natural,  boiler  tests  with,  657 
Gas-works  residuals  as  fuel,  190 
Gases,  sampling  of,  494 

table  of  densities  of,  21 

temperature  of,  see  Temperature 
Gauges,  steam,  480 
Georgia  coal-field,  117 
Gill  water-tube  boiler,  362 
Graphite  as  a  scale  preventive,  534 


Grate  and  heating  surface  required  for 

a  given  power,  379,  383,  409 
Grate-bars,  201 

Grates,  shaking  and  dumping,  203 
Grate  surface  insufficient,  503 
Graphic  record  of  a  boiler  test,  592 
Grooving  of  boiler  shells,  518 
Guarantees  by  bidders,  412 
Gurney  water-tube  boiler,  355 

Hardness  of  water,  537 
Harrison  boiler,  626 
Hawley  down-draft  furnace,  219 
Hazelton  water-tube  boiler,  355      4 
Heads  of  boilers,  422 
Heat  absorbed  by  decomposition,  22 
Heat  balance,  571,  580 
Heat  balance,  unaccounted  for  loss  in, 
696 

latent,  4 

nature  and  measurement  of,  2 

of  combustion,  7 

quantity  of,  in  a  body,  6 

specific,  4 

transfer  of,  10 

Unit,  definition,  3 

Heat  transmission,  Blechynden's  tests, 
325 

Durston's  tests,  329 

in  economizers,  694 

not    proportional    to    temperature 
difference,  337 

through  plates,  287 
Heated  air,  use  of,  in  furnaces,  215 
Heating-surface,  effect  of    increasing, 
310 

efficiency  of,  14,  285 

insufficient,  276,  511 

measurement  of,  381 

of  water-tube  boilers,  442 

required  for  given  power,  379 
Heating-value,  available,  of  hydrogen, 
23 

of  a  fuel  containing  hydrogen  and 
water,  26 

of  coal,  54 

of  coal,  errors  in  reported,  57 

of  coals,  tests  of,  141 

of  fuel  oil,  185 

of  mixed  fuels,  23 

Heating  values  of  substances,  table,  21 
Heine  water-tube  boiler,  219,  365 
Hempel  apparatus  for  analyzing  gas, 

579 

Herreshoff  water-tube  boiler,  358 
Hohenstein  boiler,  649 
Hollow  walls'not  an  advantage,  459 
Horse-power,  builders'  rating,  382 

of  a  boiler,  11,  376 
Howden  hot-air  system,  239 


INDEX. 


715 


Humidity,  table,  19 
Hydrogen,  available  heating  value  of, 
23 

combustion  of,  8 

in  coal,  effect  of,  on  efficiency,  300 

nature  of,  17 
Hygrometric  properties  of  coal,  40 

Idaho  lignite,  139 
Illinois  coal,  122 

coal  field,  120 

coals,  burning  without  smoke,  233 
Incrustation  or  Scale,  518 
Indiana  coal,  120 
Induced  draft,  234,  239 
Iowa  coal,  125 

Johnson's  tests  of  American  Coals,  141 
Joly's  water-tube  boiler,  353 
Jones  underfeed  stoker,  227 

Kansas  coal,  126 
Kelly  water-tube  boiler,  355 
Kentucky  coal-fields;  114,  121 
Kerosene,  for  removing  scale,  533 
Kilgore  water-tube  boiler,  357 

Labor  cost  of  operating  boilers,  639 

in  boiler  room,  699 

Lancashire   and   multitubular   boilers 
compared,  333 

boiler,  343 

Lap  joint  dangerous,  548 
Latent  heat,  4 
Leakage  of  air  in  boiler  settings,  506, 

645 

Lightning  conductors,  684 
Lignite,  decrease  of  weight  of,  52 

definition,  51 

tests  of,  647 

Lignites  and  lignitic  coals,  137 
Liquid  fuel,  see  Oil 
Load-diagram  of  a  steam-plant,  405 
Locomotive  boiler,  347 

tests  of  a,  618 

Locomotives,  mechanical  stokers  for, 
232 

superheated  steam  in,  655 

tests  of  briquetted  coal  in,  169 
Lord  &  Haas's  tests  of  American  coals, 

153 
Lowe  boiler,  624 

Mahler's  coal  calorimeter,  144 
tests  of  European  coals,  141 

Manholes  and  handholes,  437 

Manning  boiler,  347 

Maps  of  coal-fields  of  U.  S.,  98 

Marine  boiler,  Scotch,  349 
water-tube  boilers,  370 


Maryland  semi-bituminous  coal,  110 
Massachusetts,  graphitic  coal  in,  98 
Materials  used  in  boilers,  412 
Maynard  water-tube  boiler,  360 
McClave  shaking  grate,  205 
Megass,  see  Bagasse 
Meter,  steam,  484 

V-notch  water,  481 

Venturi,  480 

Meters,  water,  calibration  of,  577 
Michigan  coal-field,  1 19 
Miller  water-tube  boiler,  354 
Missouri  coal-basin,  124 

C9al,  125 

Moisture  in  air,  effect  of,  on  efficiency, 
300 

in  coal,  determining,  582 

in  coal,  effect  on  boiler  efficiency,  315 

in  steam,  determining,  583 
Montana  coals,  133 
Mud-drums,  461 
Multitubular  boiler,  344 
Murphy  automatic  furnace,  226 

Nevada  coal,  139 
New  Mexico  coals,  103,  132 
New  River,  W.  Va.  coal,  113 
Nitrogen,  nature  of,  18 
North  Carolina  coal,  112 
North  Dakota  lignite,  139 
Nozzles  for  attaching  pipes  to  boilers, 
466 

Ohio  coal-field,  118 
Oil  burners,  250 

fuel,  181 

fuel,  boiler  tests  with,  648 

fuel,  specifications  for,  187,  189 

fuel,  tests  of,  187 
Oil  versus  coal  as  fuel,  188 

viscosity  of,  190 
Oklahoma  coal-fields,  128 
Operation  of  a  boiler,  12 

of  large  boiler  plants,  638,  700 
Oregon  coal,  139 

Orsat  apparatus  for  analyzing  gas,  578 
Oxygen  and  air  required  for  combus- 
tion, table,  20 

in    the    gases,    best    indication    of 
furnace  conditions  507 

nature  of,  18 

recorder,  497 

Painting  to  prevent  pitting,  517 
Parker  water-tube  boiler,  369 
Parr's  calorimeter,  152 
Peak-loads,  economy  at  high  rates  of 

driving,  237 
Peat  or  turf,  172 
Pennsylvania  coal  beds,  99,  104,  107 


716 


INDEX. 


Permutit  water-softening  process,  544 

Petroleum  as  fuel  (see  Oil),  181 

F  hleger  water-tube  boiler,  357 

Pierce  boiler,  627 

Pipe  connections  to  boilers,  463 

Pitot-tube  meters,  water  and  steam, 
481,  484 

Pitting  of  boiler  shells,  513,  517 

Plants,  modern  boiler,  399 

Plates,  thickness  of,  423 

Pocahontas  coal,  111 

Points  of  a  good  boiler,  388 

Powdered  coal,  170 

Prat  induced  draft  system,  239 

Pressed  fuel,  or  briquettes,  167 

Pressures  allowed  on  boilers,  417,  424 

Principles,  elementary  of  boiler  econ- 
omy, 269 

Producer-gas,  192 

Purchase  of  coal  on  specifications,  85 

Purification  of  water,  524 

Pyrometer,  Uehling,  494 

Quality  of  steam,  corrections  for,  569 
Quantity  of  heat  in  a  body,  6 

Radiation,  loss  of  heat  by,  279,  290,  698 
Eailroads,  coal  consumption  on,  621 
Railway  plant,  designing  boilers  for, 

Rating  of  boilers,  382 
Reinforcing  of  manholes,  438 
Repairs  of  boilers,  393 
Report,  form  of,  for  a  boiler  test,  572 
Residuum  oil,  183 
Retarders,  240 
^Return-tubular  boiler,  344 
Rhode  Island  graphitic  coal,  98 
Riley  underfeed  stoker,  230,  640 
Ringelmann  smoke  chart,  589 
Riveted  joints,  forms  of,  418 

proportions  of,  419 
Roberts  smoke  chart,  488 

water-tube  boiler,  358 
Rogers  &  Black  water- tube  boiler,  357 
Roney  stoker,  225,  612 
Root  water-tube  boiler,  362 
Rowan  water-tube  boiler,  357 
Rust  water-tube  boiler,  367 

Safety-valves,  469 

Sampling  and  drying  coal,  562 

methods  of,  94 
Sampling  of  flue  gases,  494,  563,  588 

steam,  563 
Sawdust  as  fuel,  175 

furnaces,  266 
Scale,  danger  from,  521 

effect  of,  on  efficiency,  520 

facility  for  removal  of,  393 


Scale,  methods  of  prevention  and  re- 
moval, 522 

or  Incrustation,  518 
Scotch  Marine  boiler,  349 
Selecting  a  new  type  of  boiler,  388 
Semi-anthracite,  Sullivan  Co.,  Pa.,  100 
Separators,  steam,  478 
Setting  of  a  horizontal  boiler,  452 

of  boiler,  bad,  504 

Shells,  water-  and  steam-drums,  417 
Smith  boiler,  626 

Smoke  abatement,  progress  in,  210 
Smoke  chart,  Ringelmann,  589 

Roberts,  488 

Smoke  determinations,  methods  of,  561 
Smoke-flues  and  breechings,  design  of 

684 
Smoke,  how  to  avoid,  209 

may  be  burned,  9 
Smoke-prevention,  success  of,  209 
Smokeless  furnace  for  Illinois  coal,  233 
Specifications  for  fuel  oils,  187,  189 

for  horizontal  tubular  boilers,  442 

for  purchase  of  coal,  85 
Specific  heat,  4,  340 
Spontaneous  combustion  of  coal,  95 
Starting  and  stopping  a  boiler  test,  567, 

590 

Staybolts,  431 

Stayed  surfaces,  rules  for,  432 
Steam-boiler,  see  Boiler 
Steam-dome,  obsolete,  462 
Steam,  dry,  identification  of,  661 
Steam  gauges,  480 
Steam-jets  in  furnaces,  215 

tests  of,  216 
Steam  meters,  484 

properties  of,  660,  662 

separators,  478 
Steel,  quality  of,  413 

quality  of  after  30  years'  service,  416 
Stevens  water-tube  boiler,  352 
Stirling  water-tube  boiler,  366,  612 
Straw  as  fuel,  177 
Strength  of  riveted  seams,  418 
Stokers,  advisability  of  using,  220 

mechanical,  types  of,  221 

results  of  tests  with,  632 
Storage,  deterioration  of  coal  in,  165 
Sub-bituminous  coal  and  lignite,  51 
Sulphur  in  coal,  heating  value  of,  39 

in  fuel,  18 
Superheater,  Foster,  499 

of  Heine  boiler,  365 
Superheated  steam  in  locomotive  ser- 
vice, 655 

steam,  properties  of,  666 
Superheating  of  steam,  498 

surface,  proportions  of,  382    . 
Surface  blow-off,  476 


INDEX. 


717 


Tan-bark  as  fuel,  176 
furnaces,  266 

Tar  as  fuel,  190 

Taylor  underfeed  stoker,  228,  612,  632 

Temperature,    maximum,    of   burning 

carbon,  27 

maximum  of  burning  hydrogen,  28 
measurement  of,  2 
of  fire,  26,  30 
of  gases  depends  on  rate  of  driving, 

274 

in  furnace  and  in  flue,  307 
of   furnace   and   extent   of   heating 
surface,  308 

Tennessee  coal-field,  116 

Tests,  boiler,  A.  S.  M.  E.  code,  559 
by  Mr.  Barrus,  597 
erroneous  conclusions  from,  594 
evaporation,  objects  of,  557 
evaporative,  results  of,  596 
impossible  results  of,  629 
of  a  B.  &  W.  marine  boiler  with  oil 

fuel,  652 
of  a  Corliss  vertical  tubular  boiler, 

630 

of  a  locomotive,  618 
of  an  Edge  Moor  boiler,  635 
of  a  Rust  water-tube  boiler,  630 
of  a  Thornycroft  boiler,  608 
of  a  Yarrow  boiler  with  oil  fuel,  649 
of  boilers  with  Taylor  stokers,  632 
of  heating  value  of  coal,  141 
of  American  coals,  Lord  &  Haas,  153 
of  marine  water-tube  boilers,  605, 

611 

of  Riley  stokers,  640 
of  Stirling  boilers  of  2365  H.  P.,  612 
of  Stirling  boilers  with  anthracite, 

598 

of  two-flue  boilers,  603 
of  washed  coal,  645 
rules  for,  559 
with  anthracite,  range  of  results  in, 

623 

with  lignite,  647 
with  oil  fuel,  648 

Texas  coal-beds,  129,  137 

Thermal  Unit,  3 

Thornycroft  water-tube  boiler,  371,  608 

Tile-roof  of  furnace,  223,  654 

Transfer  of  heat,  10 

Transmission  of  heat  through  plates, 
287,  325 


Troubles  with  boilers,  500 
Tubes,  dimensions  of,  435 

expanded,  holding  power  of,  428 

quality  of,  415 

Tube-spacing  in  horizontal  boiler,  436 
Turf  or  peat,  172 
Two-flue  boiler,  342 

Underfeed  stokers,  227 
Unit,  British  thermal,  3 

of  evaporation,  4 

United  States,  coal  production  in,  42 
Utah  coals,  134 

Valuing    of    coals    by    test    and    by 

analysis,  83 
Venturi  meter,  480 
Vertical  tubular  boiler,  346 
Virginia  coals,  102,  111 
Volatile  matter,  nature  of  the,  79 

Ward  water-tube  boiler,  357 
Washed  coal,  tests  of,  645 
Washington  coals,  134 
Water-  and  steam-space,  394 
Water-grate  of  down-draft  furnace,  219 
Water  meters,  calibrating,  577 

method  of  testing,  536 

methods  for  purification  of,  538 

-softening  apparatus,  535 

space  in  a  boiler,  395 

weight  of,  at  different  temperatures, 

658 

Water-tube  boilers  (see  Boilers,  water- 
tube),  351 

cleaner,  478 
Weathered  coals,  161 
Weathering  of  coal,  165 
West  Virginia  coal-fields,  112 
Wet  steam,  foaming,  512 

tan-bark  as  fuel,  176 
Wheeler  water-tube  boiler,  360 
Wickes  water-tube  boiler,  366 
Wiegand  water-tube  boiler,  354 
Wilcox  water-tube  boiler,  356 
Wing-wall  furnace,  213 
Wood,  analysis  of,  174 

heating  value  of,  174 
Wyoming  coals,  132,  160 

Yarrow  boiler,  649,  654 

Zinc  plates,  remedy  for  corrosion,  515 


GENERAL  LIBRARY 
UNIVERSITY  OF  CALIFORNIA— BERKELEY 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

This  book  is  due  on  the  last  date  stamped  below,  or  on  the 

date  to  which  renewed.  «• 

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31 


"• 


JUL. 


1 1  ia55  (ji 


JUN  15 


JUN  7    1956  L  U 


. 
LIBRARY  USE 

JUN  1  5 1960 


LD  21-100m-l,'54(1887sl6)476 


